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How to avoid blocking of scrolling itself when using setNestedScrollingEnabled(false)?

Background
We have quite a complex layout that has CollapsingToolbarLayout in it, together with a RecyclerView at the bottom.
In certain cases, we temporarily disable the expanding/collapsing of the CollapsingToolbarLayout, by calling setNestedScrollingEnabled(boolean) on the RecyclerView.
The problem
This usually works fine.
However, on some (bit rare) cases, slow scrolling on the RecyclerView gets semi-blocked, meaning it tries to scroll back when scrolling down. It's as if it has 2 scrolling that fight each other (scroll up and scroll down):
The code to trigger this is as such:
res/layout/activity_scrolling.xml
<android.support.design.widget.CoordinatorLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context="com.example.user.myapplication.ScrollingActivity">
<android.support.design.widget.AppBarLayout
android:id="#+id/app_bar"
android:layout_width="match_parent"
android:layout_height="#dimen/app_bar_height"
android:fitsSystemWindows="true"
android:theme="#style/AppTheme.AppBarOverlay">
<android.support.design.widget.CollapsingToolbarLayout
android:id="#+id/toolbar_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
app:contentScrim="?attr/colorPrimary"
app:layout_scrollFlags="scroll|exitUntilCollapsed|snap">
<android.support.v7.widget.Toolbar
android:id="#+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
app:layout_collapseMode="pin"
app:popupTheme="#style/AppTheme.PopupOverlay"/>
</android.support.design.widget.CollapsingToolbarLayout>
</android.support.design.widget.AppBarLayout>
<android.support.v7.widget.RecyclerView
android:id="#+id/nestedView"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="#string/appbar_scrolling_view_behavior"/>
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal"
app:layout_anchor="#id/app_bar"
app:layout_anchorGravity="bottom|end">
<Button
android:id="#+id/disableNestedScrollingButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="disable"/>
<Button
android:id="#+id/enableNestedScrollingButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="enable"
/>
</LinearLayout>
</android.support.design.widget.CoordinatorLayout>
ScrollingActivity.java
public class ScrollingActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_scrolling);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
final RecyclerView nestedView = (RecyclerView) findViewById(R.id.nestedView);
findViewById(R.id.disableNestedScrollingButton).setOnClickListener(new OnClickListener() {
#Override
public void onClick(final View v) {
nestedView.setNestedScrollingEnabled(false);
}
});
findViewById(R.id.enableNestedScrollingButton).setOnClickListener(new OnClickListener() {
#Override
public void onClick(final View v) {
nestedView.setNestedScrollingEnabled(true);
}
});
nestedView.setLayoutManager(new LinearLayoutManager(this));
nestedView.setAdapter(new Adapter() {
#Override
public ViewHolder onCreateViewHolder(final ViewGroup parent, final int viewType) {
return new ViewHolder(LayoutInflater.from(parent.getContext()).inflate(
android.R.layout.simple_list_item_1,
parent,
false)) {
};
}
#Override
public void onBindViewHolder(final ViewHolder holder, final int position) {
((TextView) holder.itemView.findViewById(android.R.id.text1)).setText("item " + position);
}
#Override
public int getItemCount() {
return 100;
}
});
}
}
What I've tried
At first I thought it's because of something else (I thought it's a weird combination with DrawerLayout), but then I've found a minimal sample to show it, and it's just as I thought: it's all because of the setNestedScrollingEnabled.
I tried to report about this on Google's website (here), hoping it will get fixed if it's a real bug. If you wish to try it out, or watch the videos of the issue, go there, as I can't upload them all here (too large and too many files).
I've also tried to use special flags as instructed on other posts (examples: here, here, here, here and here) , but none helped. In fact each of them had an issue, whether it's staying in expanded mode, or scrolling in a different way than what I do.
The questions
Is this a known issue? Why does it happen?
Is there a way to overcome this?
Is there perhaps an alternative to calling this function of setNestedScrollingEnabled ? One without any issues of scrolling or locking the state of the CollapsingToolbarLayout ?

This is an alternate approach to achieving the same goal as this answer. While that answer used Reflection, this answer does not, but the reasoning remains the same.
Why is this happening?
The problem is that RecyclerView sometimes uses a stale value for the member variable mScrollOffset. mScrollOffset is set in only two places in RecyclerView: dispatchNestedPreScroll and dispatchNestedScroll. We are only concerned with dispatchNestedPreScroll. This method is invoked by RecyclerView#onTouchEvent when it handles MotionEvent.ACTION_MOVE events.
The following is from the documentation for dispatchNestedPreScroll.
dispatchNestedPreScroll
boolean dispatchNestedPreScroll (int dx,
int dy,
int[] consumed,
int[] offsetInWindow)
Dispatch one step of a nested scroll in progress before this view consumes any portion of it.
Nested pre-scroll events are to nested scroll events what touch intercept is to touch. dispatchNestedPreScroll offers an opportunity for the parent view in a nested scrolling operation to consume some or all of the scroll operation before the child view consumes it.
...
offsetInWindow int: Optional. If not null, on return this will contain the offset in local view coordinates of this view from before this operation to after it completes. View implementations may use this to adjust expected input coordinate tracking.
offsetInWindow is actually an int[2] with the second index representing the y shift to be applied to the RecyclerView due to nested scrolling.
RecyclerView#DispatchNestedPrescroll resolves to a method with the same name in NestedScrollingChildHelper.
When RecyclerView calls dispatchNestedPreScroll,
mScrollOffset is used as the offsetInWindow argument. So any changes made to offsetInWindow directly updates mScrollOffset. dispatchNestedPreScroll updates mScrollOffset as long as nested scrolling is in effect. If nested scrolling is not in effect, then mScrollOffset is not updated and proceeds with the value that was last set by dispatchNestedPreScroll. Thus, when nested scrolling is turned off, the value of mScrollOffset becomes immediately stale but RecyclerView continues to use it.
The correct value of mScrollOffset[1] upon return from dispatchNestedPreScroll is the amount to adjust for input coordinate tracking (see above). In RecyclerView the following lines adjusts the y touch coordinate:
mLastTouchY = y - mScrollOffset[1];
If mScrollOffset[1] is, let's say, -30 (because it is stale and should be zero) then mLastTouchY will be off by +30 pixels (--30=+30). The effect of this miscalculation is that it will appear that the touch occurred further down the screen than it really did. So, a slow downward scroll will actually scrolls up and an upward scroll will scroll faster. (If a downward scroll is fast enough to overcome this 30px barrier, then downward scrolling will occur but more slowly than it should.) Upward scrolling will be overly quick since the app thinks more space has been covered.
mScrollOffset will continue as a stale variable until nested scrolling is turned on and dispatchNestedPreScroll once again reports the correct value in mScrollOffset.
Approach
Since mScrollOffset[1] has a stale value under certain circumstances, the goal is to set it to the correct value under those circumstances. This value should be zero when nested scrolling is not taking place, i.e., When the AppBar is expanded or collapsed. Unfortunately, mScrollOffset is local to RecyclerView and there is no setter for it. To gain access to mScrollOffset without resorting to Reflection, a custom RecyclerView is created that overrides dispatchNestedPreScroll. The fourth agument is offsetInWindow which is the variable we need to change.
A stale mScrollOffset occurs whenever nested scrolling is disabled for the RecyclerView. An additional condition we will impose is that the AppBar must be idle so we can safely say that mScrollOffset[1] should be zero. This is not an issue since the CollapsingToolbarLayout specifies snap in the scroll flags.
In the sample app, ScrollingActivity has been modified to record when the AppBar is expanded and closed. A callback has also been created (clampPrescrollOffsetListener) that will return true when our two conditions are met. Our overridden dispatchNestedPreScroll will invoke this callback and clamp mScrollOffset[1] to zero on a true response.
The updated source file for ScrollingActivity is presented below as is the custom RecyclerView - MyRecyclerView.
The XML layout file must be changed to reflect the custom MyRecyclerView.
ScrollingActivity
public class ScrollingActivity extends AppCompatActivity
implements MyRecyclerView.OnClampPrescrollOffsetListener {
private CollapsingToolbarLayout mCollapsingToolbarLayout;
private AppBarLayout mAppBarLayout;
private MyRecyclerView mNestedView;
// This variable will be true when the app bar is completely open or completely collapsed.
private boolean mAppBarIdle = true;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_scrolling);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
mNestedView = (MyRecyclerView) findViewById(R.id.nestedView);
mAppBarLayout = (AppBarLayout) findViewById(R.id.app_bar);
mCollapsingToolbarLayout = (CollapsingToolbarLayout) findViewById(R.id.toolbar_layout);
// Set the listener for the patch code.
mNestedView.setOnClampPrescrollOffsetListener(this);
// Listener to determine when the app bar is collapsed or fully open (idle).
mAppBarLayout.addOnOffsetChangedListener(new AppBarLayout.OnOffsetChangedListener() {
#Override
public final void onOffsetChanged(AppBarLayout appBarLayout, int verticalOffset) {
mAppBarIdle = verticalOffset == 0
|| verticalOffset <= appBarLayout.getTotalScrollRange();
}
});
findViewById(R.id.disableNestedScrollingButton).setOnClickListener(new OnClickListener() {
#Override
public void onClick(final View v) {
// If the AppBar is fully expanded or fully collapsed (idle), then disable
// expansion and apply the patch; otherwise, set a flag to disable the expansion
// and apply the patch when the AppBar is idle.
setExpandEnabled(false);
}
});
findViewById(R.id.enableNestedScrollingButton).setOnClickListener(new OnClickListener() {
#Override
public void onClick(final View v) {
setExpandEnabled(true);
}
});
mNestedView.setLayoutManager(new LinearLayoutManager(this));
mNestedView.setAdapter(new Adapter() {
#Override
public ViewHolder onCreateViewHolder(final ViewGroup parent, final int viewType) {
return new ViewHolder(LayoutInflater.from(parent.getContext()).inflate(
android.R.layout.simple_list_item_1,
parent,
false)) {
};
}
#Override
public void onBindViewHolder(final ViewHolder holder, final int position) {
((TextView) holder.itemView.findViewById(android.R.id.text1)).setText("item " + position);
}
#Override
public int getItemCount() {
return 100;
}
});
}
private void setExpandEnabled(boolean enabled) {
mNestedView.setNestedScrollingEnabled(enabled);
}
// Return "true" when the app bar is idle and nested scrolling is disabled. This is a signal
// to the custom RecyclerView to clamp the y prescroll offset to zero.
#Override
public boolean clampPrescrollOffsetListener() {
return mAppBarIdle && !mNestedView.isNestedScrollingEnabled();
}
private static final String TAG = "ScrollingActivity";
}
MyRecyclerView
public class MyRecyclerView extends RecyclerView {
private OnClampPrescrollOffsetListener mPatchListener;
public MyRecyclerView(Context context) {
super(context);
}
public MyRecyclerView(Context context, AttributeSet attrs) {
super(context, attrs);
}
public MyRecyclerView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}
// Just a call to super plus code to force offsetInWindow[1] to zero if the patchlistener
// instructs it.
#Override
public boolean dispatchNestedPreScroll(int dx, int dy, int[] consumed, int[] offsetInWindow) {
boolean returnValue;
int currentOffset;
returnValue = super.dispatchNestedPreScroll(dx, dy, consumed, offsetInWindow);
currentOffset = offsetInWindow[1];
Log.d(TAG, "<<<<dispatchNestedPreScroll: " + currentOffset);
if (mPatchListener.clampPrescrollOffsetListener() && offsetInWindow[1] != 0) {
Log.d(TAG, "<<<<dispatchNestedPreScroll: " + currentOffset + " -> 0");
offsetInWindow[1] = 0;
}
return returnValue;
}
public void setOnClampPrescrollOffsetListener(OnClampPrescrollOffsetListener patchListener) {
mPatchListener = patchListener;
}
public interface OnClampPrescrollOffsetListener {
boolean clampPrescrollOffsetListener();
}
private static final String TAG = "MyRecyclerView";
}

Actually, you might be looking at the problem in the wrong way.
The only thing you need is to set the Toolbar flags accordingly. You don't really anything else so I would say that your layout should be simplified to:
<android.support.design.widget.CoordinatorLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context="com.example.user.myapplication.ScrollingActivity">
<android.support.design.widget.AppBarLayout
android:id="#+id/app_bar"
android:layout_width="match_parent"
android:layout_height="#dimen/app_bar_height"
android:fitsSystemWindows="true"
android:theme="#style/AppTheme.AppBarOverlay">
<android.support.v7.widget.Toolbar
android:id="#+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
app:layout_scrollFlags="scroll|enterAlways"
app:popupTheme="#style/AppTheme.PopupOverlay"
app:title="Title" />
</android.support.design.widget.AppBarLayout>
<android.support.v7.widget.RecyclerView
android:id="#+id/nestedView"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="#string/appbar_scrolling_view_behavior"/>
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal"
app:layout_anchor="#id/app_bar"
app:layout_anchorGravity="bottom|end">
<Button
android:id="#+id/disableNestedScrollingButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="disable"/>
<Button
android:id="#+id/enableNestedScrollingButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="enable"
/>
</LinearLayout>
</android.support.design.widget.CoordinatorLayout>
Then when you wish to disable the collapsing just set your toolbar flags:
// To disable collapsing
AppBarLayout.LayoutParams params = (AppBarLayout.LayoutParams) toolbar.getLayoutParams();
params.setScrollFlags(AppBarLayout.LayoutParams.SCROLL_FLAG_SNAP);
toolbar.setLayoutParams(params);
And to enable
// To enable collapsing
AppBarLayout.LayoutParams params = (AppBarLayout.LayoutParams) toolbar.getLayoutParams();
params.setScrollFlags(AppBarLayout.LayoutParams.SCROLL_FLAG_SCROLL|AppBarLayout.LayoutParams.SCROLL_FLAG_ENTER_ALWAYS);
toolbar.setLayoutParams(params);
Hold a reference to the layout params if you are changing instead of getting it all the time.
If you need to have the CollapsingToolbarLayout get from and set the LayoutParams to that View instead, update the flags the same way but now adding the appBarLayout.setExpanded(true/false)
Note: Using the setScrollFlags clears all previous flags, so be careful and set all required flags when using this method.

As #Moinkhan points out, you could try wrapping the RecyclerView and next elements in a NestedScrollView like this, this should resolve your problem of scrolling alongside with your collapsing toolbar layout:
<android.support.design.widget.CoordinatorLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context="com.example.user.myapplication.ScrollingActivity">
<android.support.design.widget.AppBarLayout
android:id="#+id/app_bar"
android:layout_width="match_parent"
android:layout_height="#dimen/app_bar_height"
android:fitsSystemWindows="true"
android:theme="#style/AppTheme.AppBarOverlay">
<android.support.design.widget.CollapsingToolbarLayout
android:id="#+id/toolbar_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
app:contentScrim="?attr/colorPrimary"
app:layout_scrollFlags="scroll|exitUntilCollapsed|snap">
<android.support.v7.widget.Toolbar
android:id="#+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
app:layout_collapseMode="pin"
app:popupTheme="#style/AppTheme.PopupOverlay"/>
</android.support.design.widget.CollapsingToolbarLayout>
</android.support.design.widget.AppBarLayout>
<android.support.v4.widget.NestedScrollView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_gravity="fill_vertical"
android:fillViewport="true"
app:layout_behavior="#string/appbar_scrolling_view_behavior">
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<android.support.v7.widget.RecyclerView
android:id="#+id/nestedView"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="#string/appbar_scrolling_view_behavior"/>
</RelativeLayout>
</android.support.v4.widget.NestedScrollView>
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal"
app:layout_anchor="#id/app_bar"
app:layout_anchorGravity="bottom|end">
<Button
android:id="#+id/disableNestedScrollingButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="disable"/>
<Button
android:id="#+id/enableNestedScrollingButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="enable"
/>
</LinearLayout>
</android.support.design.widget.CoordinatorLayout>
In case the contents of the recyclerview are not displayed you can follow this thread to solve that issue How to use RecyclerView inside NestedScrollView?.
Hope it helps.

inside the recycler view, to scrolling smooth
android:nestedScrollingEnabled="false"
to overlap the cardView in the toolbar
app:behavior_overlapTop = "24dp"
Try this code for CollapsingToolbar:
<android.support.design.widget.CoordinatorLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#color/background"
android:fitsSystemWindows="true">
<android.support.design.widget.AppBarLayout
android:id="#+id/app_bar"
android:layout_width="match_parent"
android:layout_height="#dimen/app_bar_height"
android:fitsSystemWindows="true"
android:theme="#style/AppTheme.AppBarOverlay">
<android.support.design.widget.CollapsingToolbarLayout
android:id="#+id/toolbar_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
app:contentScrim="?attr/colorPrimary"
app:layout_scrollFlags="scroll|exitUntilCollapsed">
<android.support.v7.widget.Toolbar
android:id="#+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
app:layout_collapseMode="pin"
app:popupTheme="#style/AppTheme.PopupOverlay"
app:title="Title" />
</android.support.design.widget.CollapsingToolbarLayout>
</android.support.design.widget.AppBarLayout>
<android.support.v4.widget.NestedScrollView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginLeft="10dp"
android:layout_marginRight="10dp"
android:background="#android:color/transparent"
app:behavior_overlapTop="#dimen/behavior_overlap_top"
app:layout_behavior="#string/appbar_scrolling_view_behavior">
<LinearLayout
android:id="#+id/linearLayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<android.support.v7.widget.RecyclerView
android:id="#+id/recycler_view
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="#dimen/text_min_padding"
android:nestedScrollingEnabled="false"
android:scrollbarSize="2dp"
android:scrollbarStyle="outsideInset"
android:scrollbarThumbVertical="#color/colorAccent"
android:scrollbars="vertical" />
</LinearLayout>
</android.support.v4.widget.NestedScrollView>
</android.support.design.widget.CoordinatorLayout>
Screenshot

I had to solve a similar issue and did it using a custom behaviour on the AppBarLayout. Everything works great.
By overriding onStartNestedScroll in the custom behaviour it is possible to block to collapsing toolbar layout from expanding or collapsing while keeping the scroll view (NestedScrollView) in my case, working as expected. I explained the details here, hope it helps.
private class AppBarLayoutBehavior : AppBarLayout.Behavior() {
var canDrag = true
var acceptsNestedScroll = true
init {
setDragCallback(object : AppBarLayout.Behavior.DragCallback() {
override fun canDrag(appBarLayout: AppBarLayout): Boolean {
// Allow/Do not allow dragging down/up to expand/collapse the layout
return canDrag
}
})
}
override fun onStartNestedScroll(parent: CoordinatorLayout,
child: AppBarLayout,
directTargetChild: View,
target: View,
nestedScrollAxes: Int,
type: Int): Boolean {
// Refuse/Accept any nested scroll event
return acceptsNestedScroll
}}

Use following code, it works fine for me:
lockAppBarClosed();
ViewCompat.setNestedScrollingEnabled(recyclerView, false); // to lock the CollapsingToolbarLayout
and implement the following methods:
private void setAppBarDragging(final boolean isEnabled) {
CoordinatorLayout.LayoutParams params =
(CoordinatorLayout.LayoutParams) appBarLayout.getLayoutParams();
AppBarLayout.Behavior behavior = new AppBarLayout.Behavior();
behavior.setDragCallback(new AppBarLayout.Behavior.DragCallback() {
#Override
public boolean canDrag(AppBarLayout appBarLayout) {
return isEnabled;
}
});
params.setBehavior(behavior);
}
public void unlockAppBarOpen() {
appBarLayout.setExpanded(true, false);
appBarLayout.setActivated(true);
setAppBarDragging(false);
}
public void lockAppBarClosed() {
appBarLayout.setExpanded(false, false);
appBarLayout.setActivated(false);
setAppBarDragging(false);
}

I believe that this problem is related to the collapsing toolbar snapping into place (either closed or open) and leaving a vertical offset variable (mScrollOffset[1] in RecyclerView) with a non-zero value that subsequently biases the scroll - slowing or reversing the scroll in one direction and speeding it up in the other. This variable only seems to be set in NestedScrollingChildHelper if nested scrolling is enabled. So, whatever value mScrollOffset[1] has goes unchanged once nest scrolling is disabled.
To reliably reproduce this issue, you can cause the toolbar to snap into place then immediately click disable. See this video for a demonstration. I believe, that the magnitude of the issue varies by how much "snapping" occurs.
If I drag the toolbar to the fully open or closed position and don't let it "snap", then I have not been able to reproduce this problem and mScrollOffset[1] is set to zero which I think is the right value. I have also reproduced the problem by removing snap from the layout_scrollFlags of the collapsing toolbar in the layout and placing the toolbar in a partially open state.
If you want to play around with this, you can put your demo app into debug mode and observe the value of mScrollOffset[1] in RecyclerView#onTouchEvent. Also take a look at NestedScrollingChildHelper's dispatchNestedScroll and dispatchNestedPreScroll methods to see how the offset is set only when nested scrolling is enabled.
So, how to fix this? mScrollOffset is private toRecyclerView and it is not immediately obvious how to subclass anything to change the value of mScrollOffset[1]. That would leave Reflection, but that may not be desirable to you. Maybe another reader has an idea about how to approach this or knows of some secret sauce. I will repost if anything occurs to me.
Edit: I have provided a new ScrollingActivity.java class that overcomes this issue. It does use reflection and applies a patch to set mScrollOffset[1] of RecyclerView to zero when the disable scroll button has been pressed and the AppBar is idle. I have done some preliminary testing and it is working. Here is the gist. (See updated gist below.)
Second edit: I was able to get the toolbar to snap in funny ways and get stuck in the middle without the patch, so it doesn't look like the patch is causing that particular issue. I can get the toolbar to bounce from fully open to collapsed by scrolling down fast enough in the unpatched app.
I also took another look at what the patch is doing and I think that it will behave itself: The variable is private and referred to only in one place after scrolling is turned off. With scrolling enabled, the variable is always reset before use. The real answer is for Google to fix this problem. Until they do, I think this may be the closest you can get to an acceptable work-around with this particular design. (I have posted an updated gist that addresses potential issues with a quick click-around leaving switches in a potential unsuitable state.)
Regardless, the underlying issue has been identified and you have a reliable way to reproduce the problem, so you can more easily verify other proposed solutions.
I hope this helps.

I want to present a nice alternative, mainly based on the one here :
AppBarLayoutEx.kt
class AppBarLayoutEx : AppBarLayout {
private var isAppBarExpanded = true
private val behavior = AppBarLayoutBehavior()
private var onStateChangedListener: (Boolean) -> Unit = {}
var enableExpandAndCollapseByDraggingToolbar: Boolean
get() = behavior.canDrag
set(value) {
behavior.canDrag = value
}
var enableExpandAndCollapseByDraggingContent: Boolean
get() = behavior.acceptsNestedScroll
set(value) {
behavior.acceptsNestedScroll = value
}
constructor(context: Context) : super(context)
constructor(context: Context, attrs: AttributeSet) : super(context, attrs)
init {
addOnOffsetChangedListener(
AppBarLayout.OnOffsetChangedListener { _, verticalOffset ->
isAppBarExpanded = verticalOffset == 0
onStateChangedListener(isAppBarExpanded)
})
}
override fun setLayoutParams(params: ViewGroup.LayoutParams?) {
super.setLayoutParams(params)
(params as CoordinatorLayout.LayoutParams).behavior = behavior
}
fun toggleExpandedState() {
setExpanded(!isAppBarExpanded, true)
}
fun setOnExpandAndCollapseListener(onStateChangedListener: (Boolean) -> Unit) {
this.onStateChangedListener = onStateChangedListener
}
private class AppBarLayoutBehavior : AppBarLayout.Behavior() {
var canDrag = true
var acceptsNestedScroll = true
init {
setDragCallback(object : AppBarLayout.Behavior.DragCallback() {
override fun canDrag(appBarLayout: AppBarLayout) = canDrag
})
}
override fun onStartNestedScroll(parent: CoordinatorLayout, child: AppBarLayout, directTargetChild: View,
target: View, nestedScrollAxes: Int, type: Int) = acceptsNestedScroll
}
}
Usage: besides using it in the layout XML file, you can disable/enable the expanding of it using:
appBarLayout.enableExpandAndCollapseByDraggingToolbar = true/false
appBarLayout.enableExpandAndCollapseByDraggingContent = true/false

Change viewpager and viewpager item size dynamically with listview scroll

I have a listview below a viewpager and in the initial state (when nothing has been scrolled), the viewpager shows only one item with a 10dp "preview" of the next and previous items (I have achieved this by setting a negative page margin:viewPager.setPageMargin(-48);). What I am trying to do is, on scrolling down the listview:
1) the listview should "push" the viewpager up, decreasing its height up to a certain point. On reaching that point (some minHeight for the viewpager), the listview should scroll normally with the smaller sized viewpager above it.
2) The next and the previous items in the viewpager should pull inside (towards the central item) and in the final state, three items of the viewpager should be fully displayed. (Images below to illustrate this)
Scrolling up the listview should do the opposite.
I have managed to do part (1) of my task. Here's the code
My viewpager and listview are inside a FrameLayout like this:
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:showIn="#layout/activity_main" tools:context=".MainActivity">
<ListView
android:id="#+id/listView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:dividerHeight="1dp"
android:divider="#000000"
android:scrollbars="none" />
<android.support.v4.view.ViewPager
android:id="#+id/pager"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:clipToPadding="false"
android:background="#FFFFFF"/>
</FrameLayout>
I "fake" the listview to be below the viewpager by adding a transaprent header view to the listview and making the heights of both the headeview and the viewpager same. Here's a snippet of the code:
screenWidth = // Screen width of the phone
headerHeight = // Required height of the viewpager and the headerview
headerView = inflater.inflate(R.layout.fake_list_header, listView, false);
headerView.getLayoutParams().height = headerHeight;
headerView.getLayoutParams().width = screenWidth;
viewPager.getLayoutParams().height = headerHeight;
viewPager.getLayoutParams().width = screenWidth;
viewPager.setPageMargin(negativeMargin);
listView.addHeaderView(headerView, null, false);
// Other initializations and stuff
fake_list_header layout file:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">
<FrameLayout
android:layout_width="match_parent"
android:layout_height="match_parent" />
</LinearLayout>
Finally, my listview OnScrollListener that takes care of adjusting the viewpager height depending on the amount scrolled by the listview and stopping when we reach the minimum height for the viewpager:
OnScrollListener() {
#Override
public void onScrollStateChanged(AbsListView absListView, int i) {
}
#Override
public void onScroll(AbsListView absListView, int i, int i1, int i2) {
if (listview.getFirstVisiblePosition() == 0) {
View firstChild = listview.getChildAt(1); // 0th element is the fake headerview itself
int topY = 0;
if (firstChild != null) {
topY = firstChild.getTop();
FrameLayout.LayoutParams layoutParams = new FrameLayout.LayoutParams(
RelativeLayout.LayoutParams.MATCH_PARENT,
RelativeLayout.LayoutParams.WRAP_CONTENT);
layoutParams.width = screenWidth;
layoutParams.height = topY;
if (topY < headerHeight && topY >= minHeight) {
// minHeight is the minimum height the viewpager takes, after this point it stops getting smaller
//And vice-versa with headerHeight taking care of the maximum height the viewpager can take
viewpager.setLayoutParams(layoutParams);
}
}
}
}
}
Part (2) of my task is where I am stuck (and running out of ideas), I have tried changing pageMargin of the viewpager with the scroll but the results aren't good (also don't think it is the right approach for achieving something like this). Setting X position of the next(or previous) view in the pager by calling setTranslationX with scroll also isn't working.
Here are some mocks of what I am trying to achieve:
Initial state (nothing scrolled)
Final state (minHeight of viewpager achieved)
Is using viewpager and a listview right way of achieving something like this? I thought of using a horizontal recyclerview instead of a viewpager, but I need the "page by page" scroll behavior of a viewpager for the horizontal scroll/swipe of items. Any suggestions welcome

Try this in your main layout
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:showIn="#layout/activity_main" tools:context=".MainActivity">
<ListView
android:id="#+id/listView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:dividerHeight="1dp"
android:layout_below="#+id/pager"
android:divider="#000000"
android:scrollbars="none" />
<android.support.v4.view.ViewPager
android:id="#+id/pager"
android:layout_width="match_parent"
android:layout_height="150dp"
android:clipToPadding="false"
android:background="#FFFFFF"/>
</RelativeLayout>

Hiding AppBarLayout and giving its space to the remaining view

I have a pretty standard layout using the new design libraries:
<AppBarLayout>
<CollapsingToolbarLayout>
<ImageView/>
<Toolbar/>
</CollapsingToolbarLayout>
</AppBarLayout>
<android.support.v4.widget.NestedScrollView/> <!-- content here -->
What I'm trying to do is to completely hide the whole AppBarLayout programmatically, to temporarily get rid of the Toolbar and its collapsing feature.
So I'm calling this:
private void disableCollapsing() {
AppBarLayout.LayoutParams p = (AppBarLayout.LayoutParams) collapsingToolbarLayout.getLayoutParams();
p.setScrollFlags(0);
collapsingToolbarLayout.setLayoutParams(p);
}
to disable the collapsing behavior (works well), and finally this:
#Override
public void hide() {
final AppBarLayout layout = (AppBarLayout) findViewById(R.id.appbar);
layout.animate().translationY(-layout.getHeight())
.setListener(new AnimatorListenerAdapter() {
#Override
public void onAnimationEnd(Animator animation) {
super.onAnimationEnd(animation);
layout.setVisibility(View.GONE);
}
}).start();
}
I make the AppBarLayout translate to the top (works smoothly), and at the end of the animation set is visibility to View.GONE.
Issue
At the end of the animation, no matter I also set the visibility to GONE, I can't get the space that was previously occupied by the AppBarLayout. My NestedScrollView remains confined in the lower half of the screen, as if the AppBarLayout was still there (which is not). How can I fix it?
Before hiding:
After hiding (AppBar translated to the top):
As you can see, the top space is empty and unreachable. The scroll view scrolls inside the margins it had before, as if the visibility change was not measured by the CoordinatorLayout.
I have tried calling coordinator.requestLayout(), with no success.
I also tried setting the AppBarLayout as an app:anchor for my NestedScrollView, but that screws things up - scroll view ends up taking the whole screen even before hiding.
I was thinking of a custom Behavior to be set on the scroll view when entering this hidden-AppBar mode, but I can't get started on that.

Yes this looks like a bug, I solved this issue for my application setting the appbar height to 0:
android.support.design.widget.AppBarLayout appbar = (android.support.design.widget.AppBarLayout) findViewById(R.id.appbar);
CoordinatorLayout.LayoutParams lp = (CoordinatorLayout.LayoutParams)appbar.getLayoutParams();
lp.height = 0;
appbar.setLayoutParams(lp);

As mentioned above, setting the Coordinator.LayoutParams#height fixes the issue.
However, I wanted to express how/when this occurs (not necessarily why):
The CollaspingToolbarLayout will exhibit this behavior only when its app:layout_scrollFlags property is set to exitUntilCollapsed and its nested ToolBar also has defines app:layout_collapseMode="pin". With this combination of flags, the Toolbar will pin itself to the top of the screen, and this is intentional and sometimes desirable.
(snipped for brevity)
<androidx.coordinatorlayout.widget.CoordinatorLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent">
<com.google.android.material.appbar.AppBarLayout
android:id="#+id/appbar"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<com.google.android.material.appbar.CollapsingToolbarLayout
android:id="#+id/collapsingToolbar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:layout_scrollFlags="scroll|exitUntilCollapsed">
<!-- some other component here, i.e ImageView -->
<androidx.appcompat.widget.Toolbar
android:id="#+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:gravity="top"
app:layout_collapseMode="pin" />
</com.google.android.material.appbar.CollapsingToolbarLayout>
</com.google.android.material.appbar.AppBarLayout>
<!-- some scrolling view/layout -->
</androidx.coordinatorlayout.widget.CoordinatorLayout>
In the Fragment/Activity after the view is created, in Kotlin + ViewBinding:
binding.appbar.updateLayoutParams<CoordinatorLayout.LayoutParams> {
height = 0
}
For me, I had to capture the height of the AppBarLayout before hiding it to restore it to its original height when I wanted to show it.
private var appbarLayoutHeight = 0
private fun hideAppBar() {
appbarLayoutHeight = binding.appbar.measuredHeight
binding.appbar.updateLayoutParams<CoordinatorLayout.LayoutParams> {
height = 0
}
}
private fun showAppBar() {
binding.appbar.updateLayoutParams<CoordinatorLayout.LayoutParams> {
height = appbarLayoutHeight
}
}
Disclaimer: ViewBinding is not necessary to achieve this, nor is using Kotlin, and it's just what I use to acquire the AppBarLayoout and make this as terse/sugary as possible.

This works for me. Just toggles appbar on/off.
private boolean hide = true;
public void toggleAppBar() {
// Calculate ActionBar height
TypedValue tv = new TypedValue();
int actionBarHeight = 0;
if (getTheme().resolveAttribute(android.R.attr.actionBarSize, tv, true)) {
actionBarHeight = TypedValue.complexToDimensionPixelSize(tv.data, getResources().getDisplayMetrics());
}
CoordinatorLayout.LayoutParams lp = (CoordinatorLayout.LayoutParams)appBarLayout.getLayoutParams();
lp.height = hide ? 0 : actionBarHeight;
appBarLayout.setLayoutParams(lp);
appBarLayout.setExpanded(!hide, true);
hide = !hide;
appbar_layout.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<com.google.android.material.appbar.AppBarLayout
android:id="#+id/appBarLayout"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="#style/AppTheme.AppBarOverlay">
<androidx.appcompat.widget.Toolbar
android:id="#+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary"
app:popupTheme="#style/AppTheme.PopupOverlay" />
</com.google.android.material.appbar.AppBarLayout>
<include layout="#layout/content_main" />
</androidx.coordinatorlayout.widget.CoordinatorLayout>

Thanks #Caleb Kleveter that is my code for Kotlin
val appBarLayout = activity?.findViewById<AppBarLayout>(R.id.app_bar_layout)
val lp = appBarLayout?.layoutParams
lp?.height = 0;
appBarLayout?.layoutParams = lp

The following works as well
appBarLayout.setExpanded(false, false);
appBarLayout.setVisibility(View.GONE);

How do the animation hiding the ActionBar and keeping tabs?

In version 5 of Google Play Store app, scroll to the content, ActionBar on with scrolling, but the tabs are fixed to get on top.
How to do this?
BEFORE SCROLL
AFTER SCROLL

As others have suggested, use ObservableScrollView from: https://github.com/ksoichiro/Android-ObservableScrollView
Try putting both the Toolbar and the SlidingTabStrip in the same container, then animate that container as the user scrolls the ObservableScrollView, for example:
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<com.github.ksoichiro.android.observablescrollview.ObservableListView
android:id="#+id/listView"
android:layout_height="match_parent"
android:layout_width="match_parent"/>
<LinearLayout
android:id="#+id/toolbarContainer"
android:orientation="vertical"
android:elevation="10dp"
android:background="#color/material_deep_teal_200"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<android.support.v7.widget.Toolbar
android:id="#+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"/>
<!--Placeholder view, your tabstrip goes here-->
<View
android:layout_width="wrap_content"
android:layout_height="48dp"/>
</LinearLayout>
</FrameLayout>
Then when you override the ObservableScrollViewCallbacks you could do something like this:
#Override
public void onScrollChanged(int scrollY, boolean firstScroll, boolean dragging) {
toolbarContainer.animate().cancel();
int scrollDelta = scrollY - oldScrollY;
oldScrollY = scrollY;
float currentYTranslation = -toolbarContainer.getTranslationY();
float targetYTranslation = Math.min(Math.max(currentYTranslation + scrollDelta, 0), toolbarHeight);
toolbarContainer.setTranslationY(-targetYTranslation);
}
#Override
public void onUpOrCancelMotionEvent(ScrollState scrollState) {
float currentYTranslation = -toolbarContainer.getTranslationY();
int currentScroll = listView.getCurrentScrollY();
if (currentScroll < toolbarHeight) {
toolbarContainer.animate().translationY(0);
} else if (currentYTranslation > toolbarHeight /2) {
toolbarContainer.animate().translationY(-toolbarHeight);
} else {
toolbarContainer.animate().translationY(0);
}
}
The onUpOrCancelMotionEvent stuff is to animate the container to prevent the toolbar from being only half shown/hidden.
Here's a demo video just for reference: https://drive.google.com/file/d/0B7TH7VeIpgSQSzZER1NneWpYa1E/view?usp=sharing

Answer is here:
https://github.com/ksoichiro/Android-ObservableScrollView :D
This library is excellent for my case and very others

Great that you answer your question by yourself ;)
Here is another small hint:
Use a seperated layout for your tabs or integrate them into your toolbar and then tranlsate the toolbar only as far as you can see the tabs on top.

Expand/Collapse Lollipop toolbar animation (Telegram app)

I'm trying to figure out how the expand/collapse animation of the toolbar is done. If you have a look at the Telegram app settings, you will see that there is a listview and the toolbar. When you scroll down, the toolbar collapse, and when you scroll up it expands. There is also the animation of the profile pic and the FAB. Does anyone have any clue on that? Do you think they built all the animations on top of it? Maybe I'm missing something from the new APIs or the support library.
I noticed the same behaviour on the Google calendar app, when you open the Spinner (I don't think it's a spinner, but it looks like): The toolbar expands and when you scroll up, it collapse.
Just to clearify: I don't need the QuickReturn method. I know that probably Telegram app is using something similar. The exact method that I need is the Google Calendar app effect. I've tried with
android:animateLayoutChanges="true"
and the expand method works pretty well. But obviously, If I scroll up the ListView, the toolbar doesn't collapse.
I've also thought about adding a GestureListener but I want to know if there are any APIs or simpler methods of achieving this.
If there are none, I think I will go with the GestureListener. Hopefully to have a smooth effect of the Animation.
Thanks!

Edit :
Since the release of the Android Design support library, there's an easier solution. Check joaquin's answer
--
Here's how I did it, there probably are many other solutions but this one worked for me.
First of all, you have to use a Toolbar with a transparent background. The expanding & collapsing Toolbar is actually a fake one that's under the transparent Toolbar. (you can see on the first screenshot below - the one with the margins - that this is also how they did it in Telegram).
We only keep the actual Toolbar for the NavigationIcon and the overflow MenuItem.
Everything that's in the red rectangle on the second screenshot (ie the fake Toolbar and the FloatingActionButton) is actually a header that you add to the settings ListView (or ScrollView).
So you have to create a layout for this header in a separate file that could look like this :
<!-- The headerView layout. Includes the fake Toolbar & the FloatingActionButton -->
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<RelativeLayout
android:id="#+id/header_container"
android:layout_width="match_parent"
android:layout_height="#dimen/header_height"
android:layout_marginBottom="3dp"
android:background="#android:color/holo_blue_dark">
<RelativeLayout
android:id="#+id/header_infos_container"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:padding="16dp">
<ImageView
android:id="#+id/header_picture"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerVertical="true"
android:layout_marginRight="8dp"
android:src="#android:drawable/ic_dialog_info" />
<TextView
android:id="#+id/header_title"
style="#style/TextAppearance.AppCompat.Title"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_toRightOf="#+id/header_picture"
android:text="Toolbar Title"
android:textColor="#android:color/white" />
<TextView
android:id="#+id/header_subtitle"
style="#style/TextAppearance.AppCompat.Subhead"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/header_title"
android:layout_toRightOf="#+id/header_picture"
android:text="Toolbar Subtitle"
android:textColor="#android:color/white" />
</RelativeLayout>
</RelativeLayout>
<FloatingActionButton
android:id="#+id/header_fab"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="bottom|right"
android:layout_margin="10dp"
android:src="#drawable/ic_open_in_browser"/>
</FrameLayout>
(Note that you can use negative margins/padding for the fab to be straddling on 2 Views)
Now comes the interesting part. In order to animate the expansion of our fake Toolbar, we implement the ListView onScrollListener.
// The height of your fully expanded header view (same than in the xml layout)
int headerHeight = getResources().getDimensionPixelSize(R.dimen.header_height);
// The height of your fully collapsed header view. Actually the Toolbar height (56dp)
int minHeaderHeight = getResources().getDimensionPixelSize(R.dimen.action_bar_height);
// The left margin of the Toolbar title (according to specs, 72dp)
int toolbarTitleLeftMargin = getResources().getDimensionPixelSize(R.dimen.toolbar_left_margin);
// Added after edit
int minHeaderTranslation;
private ListView listView;
// Header views
private View headerView;
private RelativeLayout headerContainer;
private TextView headerTitle;
private TextView headerSubtitle;
private FloatingActionButton headerFab;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
View rootView = inflater.inflate(R.layout.listview_fragment, container, false);
listView = rootView.findViewById(R.id.listview);
// Init the headerHeight and minHeaderTranslation values
headerHeight = getResources().getDimensionPixelSize(R.dimen.header_height);
minHeaderTranslation = -headerHeight +
getResources().getDimensionPixelOffset(R.dimen.action_bar_height);
// Inflate your header view
headerView = inflater.inflate(R.layout.header_view, listview, false);
// Retrieve the header views
headerContainer = (RelativeLayout) headerView.findViewById(R.id.header_container);
headerTitle = (TextView) headerView.findViewById(R.id.header_title);
headerSubtitle = (TextView) headerView.findViewById(R.id.header_subtitle);
headerFab = (TextView) headerView.findViewById(R.id.header_fab);;
// Add the headerView to your listView
listView.addHeaderView(headerView, null, false);
// Set the onScrollListener
listView.setOnScrollListener(this);
// ...
return rootView;
}
#Override
public void onScrollStateChanged(AbsListView view, int scrollState)
{
// Do nothing
}
#Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount)
{
Integer scrollY = getScrollY(view);
// This will collapse the header when scrolling, until its height reaches
// the toolbar height
headerView.setTranslationY(Math.max(0, scrollY + minHeaderTranslation));
// Scroll ratio (0 <= ratio <= 1).
// The ratio value is 0 when the header is completely expanded,
// 1 when it is completely collapsed
float offset = 1 - Math.max(
(float) (-minHeaderTranslation - scrollY) / -minHeaderTranslation, 0f);
// Now that we have this ratio, we only have to apply translations, scales,
// alpha, etc. to the header views
// For instance, this will move the toolbar title & subtitle on the X axis
// from its original position when the ListView will be completely scrolled
// down, to the Toolbar title position when it will be scrolled up.
headerTitle.setTranslationX(toolbarTitleLeftMargin * offset);
headerSubtitle.setTranslationX(toolbarTitleLeftMargin * offset);
// Or we can make the FAB disappear when the ListView is scrolled
headerFab.setAlpha(1 - offset);
}
// Method that allows us to get the scroll Y position of the ListView
public int getScrollY(AbsListView view)
{
View c = view.getChildAt(0);
if (c == null)
return 0;
int firstVisiblePosition = view.getFirstVisiblePosition();
int top = c.getTop();
int headerHeight = 0;
if (firstVisiblePosition >= 1)
headerHeight = this.headerHeight;
return -top + firstVisiblePosition * c.getHeight() + headerHeight;
}
Note that there are some parts of this code I didn't test, so feel free to highlight mistakes. But overall, I'm know that this solution works, even though I'm sure it can be improved.
EDIT 2:
There were some mistakes in the code above (that I didn't test until today...), so I changed a few lines to make it work :
I introduced another variable, minHeaderTranslation, which replaced minHeaderHeight;
I changed the Y translation value applied to the header View from :
headerView.setTranslationY(Math.max(-scrollY, minHeaderTranslation));
to :
headerView.setTranslationY(Math.max(0, scrollY + minHeaderTranslation));
Previous expression wasn't working at all, I'm sorry about that...
The ratio calculation also changed, so that it now evolves from the bottom the toolbar (instead of the top of the screen) to the full expanded header.

Also check out CollapsingTitleLayout written by Chris Banes in Android team:
https://plus.google.com/+ChrisBanes/posts/J9Fwbc15BHN
Code: https://gist.github.com/chrisbanes/91ac8a20acfbdc410a68

Use design support library http://android-developers.blogspot.in/2015/05/android-design-support-library.html
include this in build.gradle
compile 'com.android.support:design:22.2.0'
compile 'com.android.support:appcompat-v7:22.2.+'
for recycler view include this also
compile 'com.android.support:recyclerview-v7:22.2.0'
<!-- AppBarLayout allows your Toolbar and other views (such as tabs provided by TabLayout)
to react to scroll events in a sibling view marked with a ScrollingViewBehavior.-->
<android.support.design.widget.AppBarLayout
android:id="#+id/appbar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:fitsSystemWindows="true">
<!-- specify tag app:layout_scrollFlags -->
<android.support.v7.widget.Toolbar
android:id="#+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary"
app:layout_scrollFlags="scroll|enterAlways"/>
<!-- specify tag app:layout_scrollFlags -->
<android.support.design.widget.TabLayout
android:id="#+id/tabLayout"
android:scrollbars="horizontal"
android:layout_below="#+id/toolbar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="?attr/colorPrimary"
app:layout_scrollFlags="scroll|enterAlways"/>
<!-- app:layout_collapseMode="pin" will help to pin this view at top when scroll -->
<TextView
android:layout_width="match_parent"
android:layout_height="50dp"
android:text="Title"
android:gravity="center"
app:layout_collapseMode="pin" />
</android.support.design.widget.AppBarLayout>
<!-- This will be your scrolling view.
app:layout_behavior="#string/appbar_scrolling_view_behavior" tag connects this features -->
<android.support.v7.widget.RecyclerView
android:id="#+id/list"
app:layout_behavior="#string/appbar_scrolling_view_behavior"
android:layout_width="match_parent"
android:layout_height="match_parent">
</android.support.v7.widget.RecyclerView>
</android.support.design.widget.CoordinatorLayout>
Your activity should extend AppCompatActivity
public class YourActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.your_layout);
//set toolbar
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
}
}
Your app theme should be like this
<resources>
<!-- Base application theme. -->
<style name="AppTheme" parent="Theme.AppCompat.NoActionBar">
</style>
</resources>

This is my implementation:
collapsedHeaderHeight and expandedHeaderHeight are defined somewhere else, with the function getAnimationProgress I can get the Expand/Collapse progress, base on this value I do my animation and show/hide the real header.
listForumPosts.setOnScrollListener(new AbsListView.OnScrollListener() {
/**
* #return [0,1], 0 means header expanded, 1 means header collapsed
*/
private float getAnimationProgress(AbsListView view, int firstVisibleItem) {
if (firstVisibleItem > 0)
return 1;
// should not exceed 1
return Math.min(
-view.getChildAt(0).getTop() / (float) (expandedHeaderHeight - collapsedHeaderHeight), 1);
}
#Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
// at render beginning, the view could be empty!
if (view.getChildCount() > 0) {
float animationProgress = getAnimationProgress(view, firstVisibleItem);
imgForumHeaderAvatar.setAlpha(1-animationProgress);
if (animationProgress == 1) {
layoutForumHeader.setVisibility(View.VISIBLE);
} else {
layoutForumHeader.setVisibility(View.GONE);
}
}
}
#Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
// do nothing
}
}