Develop Reference

Prevent a child in ScrollView from being scrolled out of the screen

Somehow I came across Reddit app, and wondered how their Scrolling mechanism works. As you can see from the gif, there is a Menubar (Up/Downvote-comment-share bar) that always locates within the screen and can’t be scrolled out of the screen when scrolled up/down. When scrolling up, it will be located underneath the Toolbar (the grey bar at the top). When scrolling down, it will be located above the EditTextView (the Add-a-comment bar at the bottom).
Relative layout
|-->Toolbar (android:id="#+id/toolbar")
|-->ScrollView (android:layout_below="#id/toolbar")
|-->Child (This child is located underneath the Toolbar when scrolling up)
|-->Child
|-->Child
If I wanted to write this page, what dependencies, widgets or concepts
would I need to use or look into?
Note: You can give me snippets of codes if you prefer :)

you can use the CoordinatorLayout layout to realize that function. the layout like that. for details, you can see this blog in the medium.
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="#+id/behavior_demo_coordinatorLayout"
android:layout_width="match_parent"
android:layout_height="match_parent">
<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
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|snap"
android:background="?attr/colorPrimary" />
</android.support.design.widget.AppBarLayout>
<android.support.v4.widget.SwipeRefreshLayout
android:id="#+id/behavior_demo_swipe_refresh"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="#string/appbar_scrolling_view_behavior">
<android.support.v7.widget.RecyclerView
android:id="#+id/behavior_demo_recycler"
android:layout_width="match_parent"
android:layout_height="match_parent"
/>
</android.support.v4.widget.SwipeRefreshLayout>
</android.support.design.widget.CoordinatorLayout>

The toolbar (containing the menu) is outside of the ScrollView in the XML.
Or it may not even be a ScrollView at all.
It may just be view recycling- but even so the toolbar is outside of that XML layout used for displaying the content.

For hiding the TopBar and bottomBar (comment box) I recommend you use Animation
Simply call animation like
//on scrollUp
topLayout.animate().translationY(-300).alpha(0.0f).setDuration(300);
// this will make the layout go up and fade to invisible
//on scrollDown
topLayout.animate().translationY(0).alpha(1.0f).setDuration(300);
// this will make the layout come down and fade to be visible
Implement this will both Views using addOnScrollListener() or I suggest you to have a look at this answer for implementing scroll Up/Down using CoordinateLayout
Hope this will help!

How to trigger a recyclerview scroll listener when it is inside a scroll view?

How to trigger a recyclerview scroll listener when it is inside a scroll view?
Here the scroll view listener is alone triggering

1. Set nested scrolling enabled false of recycler view.
recyclerView.setNestedScrollingEnabled(false);
2. Add scroll listner to nested scrollview.
mScrollView.getViewTreeObserver().addOnScrollChangedListener(new
ViewTreeObserver.OnScrollChangedListener() {
#Override
public void onScrollChanged()
{
View view = (View)mScrollView.getChildAt(mScrollView.getChildCount() - 1);
int diff = (view.getBottom() - (mScrollView.getHeight() + mScrollView
.getScrollY()));
if (diff == 0) {
// your pagination code
}
}
});

Try with NestedScrollView instead of ScrollView.
NestedScrollView is just like ScrollView, but it supports acting as both a nested scrolling parent and child on both new and old versions of Android. Nested scrolling is enabled by default.
Note: You have to set setNestedScrollingEnable(false) to your recylerview.
in xml add android:nestedScrollingEnabled="false" in recyclerview
OR
programmatically yourRecylerview.setNestedScrollingEnabled(false);
See this article.

You can try this one, but still I assuming you may have the same code like mine as you didnot post your needed code into your question.
Try this:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<android.support.v4.widget.NestedScrollView
android:id="#+id/nestedScrollView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:overScrollMode="never">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical">
<android.support.v7.widget.RecyclerView
android:id="#+id/recyclerView"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</LinearLayout>
</android.support.v4.widget.NestedScrollView>
</LinearLayout>
Use NestedScrollView with <android.support.v7.widget.RecyclerView as I have mention above.

Its ScrollListener will not work as all the rows gets layed when recyclerview is inside scrollview whole purpose of recyclerview gets destroyed when you put it inside scroll view.
For Example as the recyclerview will stretch to full fill its parent ,when you will put it inside scroll view , in case of scroll view it will stretch to its fullest. if there are 1000 items in recyclerview all it will draw 1000 different rows which is also a performance issue.
You should remove it from a scroll view to make its scroll listener working

RecyclerView as child of NestedScrollView - not recycling views

I am trying to create a scroll-able area which will contain various sections of the following types:
Horizontal Recycling Section
Vertical Recycling Section
Text Section
The approach I am taking is to have a NestedRecyclerView as the parent scroll view for all the child sections. This view looks like so:
<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto">
<androidx.coordinatorlayout.widget.CoordinatorLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<com.google.android.material.appbar.AppBarLayout
android:id="#+id/mynav_appbarLayout"
android:background="?attr/themeToolbarBg"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<include
android:id="#+id/mynav_toolbar"
layout="#layout/actionbar_toolbar"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</com.google.android.material.appbar.AppBarLayout>
<androidx.core.widget.NestedScrollView
android:id="#+id/nestedScrollView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fillViewport="true"
app:layout_behavior="com.google.android.material.appbar.AppBarLayout$ScrollingViewBehavior">
<LinearLayout
android:id="#+id/content"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"/>
</androidx.core.widget.NestedScrollView>
</androidx.coordinatorlayout.widget.CoordinatorLayout>
</layout>
Then, for each section type I am creating a corresponding view binding and adding it as a child to the LinearLayout which is inside the NestedScrollView.
There are 2 types of section layout, one which is a simple TextView (which I will omit here as it is not relevant) the other of which is a view which contains a RecyclerView. The layout manager for this RecyclerView is created dynamically depending on whether the section it is to be used for is a horizontal or vertical section.
The layout with the RecyclerView in looks like so:
<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto">
<LinearLayout
android:id="#+id/content"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:focusable="true"
android:focusableInTouchMode="true">
<TextView
android:id="#+id/title"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginStart="24dp"
android:layout_marginTop="8dp"/>
<androidx.recyclerview.widget.RecyclerView
android:id="#+id/fooBarsRecycler"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginStart="16dp"
android:layout_marginTop="8dp"
android:nestedScrollingEnabled="false"
app:layout_behavior="com.google.android.material.appbar.AppBarLayout$ScrollingViewBehavior"/>
</LinearLayout>
</layout>
Now, when I am adding these views to the parent NestedScrollView's LinearLayout and setting up the LayoutManager for the associated RecyclerView to orientation Horizontal it works fine, but, when I use orientation Vertical (which is the same orientation as the NestedScrollView) the RecyclerView is NOT recycling views. Obviously this is leading to unacceptable performance.
After doing about a days worth of research and banging my head against the wall it appears that having a RecyclerView nested within a NestedScrollView with the same orientation as the NestedScrollView causes the RecyclerView to lose it's recycler functionality.
As you can hopefully see from the above layout, I have tried all the suggestions I could find, making sure the RecyclerView's height is not wrap_content, using layout_behaviour, setting the NestedRecyclerView to fill view port and so on.
I have exhausted 6 pages of google search around this issue and have tried every suggestion I have found either on SO or blogs and nothing is working.
Oddly, if I swap out the NestedScrollView for a ScrollView, the vertical RecyclerView regains it's recycler functionality, but now scrolls independently of the parent ScrollView which doesn't meet our requirements.
Is this a solved problem or do I need to rethink my entire solution? I.e. am I just missing an attribute or doing something wrong in the XML or is it fundamentally an issue with using a RecyclerView inside a NestedScrollView with the same orientation?
Here is the list of resources, the suggestions of which I have tried exhaustively to no avail:
How to use RecyclerView inside NestedScrollView?
How to use RecyclerView inside NestedScrollView
Recycler view inside NestedScrollView causes scroll to start in the middle
https://android.jlelse.eu/recyclerview-within-nestedscrollview-scrolling-issue-3180b5ad2542
https://medium.com/#mujtahidah/load-more-recyclerview-inside-nested-scroll-view-and-coordinator-layout-4f179dc01fd
https://github.com/google/flexbox-layout/issues/400
https://www.reddit.com/r/androiddev/comments/8oj8cb/having_recyclerview_inside_a_nestedscrollview_is/
https://github.com/mikepenz/FastAdapter/issues/447
https://www.reddit.com/r/androiddev/comments/bixl6r/nestedscrollview_recyclerview/
View Recycling not happens with Multiple Recyclerview inside NestedScrollView
How to make RecyclerView do recycling inside NestedScrollView?
https://code-examples.net/en/q/1d90611
As per a suggestion in the comments, I could model this with a multi type adapter, which is something I have done before but for this particular problem I am not sure this approach will work.
I think the comment is suggesting I model it like so:
Where the adapter would adapt types:
Horizontal Section
Text Section
Card Section
But, the requirement is this:
So, as you can hopefully see, the RecyclerView will have a LinearLayoutManager with orientation Vertical, but, once we hit the cards, they have to be laid out in a grid fashion, which of course the LinearLayoutManager does not support. So, perhaps I can have the final section be another RecyclerView with a GridLayoutManager? But, I tried this last night and it didn't work, there were scrolling issues as the bottom most RecyclerView is scrolling vertically within the outermost RecyclerView which is also scrolling vertically.

Prevent RecyclerView from scrolling under AppBarLayout before AppBarLayout is collapsed

I'm creating a RecyclerView with header where the header collapses as you scroll up the RecyclerView. I can achieve this very closely with the layout below, with a transparent AppBarLayout, and MyCoolView which is the header. The parallax effect works great.
However, if the header is still visible and I fling the RecyclerView, the RV scrolls slowly to the top and some of the items are under the Toolbar until the RV reaches the top of the view. I've been playing around with the scrollFlags but haven't achieved a desirable result. Any suggestions on how to improve the fling experience so the items don't get clipped?
View the video and watch when its flinged --- https://www.dropbox.com/s/jppd6m7zo41k23z/20160609_151309.mp4?dl=0
<android.support.design.widget.CoordinatorLayout>
<android.support.design.widget.AppBarLayout
android:background="#00000000">
<android.support.design.widget.CollapsingToolbarLayout
app:layout_scrollFlags="scroll|exitUntilCollapsed">
<com.android.myapp.MyCoolView
app:layout_collapseMode="parallax"/>
</android.support.design.widget.CollapsingToolbarLayout>
</android.support.design.widget.AppBarLayout>
<android.support.v7.widget.RecyclerView/>
</android.support.design.widget.CoordinatorLayout>

Possible solution (untested). Add an OnOffsetChangedListener to your AppBarLayout, and keep note of the offset value. First, declare this field:
private boolean shouldScroll = false;
Then, onCreate:
AppBarLayout appbar = findViewById(...);
appbar.addOnOffsetChangedListener(new OnOffsetChangedListener() {
#Override
void onOffsetChanged(AppBarLayout appbar, int offset) {
// Allow recycler scrolling only if we started collapsing.
this.shouldScroll = offset != 0;
}
});
Now, add a scroll listener to your RecyclerView. Whenever it tries to scroll, revert the scroll if the AppBarLayout is still expanded:
RecyclerView recycler = findViewById(...);
recycler.addOnScrollListener(new OnScrollListener() {
#Override
void onScrolled(RecyclerView recycler, int dx, int dy) {
// If AppBar is fully expanded, revert the scroll.
if (!shouldScroll) {
recycler.scrollTo(0,0);
}
}
});
This might need some tweaking though. I see two issues:
Possible stack overflow if scrollTo() calls onScrolled() back. Can be solved with a boolean or by removing/adding the scroll listener
Possibly you want to prevent scrolling not only when AppBarLayout is fully expanded, but more generally when AppBarLayout is not collapsed. This means you don’t have to check for offset != 0, but rather for offset == appBarLayout.getTotalScrollRange(). I think.

Maybe you can add layout_behavior="#string/appbar_scrolling_view_behavior" to your RecylerView like this.
<android.support.v7.widget.RecyclerView
android:layout_width="match_parent"
android:layout_height="match_parent" app:layout_behavior="#string/appbar_scrolling_view_behavior" />

Wrapping the RecyclerView in a FrameLayout solves this problem.
You also need move the appbar_scrolling_view_behavior from the RecyclerView to the FrameLayout so it will be positioned below the AppBarLayout properly.
<android.support.design.widget.CoordinatorLayout>
<android.support.design.widget.AppBarLayout
android:background="#00000000">
<android.support.design.widget.CollapsingToolbarLayout
app:layout_scrollFlags="scroll|exitUntilCollapsed">
<com.android.myapp.MyCoolView
app:layout_collapseMode="parallax"/>
</android.support.design.widget.CollapsingToolbarLayout>
</android.support.design.widget.AppBarLayout>
<!-- BEGIN SOLUTION -->
<!-- the layout behavior needs to be set on the FrameLayout, not the RecyclerView -->
<FrameLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="#string/appbar_scrolling_view_behavior"
>
<!--This RecyclerView MUST be wrapped in a FrameLayout-->
<!--This prevents the RecyclerView from going behind the AppBarLayout-->
<android.support.v7.widget.RecyclerView
android:layout_width="match_parent"
android:layout_height="match_parent"
/>
</FrameLayout>
<!-- END SOLUTION -->
</android.support.design.widget.CoordinatorLayout>

NestedScrollView (NSV) in CoordinatorLayout (CL): NSV Not at Top When Loaded

I am using an NSV in a CL for the ability to have the toolbar compress when the NSV scrolls down. The problem that I am having is that my NSV is not scrolled to the top when it loads, instead, it is offset from the top of the NSV by quite a margin (I am not certain where this spacing is coming from, it's not in the layout).
Please take a look at the screen captures, the first one shows how the NSV loads and you can clearly see the NSV has scrolled down quite a bit from the top by comparing the second (when I scroll the NSV to the top manually):
I did some updates to this layout and it caused this to occur, previously, it loaded at the top without issue. However, I did not add any spacing that should have caused this.
Here is the layout I'm using for this:
<android.support.design.widget.CoordinatorLayout
android:id="#+id/cl_goal_detail"
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="0dp"
android:layout_weight="1">
<android.support.design.widget.AppBarLayout
android:id="#+id/abl_goal_detail"
android:layout_width="match_parent"
android:layout_height="144dp"
app:theme="#style/ThemeOverlay.AppCompat.Dark.ActionBar">
<android.support.design.widget.CollapsingToolbarLayout
android:id="#+id/collapsing_toolbar_goal_detail"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="#dimen/content_space_double"
app:collapsedTitleTextAppearance="#style/title.dark"
app:expandedTitleTextAppearance="#style/display3.plus.dark"
app:layout_scrollFlags="scroll|exitUntilCollapsed">
<android.support.v7.widget.Toolbar
android:id="#+id/toolbar_goal_detail"
style="#style/toolbar"
app:layout_collapseMode="pin"
app:popupTheme="#style/ThemeOverlay.AppCompat.Light"/>
</android.support.design.widget.CollapsingToolbarLayout>
</android.support.design.widget.AppBarLayout>
<android.support.v4.widget.NestedScrollView
android:id="#+id/nsv_goal_detail"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="#dimen/content_space_half"
android:paddingLeft="#dimen/content_space_half"
android:paddingRight="#dimen/content_space_half"
app:layout_behavior="#string/appbar_scrolling_view_behavior">
<FrameLayout
android:id="#+id/container_goal_detail"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_gravity="fill_vertical"/>
</android.support.v4.widget.NestedScrollView>
</android.support.design.widget.CoordinatorLayout>
Any ideas would be appreciated!

OK! After a solid DAY of debugging every single component of my layout and Fragment I identified what I believe is a bug.
First, the issue: Turns out that having elements in your NSV's child view that change visibility to View.GONE upon runtime are causing the list to scroll down. I noticed that the list scrolls to just above the element where the visibility was toggled (including any margins set on the view).
Second, the fix: I fixed this issue by setting all the views to have android:visibility="gone" in the xml layout, then, I toggle each view's visibility as needed. Previously, the views were visible by default and then I worked from there. I just needed to change my logic to start with them all GONE, not terribly difficult.
I assume this works because the views you are going to hide at runtime do not form a part of the overall height calculation when the NSV is created in onCreateView(). Once the fragment progresses past onCreateView() it's safe to dynamically change the views, however, if the views are calculated as part as the height in onCreateView() and THEN hidden with View.GONE, measurements go wonky and you end up with a list scrolled down significantly.

Have you tried adding below line in your viewgroup i.e. FrameLayout in your case
android:descendantFocusability="blocksDescendants"
I think this will also work for you.
If not try it adding in NSV.

In my case, there was an EditText near the bottom of my scrolling content that was grabbing focus. Since NestedScrollView does some weird layout stuff, the focused view didn't scroll to the top when the activity started, so the real cause was not readily apparent. Adding this to the NestedScrollView's child layout fixed it for me:
android:focusableInTouchMode="true"

Your post answer helped me a lot to find out my issue (btw, it was the same). But I got it worked in a different way. I guess you are using a RecyclerView. In my case I'm using 3 RecyclerViews. Well, from your answer I started hiding the recyclers and I found out just one of them was causing this issue. What I did is I populated with a postDelayed:
new Handler().postDelayed(new Runnable() {
#Override
public void run() {
recyler.setLayoutManager(new LinearLayoutManager(getApplicationContext()));
recyler.setAdapter(new MyAdapter(myList));
}
}, 3000);
That worked fine!