Develop Reference

Creating a locked ScrollView in Android

I'm trying to implement a ScrollView in Android that doesn't scroll when adding an item above the current scroll position.
The default implementation of ScrollView behaves as following:
Adding an item above the current scroll position:
Adding an item below the current scroll position:
How can I "lock" the ScrollView prior to adding an item above the current scroll position?
This is my layout file, I've currently overridden both the ScrollView and LinearLayout, but haven't made any alterations yet.
<LinearLayout
android:layout_height="fill_parent"
android:orientation="vertical"
android:layout_width="fill_parent">
<LinearLayout
android:id="#+id/LinearLayout02"
android:layout_height="wrap_content"
android:layout_width="fill_parent"
android:layout_alignParentBottom="true">
<Button
android:id="#+id/Button02"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_weight="1" android:text="Add To Top"
android:onClick="addToStart">
</Button>
<Button
android:id="#+id/Button03"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="Add to End"
android:onClick="addToEnd">
</Button>
</LinearLayout>
<com.poc.scroller.locable.lockablescrollerpoc.LockedScrollView xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:fillViewport="true"
android:scrollbarAlwaysDrawVerticalTrack="true"
android:verticalScrollbarPosition="right"
android:fadeScrollbars="false"
android:background="#color/scrollColor">
<com.poc.scroller.locable.lockablescrollerpoc.LockedLinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical"
android:id="#+id/Container">
</com.poc.scroller.locable.lockablescrollerpoc.LockedLinearLayout>
</com.poc.scroller.locable.lockablescrollerpoc.LockedScrollView>
</LinearLayout>
</android.support.constraint.ConstraintLayout>
Example Source Code:
https://github.com/Amaros90/android-lockable-scroller-poc
Thank you!

You can easily get the opposite behavior by using addOnLayoutChangeListener of your LinearLayout and reset the ScrollView's ScrollY. Here is the implementation in your ScrollViewActivity.onCreate
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.scrollview);
_linearLayout = (LockedLinearLayout)findViewById(R.id.Container);
_scrollView = (LockedScrollView)findViewById(R.id.ScrollView);
_layoutInflater = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);
_linearLayout.addOnLayoutChangeListener(new View.OnLayoutChangeListener() {
#Override
public void onLayoutChange(View v, int left, int top, int right, int bottom, int oldLeft, int oldTop, int oldRight, int oldBottom) {
_scrollView.scrollTo(0, _scrollView.getScrollY() + (bottom - oldBottom ));
}
});
addExampleImage(10, _linearLayout);
}
Then you can easily flag the addToEnd function or check where the child was added to avoid changing scroll when some child is added to the bottom.

You can try to use RecyclerView and implement onDataSetChanged(). Then detect whether add to TOP or add to END button was pressed. Then use scrollToPositionWithOffset(int, int) to manage the scroll.
For example:
//Scroll item 3 to 20 pixels from the top
linearLayoutManager.scrollToPositionWithOffset(3, 20);
For restoring the scroll position of a RecyclerView, this is how to save the scroll positions (the two arguments for the method scrollToPositionWithOffset(int, int)):
int index = linearLayoutManager.findFirstVisibleItemPosition();
View v = linearLayoutManager.getChildAt(0);
int top = (v == null) ? 0 : (v.getTop() - linearLayoutManager.getPaddingTop())

Implementing this worked for me. You can check out the example app I added in the original question.
public class LockableScrollView extends ScrollView {
private boolean _enabled = true;
public LockableScrollView(Context context, AttributeSet attrs) {
super(context, attrs);
super.setFillViewport(true);
}
#Override
public void addView(View layout, ViewGroup.LayoutParams params) {
super.addView(layout, params);
((ViewGroup)layout).setOnHierarchyChangeListener(new OnHierarchyChangeListener() {
#Override
public void onChildViewAdded(View layout, View item) {
if (_enabled) {
item.addOnLayoutChangeListener(new View.OnLayoutChangeListener() {
#Override
public void onLayoutChange(View item, int left, int top, int right, int bottom, int oldLeft, int oldTop, int oldRight, int oldBottom) {
item.removeOnLayoutChangeListener(this);
int scrollViewY = ((LockableScrollView)item.getParent().getParent()).getScrollY();
int layoutPosition = ((View)item.getParent()).getTop();
boolean shouldScroll = item.getTop() + layoutPosition <= scrollViewY || item.getBottom() + getTop() <= scrollViewY;
if (shouldScroll) {
final int childViewHeight = item.getHeight();
((View)item.getParent()).addOnLayoutChangeListener(new View.OnLayoutChangeListener() {
#Override
public void onLayoutChange(View layout, int left, int top, int right, int bottom, int oldLeft, int oldTop, int oldRight, int oldBottom) {
layout.removeOnLayoutChangeListener(this);
LockableScrollView scrollView = ((LockableScrollView)layout.getParent());
scrollView.scrollTo(scrollView.getScrollX(), scrollView.getScrollY() + childViewHeight);
}
});
}
}
});
}
}
#Override
public void onChildViewRemoved(View layout, View item) {
if (_enabled) {
int scrollViewY = ((LockableScrollView)layout.getParent()).getScrollY();
int layoutPosition = layout.getTop();
boolean shouldScroll = item.getTop() + layoutPosition <= scrollViewY || item.getBottom() + getTop() <= scrollViewY;
if (shouldScroll) {
final int childViewHeight = item.getHeight();
layout.addOnLayoutChangeListener(new View.OnLayoutChangeListener() {
#Override
public void onLayoutChange(View layout, int left, int top, int right, int bottom, int oldLeft, int oldTop, int oldRight, int oldBottom) {
layout.removeOnLayoutChangeListener(this);
LockableScrollView scrollView = ((LockableScrollView)layout.getParent());
scrollView.scrollTo(scrollView.getScrollX(), scrollView.getScrollY() - childViewHeight);
}
});
}
}
}
});
}
}

you can do it easily just get it..
first of all in onclick event store the int value by
using getFirstVisiblePosition()
example.
in onclick of add element button do this---
int currentpos = recycleview.getFirstVisiblePosition();
now after you insert elment to list/recyclerview---
recyclerview.scrolltoposition(currentpos);
thats it try if you want to do it without error..
Good Luck :)

Animate newly created View of unknown size

I want to animate View right after it was added to parent (something like DrawerLayout). The problem is that View has varying size, and animation target position depends on that size. Simplified sample code:
AnimatingView extends View {
public int offsetX;
#Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
final int screenWidth = MeasureSpec.getSize(widthMeasureSpec);
final int screenHeight = MeasureSpec.getSize(heightMeasureSpec);
offsetX = calculateOffset(screenWidth);
...
}
}
Code similar to this triggers the animation:
#Override
public void onClick(View v) {
AnimatingView animatingView = new AnimatingView(getContext());
parentLayout.addView(animatingView);
animatingView.animate().x(animatingView.offsetX).setDuration(500).start();
}
In this case onMeasure() happens after animate(), so animation fails. What is the correct way of doing stuff which depends on view measuring?
The simple & stupid way would be something like animateOnceAfterMeasuring() based on isInitialized flag, but I don't think it the correct way of doing this.

this should work:
AnimatingView animatingView = new AnimatingView(getContext());
parentLayout.addOnLayoutChangeListener(new View.OnLayoutChangeListener() {
#Override
public void onLayoutChange(View v, int left, int top, int right, int bottom, int oldLeft, int oldTop, int oldRight, int oldBottom) {
v.removeOnLayoutChangeListener(this);
animatingView.animate().x(animatingView.offsetX).setDuration(500).start();
}
});

You can use the ViewTreeObserver for this
#Override
public void onClick(View v) {
final AnimatingView animatingView = new AnimatingView(getContext());
parentLayout.addView(animatingView);
animatingView.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
#Override
public void onGlobalLayout() {
if (Build.VERSION.SDK_INT < 16) {
animatingView.getViewTreeObserver().removeGlobalOnLayoutL‌​istener(this);
} else {
animatingView.getViewTreeObserver().removeOnGlobalLayoutList‌​ener(this);
}
animatingView.animate().x(animatingView.offsetX).setDuration(500).start();
}
});
}

RecyclerView itemView OnGlobalLayoutListener doesn't fire for all itemViews

I have a RecyclerView in whose view holder constructor I'm adding an onGlobalLayoutListener as follows
public CustomViewHolder(final View itemView, Context context) {
super(itemView, context);
itemView.getViewTreeObserver().addOnGlobalLayoutListener(
new ViewTreeObserver.OnGlobalLayoutListener() {
#Override
public void onGlobalLayout() {
// Get height here
}
});
}
This fires for all itemViews that are visible on the screen, but as I scroll the recyclerView, it doesn't fire for the itemViews that start to appear on the screen. Why is that? How can I capture this listener for those items?

Register an OnLayoutChangeListener like this:
imageViewAvatar.addOnLayoutChangeListener(new View.OnLayoutChangeListener() {
#Override
public void onLayoutChange(View v, int left, int top, int right, int bottom, int oldLeft, int oldTop, int oldRight, int oldBottom) {
imageViewAvatar.removeOnLayoutChangeListener(this);
// Get height here
}
});

You can use OnPreDrawListener instead of OnGlobalLayoutListener on ViewTreeObserver
public CustomViewHolder(final View itemView, Context context) {
super(itemView, context);
ViewTreeObserver vto = getViewTreeObserver();
vto.addOnPreDrawListener(
new ViewTreeObserver.OnPreDrawListener() {
#Override
public boolean onPreDraw() {
vto.removeOnPreDrawListener(this);
// Get height here
return true;
}
});
}
Or in Kotlin:
val vto = viewTreeObserver
vto.addOnPreDrawListener(
object: ViewTreeObserver.OnPreDrawListener {
override fun onPreDraw(): Boolean {
viewTreeObserver.removeOnPreDrawListener(this)
//Your code
return true
}
}
)

How do i know, when view is drawn?

My Activity layout has View, i have get Y position this view at the beginning of the program, but if i shall insert in bottom method onCreate , i get position value = 0. How i can know, when view is drawn and get her Y position. I try get Y position when i click on button, position get good, but i have get position without using the button.
I get position:
private float cardsStartPosition = 0;
if (cardsStartPosition == 0) {
cardsStartPosition = commonCardContainer.getY();
}
Thanks for answer.

Try this method..It works fine for me.
ViewTreeObserver vto = YourView.getViewTreeObserver();
vto.addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
#Override
public void onGlobalLayout() {
//do your stuff here
}
});

Add a global layout listener to your view, you will get notified when layout is done and your view has dimensions ...
view.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
#Override
public void onGlobalLayout() {
//Here you can get your dimensions
int width = view.getWidth();
//View.removeOnGlobalLayoutListener(this);
}
});

You mention just View. So if that means it's your custom view, you can override the onLayout():
#Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
...;
}
This way you can observe any layout changes of your view. If you're also interested in size changes, there's also the onSizeChanged():
#Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
...;
}
If it's not your custom view, I'd go with the Ketan Ahir's way.

android- How to get the width and height of the list view dynamically

In my application i want display list view using adapter. But i want get the current height and width of the list view (means after generating the list using adapter). how to get it. can anybody help me.
thanks

Use getWidth() and getHeight() method of ListView in onWindowFocusChanged to get the width and height.
#Override
public void onWindowFocusChanged(boolean hasFocus) {
super.onWindowFocusChanged(hasFocus);
System.out.println("Width:" + listview.getWidth());
System.out.println("Height:" + listview.getHeight());
}

To get current width or height of any view, you need to set onLayoutChange listener
public class MainActivity extends Activity implements OnLayoutChangeListener {
private View newView;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
newView = getLayoutInflater().inflate(R.layout.main_activity, null);
newView.addOnLayoutChangeListener(this);
setContentView(newView);
}
public void onLayoutChange(View v, int left, int top, int right,
int bottom, int oldLeft, int oldTop, int oldRight, int oldBottom) {
//Here you can get size of you ListView, e.g:
mylistView.getWidth();
}
#Override
protected void onDestroy() {
super.onDestroy();
newView.removeOnLayoutChangeListener(this);
}
}
27Nov15 - This is a good answer, I think you should release the resource too though. This might not matter so much for an Activity, but the same approach can be used by fragments where they may come and go more frequently.