RecyclerView LayoutManager findViewByPosition returns null
I'm interested in what is the right and first possible moment to get size of first item of RecyclerView?
I've tried to use:
recyclerView.setLayoutManager(new GridLayoutManager(context, 2));
recyclerView.setAdapter(new MyDymmyGridRecyclerAdapter(context));
recyclerView.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
@Override
public void onGlobalLayout() {
recyclerView.getViewTreeObserver().removeGlobalOnLayoutListener(this);
View firstRecyclerViewItem = recyclerView.getLayoutManager().findViewByPosition(0);
// firstRecyclerViewItem is null here
}
});
but it returns null at this moment.
If you're using OnGlobalLayoutListener you should remember onGlobalLayout can be called multiple times. Some of those calls can happen even before Layout is ready (and by ready I mean the moment when you can get dimensions of a View by calling view.getHeight() or view.getWidth() ). So the proper way of implementing your approach would be:
recyclerView.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
@Override
public void onGlobalLayout() {
int width = recyclerView.getWidth();
int height = recyclerView.getHeight();
if (width > 0 && height > 0) {
if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.JELLY_BEAN) {
recyclerView.getViewTreeObserver().removeOnGlobalLayoutListener(this);
} else {
recyclerView.getViewTreeObserver().removeGlobalOnLayoutListener(this);
}
}
View firstRecyclerViewItem = recyclerView.getLayoutManager().findViewByPosition(0);
}
});
Apart from that you still need to be sure that at the time of findViewByPosition(0) call:
RecyclerView's Adapter has at least one data element. View at position 0 is currently visible in RecyclerView Tell me if that fixes your issue, if not there is still another way of doing what you need.
在我的扩展RecyclerView像这样覆盖onChildAttachedToWindow
@Override
public void onChildAttachedToWindow(View child) {
super.onChildAttachedToWindow(child);
if (!mIsChildHeightSet) {
// only need height of one child as they are all the same height
child.measure(0, 0);
// do stuff with child.getMeasuredHeight()
mIsChildHeightSet = true;
}
}
I had this type of problem. I want to perform click by default on the first visible position of the recylerview. I wrote the code for that on onResume but it did not work. I solved my problem by writting the code in onWindowFocusChanged method
@Override
public void onWindowFocusChanged(boolean hasFocus) {
super.onWindowFocusChanged(hasFocus);
if(isCalledForTheFirstTime)
{
LinearLayoutManager manager= (LinearLayoutManager) rcViewHeader.getLayoutManager();
int pos= manager.findFirstCompletelyVisibleItemPosition();
View view=manager.findViewByPosition(pos);
if(view!=null)
{
view.performClick();
}
// change the vaule so that it would not be call in case a pop up appear or disappear
isCalledForTheFirstTime=false;
}
}