Why do we use
ViewTreeObserver
, please can anyone explain it?In below code
creditsView
isTextView
object. By this whole code I understand that “this is to hide some text based on condition”, but only thing is why we are usingViewTreeObserver
?mainLayout.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() { @Override public void onGlobalLayout() { int heightDiff = mainLayout.getRootView().getHeight() - mainLayout.getHeight(); if (heightDiff > 100) { Utils.appLogger("MyActivity", "keyboard opened"); creditsView.setVisibility(View.GONE); } if (heightDiff < 100) { Utils.appLogger("MyActivity", "keyboard closed"); creditsView.setVisibility(View.VISIBLE); } } });
Answer
If you hadn’t used ViewTreeObserver
, than mainLayout.getRootView().getHeight()
would simply return 0px, because it hasn’t been laid out yet (see getWidth()
and getHeight()
of View
returns 0).
Thus, you are waiting until view is measured, laid out, and then you are fetching width/height values from it. This callback will be fired exactly when the view is going to be laid out on the screen.
Attribution
Source : Link , Question Author : Prasanth Yejje , Answer Author : azizbekian