Question

I’m struggling with the problem that the .onWindowFocusChanged() doesn’t get called in my custom Activity class. My setup:

Two tabs (containing Activity_1 and Activity_2) in a TabHost, where the 2nd tab is selected by default:

tabHost.setCurrentTab(currentTabIndex);

In both Activities, I added the onWindowFocusChanged() override (because I need to preform calculations after the layout is done drawing):

@Override
public void onWindowFocusChanged(boolean hasFocus)
{
    super.onWindowFocusChanged(hasFocus);
}

The problem: when the 2nd tab is selected by default, and I click the 1st tab, the onWindowFocusChanged() never gets called within Activity_1 (associated with the 1st tab).
Both Activities extend the normal Activity class.

Any clue on how to fix this would be greatly appreciated!

Answer 1

If you need to wait until a specific View is draw and then make the calculations, you could use viewTreeObserver to listen the layout changes and make your calculations there.
Use it like this:

ViewTreeObserver vto = mainLayout.getViewTreeObserver();
vto.addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
public void onGlobalLayout() {
    // remove the listener so it won't get called again if the view layout changes
    mainLayout.getViewTreeObserver().removeOnGlobalLayoutListener(this);
    // add your calculations here
}}

EDIT:

Credit and thanks to Edison for the further details.

For those who want to support API < 16, you can do

if (Build.VERSION.SDK_INT >= 16) {     
    mainLayout.getViewTreeObserver().removeOnGlobalLayoutListener(this); 
} else { 
    mainLayout.getViewTreeObserver().removeGlobalOnLayoutListener(this); 
}