为什么LinearLayout子getWidth方法返回0？

Question

I have a LinearLayout, and this LinearLayout will hold dynamically placed views. I need to find out what the width of the children of LinearLayout, however this has to be done in onCreate method. From researching I've found out that you can't use getWidth from this method. So instead I'm using onWindowFocusChanged, which works for the parent LinearLayout (returning me the actual size), but it doesn't work with its children.

Another thing I noticed is that when the screen is fading away and the screen is locked, I can see at the logs the actual width of the children being returned (I think the activity is being paused).

I'm really stuck and this is needed because I need to dynamically place those views depending on the children width.

Answer 1

You might be able to get with the below. But as others pointed out, this probably isn't a great idea.

LinearLayout.measure(MeasureSpec.UNSPECIFIED, MeasureSpec.UNSPECIFIED);
LinearLayout.getMeasuredWidth();

Answer 2

inside the onCreate , views still can't know the state of the nearby views and the children ,etc... so only after all is prepared and the layout process is done , you can get the size of views .

here's a quick code for getting the size of the view just before it's being drawn:

private static void runJustBeforeBeingDrawn(final View view, final Runnable runnable)
{
    final ViewTreeObserver vto = view.getViewTreeObserver();
    final OnPreDrawListener preDrawListener = new OnPreDrawListener()
    {
        @Override
        public boolean onPreDraw()
        {
            Log.d(App.APPLICATION_TAG, CLASS_TAG + "onpredraw");
            runnable.run();
            final ViewTreeObserver vto = view.getViewTreeObserver();
            vto.removeOnPreDrawListener(this);
            return true;
        }
    };
    vto.addOnPreDrawListener(preDrawListener);
}

alternatively , you can use addOnGlobalLayoutListener instead of addOnPreDrawListener if you wish.

example of usage :

runJustBeforeBeingDrawn(view,new Runnable()
{
  @Override
  public void run()
  {
    int width=view.getWidth();
    int height=view.getHeight();
  }
});

another approach is to use onWindowFocusChanged (and check that hasFocus==true) , but that's not always the best way ( only use for simple views-creation, not for dynamic creations)

EDIT: Alternative to runJustBeforeBeingDrawn: https://stackoverflow.com/a/28136027/878126

Answer 3

https://stackoverflow.com/a/3594216/1397218

So you should somehow change your logic.