CODEWITHSUNDEEP
androidandroid-layoutandroid-activity
Chayy
Chayy

Reputation: 834

How to know when an activity finishes a layout pass?

I have a background thread that updates the UI of my activity, after the onCreate(). It can be adding layouts, or changing the size of others.

I simply want to detect when the layout pass is finished in my activity, to be able to manually update the positions of others views that directly depend on the layouts that were just adde or modified.

For now, I just use a Handler with a postDelayed runnable that does the job, after a small delay, around 50-100 ms after the modifs that triggers the requestLayout().

It works, but we can obviously see the delay. I would like to do the job as soon as possible. In a view code it's simple to detect the measurement pass, but I don't find how to solve this directly in the activity.

Upvotes: 27

Views: 16677

Answers (3)

aaronvargas
aaronvargas

Reputation: 14152

You can use the ViewTreeObserver.OnPreDrawListener

per the docs at https://developer.android.com/reference/android/view/ViewTreeObserver.OnPreDrawListener

At this point, all views in the tree have been measured and given a frame.

Only if a view in your tree requests another layout pass, will any layout bounds change. You could also use similar technique using the ViewTreeObserver.OnDrawListener to get the callback even later

myView.getViewTreeObserver().addOnPreDrawListener(
    new ViewTreeObserver.OnPreDrawListener() {
        @Override
        public boolean onPreDraw() {
            myView.getViewTreeObserver().removeOnPreDrawListener(this);
            // view is measured and laid out
        });

Upvotes: 1

Phillip Fitzsimmons
Phillip Fitzsimmons

Reputation: 2945

A GlobalLayoutListener will fire an event on completion of a layout. Would that suit your needs?

View myView=findViewById(R.id.myView);
  myView.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
            @Override
            public void onGlobalLayout() {
                //At this point the layout is complete and the 
                //dimensions of myView and any child views are known.
            }
        });

Upvotes: 50

Gianluca P.
Gianluca P.

Reputation: 1551

in addition to Phillip Fitzsimmons accepted answer, which is correct, I would also note that if someone needs to know the size in the view itself, the method:

protected void onSizeChanged(int w, int h, int oldw, int oldh) {
  super.onSizeChanged(w, h, oldw, oldh);
  // your code here
}

can be overridden and it will be called after the layout pass.

Upvotes: 2

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