Question

This question has been asked several times in various forms but I haven’t found a definitive answer.

I need to be able to get dimensions and positions of descendant Views after the initial layout of a container (a contentView). The dimensions required in this case are of a View(Group) that is not predictable – might have multiple lines of text, minimum height to accommodate decoration, etc. I don’t want to do it every on every layout pass (onLayout). The measurement I need is a from a deeply nested child, so overriding the onLayout/onMeasure of each container in between seems a poor choice. I’m not going to do anything that’ll cause a loop (trigger-event-during-event).

Romain Guy hinted once that we could just .post a Runnable in the constructor of a View (which AFAIK would be in the UI thread). This seems to work on most devices (on 3 of the 4 I have personally), but fails on Nexus S. Looks like Nexus S doesn’t have dimensions for everything until it’s done one pass per child, and does not have the correct dimensions when the posted Runnable‘s run method is invoked. I tried counting layout passes (in onLayout) and comparing to getChildCount, which again works on 3 out of 4, but a different 3 (fails on Droid Razr, which seems to do just one pass – and get all measurements – regardless of the number of children). I tried various permutations of the above (posting normally; posting to a Handler; casting getContext() to an Activity and calling runOnUiThread… same results for all).

I ended up using a horrible shameful no-good hack, by checking the height of the target group against its parent’s height – if it’s different, it means it’s been laid out. Obviously, not the best approach – but the only one that seems to work reliably between various devices and implementations. I know there’s no built-in event or callback we can use, but is there a better way?

TYIA

/EDIT The bottom line for me I guess is that the Nexus S does not wait until after layout has completed when .posting() a Runnable, as is the case on all other devices I’ve tested, and as suggested by Romain Guy and others. I have not found a good workaround. Is there one?

Answer 1

I’ve been successful using the OnGlobalLayoutListener.

It worked great on my Nexus S

final LinearLayout marker = (LinearLayout) findViewById(R.id.distance_marker);
OnGlobalLayoutListener listener = new OnGlobalLayoutListener() {
    @Override
    public void onGlobalLayout() {
        //some code using marker.getHeight(), etc.
        markersContainer.getViewTreeObserver().removeGlobalOnLayoutListener(this);
    }
};
marker.getViewTreeObserver().addOnGlobalLayoutListener(listener);