ViewGroupOverlay doesn't show view

问题

I'm currently trying to create a puzzle game where I have a grid and each cell should be able to show a visual (and only visual) indication on touch. Therefore, I intent to use the ViewGroupOverlay (with getOverlay()) with a custom view:

In each CellView

 @Override
    public boolean onTouchEvent(MotionEvent event) {
        if(event.getAction() == MotionEvent.ACTION_DOWN) {
            LayoutInflater inflater = (LayoutInflater) getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            View myView = inflater.inflate(R.layout.overlay, null);
            gridView.getOverlay().add(myView);
        }
        if(event.getAction() == MotionEvent.ACTION_UP || event.getAction() == MotionEvent.ACTION_CANCEL) {
            gridView.getOverlay().clear();
        }
        return super.onTouchEvent(event);
    }

where 'gridView' is the parent (a FrameLayout containing a GridLayout that holds the multiple CellViews (which are RelativeLayout)) ;). But I think that doesn't really matters...

And currently for the overview.xml (Just dummy code)

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#dddd090d">

        <TextView
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:textAppearance="?android:attr/textAppearanceLarge"
            android:text="Test" />

</LinearLayout>

Sadly, the overlay view doesn't appear anywhere.

However, if I try it with a drawable and the following code in 'onTouchEvent', it works... But I would need the view and not the drawable to work...

Drawable myIcon = getResources().getDrawable(R.drawable.overlay);
myIcon.setBounds(0,0,100,100);
gridView.getOverlay().add(myIcon);

In general, the Overlay-technique added in API18 seems to be never used. Any experts here?

回答1:

ViewGroupOverlay doesn't perform the layout pass on Views added to it; that is, as is automatically performed when adding a View to an existing layout, you need to manually perform measure() and layout() on a view in order for it to be correctly displayed on screen.

The reason your code works with the Drawable is because you are performing the layout step with myIcon.setBounds(0,0,100,100);

If you use this code you will get the same effect as your Drawable:

    View view = inflater.inflate(R.layout.overlay, null);
    view.measure(View.MeasureSpec.makeMeasureSpec(100, View.MeasureSpec.EXACTLY), View.MeasureSpec.makeMeasureSpec(100, View.MeasureSpec.EXACTLY));
    view.layout(0, 0, 100, 100);
    gridView.getOverlay().add(view);

You can read more about measure/layout here: https://developer.android.com/guide/topics/ui/how-android-draws.html

You can use this helper method to display a view as if it has been added to an empty full screen:

private static void measureAndLayout(Activity activity, View toMeasure, int statusBarHeight) {
    DisplayMetrics displayMetrics = new DisplayMetrics();
    activity.getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);

    toMeasure.measure(
            View.MeasureSpec.makeMeasureSpec(displayMetrics.widthPixels, View.MeasureSpec.EXACTLY) ,
            View.MeasureSpec.makeMeasureSpec(displayMetrics.heightPixels - statusBarHeight, View.MeasureSpec.EXACTLY));

    toMeasure.layout(0, statusBarHeight, displayMetrics.widthPixels, displayMetrics.heightPixels);
}

回答2:

You need to set setBottom, setRight, to your View you want to add to ViewGroupOverlay

Just like I wrote here http://uiandroid.com/reveal-effect-custom-color/

来源：https://stackoverflow.com/questions/31862961/viewgroupoverlay-doesnt-show-view