When does Android take its recent apps switcher screenshot?

Question

I am developing an app that has private information and should not display a real screenshot in Android's recent app switcher. I've tried a variation of this solution, by setting the content view to an ImageView inside the onPause function, but it seems that the operating system takes a screenshot before the content view is changed to the custom image.

I am also aware of setting the window's layout parameter flags to secure, making the screenshot completely white, but I'd hope that there would be a way to customize the screenshot.

So, I'm wondering at what point that Android takes a screenshot of the app for the app switcher (specifically in KitKat and Lollipop).

Answer 1

EDIT

It is no longer possible to customize the screenshot which system uses to present the thumbnail in the recent apps.

Old answer

Take a look at method Activity.onCreateThumbnail - this is exactly what you're looking for as it let you draw your own thumbnail for Recent screen.

You get Canvas as one of the parameters in which you can draw (or not draw at all) directly. The main point is that you have to return true from this method, which indicates that system won't draw thumbnail itself.

The simpliest solution would be:

@Override
public boolean onCreateThumbnail (Bitmap outBitmap, Canvas canvas) {
    // Do nothing or draw on Canvas
    return true;
}

or if you want to draw your own Bitmap

@Override
public boolean onCreateThumbnail (Bitmap outBitmap, Canvas canvas) {
    Bitmap myBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.myBitmap);
    canvas.drawBitmap(myBitmap, 0, 0, null);

    return true;
}