cannot seem to get bitmap from view in android

Question

My problem is similar to the one in Android View.getDrawingCache returns null, only null.

My code used to work with the method

private Bitmap getBitmapFromView(View v) {
    v.setDrawingCacheEnabled(true);
    v.measure(MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED),
        MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED));
    v.layout(0, 0, v.getMeasuredWidth(), v.getMeasuredHeight());
    v.buildDrawingCache(true);
    Bitmap b = Bitmap.createBitmap(v.getDrawingCache());
    v.setDrawingCacheEnabled(false); // clear drawing cache
    return b;
}

But today I changed the xml layout file. Since the change I have been getting NullPointerException at the line Bitmap b = Bitmap.createBitmap(v.getDrawingCache()). So I tried changing the method getBitmapFromView to

public static Bitmap loadBitmapFromView(View v) {
    Bitmap b = Bitmap.createBitmap(v.getLayoutParams().width, v.getLayoutParams().height, Bitmap.Config.ARGB_8888);
    Canvas c = new Canvas(b);
    v.layout(0, 0, v.getLayoutParams().width, v.getLayoutParams().height);
    v.draw(c);
    return b;
}

But that didn't help. I get the null in the very first line.

The situation is this: I am trying to convert the view into a bitmap. But I am doing this without first displaying the view on screen. Again, this all used to work until I changed the content of the xml layout file. The change was not even that big. I just moved stuff around and removed -- yes removed -- some of the subviews.

In any case, I know for certain there is no problem with my layout file because I can display it on screen if I want; which I have done as part of troubleshooting.

Someone suggested using a handler to call getDrawingCache(). If that's the answer, how would I write that code?

UPDATE

View view = activity.getLayoutInflater().inflate(R.layout.my_view, null, false);
    findViewsByIds(view);//where I inflate subviews and add content to them.

Answer 1

Since you are not showing the view it's easier to just draw the view on a canvas. You are already trying to do that but I would merge both methods into one without using drawing cache.

private Bitmap getBitmapFromView(View v) {
    v.measure(MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED),
            MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED));
    v.layout(0, 0, v.getMeasuredWidth(), v.getMeasuredWidth());
    Bitmap b = Bitmap.createBitmap(v.getMeasuredWidth(), v.getMeasuredWidth(), Bitmap.Config.ARGB_8888);
    Canvas c = new Canvas(b);
    v.draw(c);
    return b;
}

Also check that MeasureSpec.UNSPECIFIED may not work well without the view in layout so you may need to specify a width and height.

Answer 2

Execute createBitmapFromView when the view is measured.

public static void executeWhenViewMeasured(final View view, final Runnable runnable) {
    if(view.getMeasuredHeight() == 0 || view.getMeasuredWidth() == 0){
        view.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
            @Override
            public void onGlobalLayout() {
                runnable.run();
                removeGlobalOnLayoutListener(view, this);
            }
        });
    } else {
        runnable.run();
    }
}

public static Bitmap createBitmapFromView(View view) {
    Bitmap bitmap = Bitmap.createBitmap(view.getMeasuredWidth(), view.getMeasuredHeight(), Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(bitmap);
    view.draw(canvas);
    return bitmap;
}

@TargetApi(Build.VERSION_CODES.JELLY_BEAN)
public static void removeGlobalOnLayoutListener(View view,
                                                ViewTreeObserver.OnGlobalLayoutListener listener) {
    try {
        view.getViewTreeObserver().removeOnGlobalLayoutListener(listener);
    } catch (NoSuchMethodError e) {
        view.getViewTreeObserver().removeGlobalOnLayoutListener(listener);
    }
}

executeWhenViewMeasured(view, new Runnable() {
            @Override
            public void run() {
                Bitmap bitmap = createBitmapFromView(view);
            }
        });