Question

So I have an animation that is being created by having a bunch of bitmaps drawn in the onDraw() method of a custom view. There is an update thread that calls a method in the custom view that changes the positions of the bitmaps to be drawn by the onDraw() method. What I would like to do is to save the bitmap created each time the update thread is finished so that i can create a gif from the bitmaps that i save.

I found the below code to save a png from a bitmap stored in memory to the SD card and that works with a stored bitmap but I’m having trouble with getDrawingCache():

public void saveView(){
    if(counter < 200){
        try {
            counter++;
            System.out.println("Counter : " + counter);
            File file = new File(path, "star"+counter+".png");
            file.delete();
            OutputStream fOut = new FileOutputStream(file);
            buildDrawingCache();
            getDrawingCache().compress(Bitmap.CompressFormat.PNG, 100, fOut);
            destroyDrawingCache();
            fOut.flush();
            fOut.close();
            MediaStore.Images.Media.insertImage(context.getContentResolver(),file.getAbsolutePath(),file.getName(),file.getName());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Doing this essentially does two things right now:

1) It takes about 50 images and saves them to the sd card. @ around 50 it causes the heap to get to large (i guess destroyDrawingCache() is unable to actually finish due to this is in a seperate thread)

2) In the pictures taken, you can see the scan lines from the buffer updating because I’m taking from a buffer that gets updated.

It would seem the getDrawingCache calls onDraw() as well which is why I can’t have this on the UI thread in the onDraw itself.

If this is possible please help.

Answer 1

You should not call getDrawingCache() from outside the UI thread. That’s why the bitmaps you get have partially updated scan lines. Call saveView() directly from onDraw(). Only the file operations may be run on separate threads after making a clone of the cached bitmap.

Note: You can call setDrawingCacheEnabled(true)? so that you don’t have to call buildDrawingCache() and destroyDrawingCache(). Also if your device has hardware acceleration is turned on, you’ll have to call setLayerType(LAYER_TYPE_SOFTWARE, null).

Another solution is to get the bitmap by calling View.draw(android.graphics.Canvas) on a new canvas that holds a blank bitmap.