Drawable vs Single reusable Bitmap better with mem

问题:

As I understand it (not that I'm correct) Drawables are generally correctly removed from memory when the application is finished with them. Bitmaps however need to be manually recycled, and sometimes even have a special class written to handle them properly. My question is, in regards to memory and leaks, is it more beneficial to simply stick with Drawables like such:

myView.setBackgroundDrawable(getResources().getDrawable(R.drawable.my_image));
myView1.setBackgroundDrawable(getResources().getDrawable(R.drawable.my_image1));
myView2.setBackgroundDrawable(getResources().getDrawable(R.drawable.my_image2));

rather than something like so with Bitmaps:

Bitmap tmpBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.my_image);
myView.setImageBitmap(tmpBitmap);

tmpBitmap.recycle();
tmpBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.my_image1);
myView1.setImageBitmap(tmpBitmap);

tmpBitmap.recycle();
tmpBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.my_image2);
myView2.setImageBitmap(tmpBitmap);
tmpBitmap.recycle();

I've also read of course that you have to be careful about recycle() method on Bitmaps because they can be removed while still in use? It seems like these issues keep popping up in different forms, but I can't really get a straight answer from anyone on the matter. One person says to reuse a Bitmap and recycle after every use, and others say use Drawables and an unbindDrawables() method (this is what I've been using):

private void unbindDrawables(View view) {
    if (view.getBackground() != null) {
        view.getBackground().setCallback(null);
    }
    if (view instanceof ViewGroup) {
        for (int i = 0; i < ((ViewGroup) view).getChildCount(); i++) {
            unbindDrawables(((ViewGroup) view).getChildAt(i));
        }
        ((ViewGroup) view).removeAllViews();
    }
}

Any applicable insight would be much appreciated though. Thanks

回答1:

I back Romain's proposal, but I'm not sure your question is addressing your actual problem. I don't know how you handle the references to your Views. Maybe you simply have memory leaks in your application? A lot of memory leaks in Android are related to Context. When a Drawable is attached to a View, the View is set as a callback on the Drawable.

TextView myView = new TextView(this);
myView.setBackgroundDrawable(getDrawable(R.drawable.my_bitmap));

In the code snippet above, this means the Drawable has a reference to the TextView which itself has a reference to the Activity (the Context) which in turns has references to pretty much anything depending on your code.

Without looking at more of your code I guess you're on the right track by setting the stored drawables' callbacks to null when an Activity is destroyed.

回答2:

Bitmaps do not need to be manually recycled. They are garbage collected just like Drawables and other objects. Similarly you don't need to unbind drawables, except in very specific situations. It seems that you read a lot of misleading information.

Recycling bitmaps and unbinding drawable can be useful in some situations (for instance if your app manipulate large amounts of bitmap data or if you store drawable in a static manner.)

The two examples you show at the beginning of your question are equivalent. If you load a drawable directly, bitmaps will be loaded on your behalf. If you load bitmaps manually and set them on an ImageView, they will be enclosed in drawables on your behalf.

Use the first solution since it's simpler and don't worry about unbinding and other memory management techniques until you actually need them.