Android - ImageView: setImageBitmap VS setImageDrawable

Question

What is the difference between setImageBitmap and setImageDrawable?

I have an image which I would like to set dynamically from file. The tu

Answer 1

Actually, you may see the difference, if you sometimes use null as an argument:

imageView.setImageDrawable(null);
Drawable d = imageView.getDrawable(); // d == null

imageView.setImageBitmap(null);
Drawable d = imageView.getDrawable(); // d == some BitmapDrawable, != null

so if you are checking for existence of a drawable in ImageView, beware of it.

Answer 2

I just wrote up an article for this. Wish to be able to answer your question.

https://plus.google.com/112740367348600290235/posts/VNAfFLDcKrw

ImageView has 4 APIs to specify the image. Which one to use? What is the difference?

1. setImageDrawable(Drawable drawable)
2. setImageBitmap(Bitmap bm)
3. setImageResource(int resId)
4. setImageURI(URI uri)

ImageView, by the name, is used to display an image. But what is a image? A Bitmap is-a image, not hard to understand and we use setImageBitmap for that purpose. However, internally, the ImageView has-a Drawable but not a Bitmap and that is what setImageDrawable for. When you call setImageBitmap, internally, first the bitmap will be wrapped to BitmapDrawable, which IS-A Drawable, and then call setImageDrawable.

Here is the code.

public void setImageBitmap(Bitmap bm) {
    setImageDrawable(new BitmapDrawable(mContext.getResources(), bm));
}

So, what about the 3 and 4 API?

You should already know that that are bunches of ways to create a bitmap: from a file path, from an input stream, from the Uri, or from the resource file.

BitmapFactory.decodeFile(String pathName)
BitmapFactory.decodeStream(Inputstream)
BitmapFactory.decodeResource(Resource res, int id)
BitmapFactory.decodeByteArray(byte[] data)

Aware of this, it is easy to understand setImageResource/setImageUri is just same as setImageBitmap.

To sum up, setImageDrawable is the primitive function other APIs rely on. The other 3 are just helper methods making you write less code.

In addition, it is very important to keep in mind that ImageView actually has-a Drawable, which not necessarily to be a BitmapDrawable! You could set any Drawable to the Image view.

Besides setting the Drawable through Java API, you could also using XML attribution to set the source Drawable for ImageView. See example below. Note that the shape could be either an image file (.png, .jpg, .bmp) or xml file.

Answer 3

public void setImageBitmap(Bitmap bm) {
// if this is used frequently, may handle bitmaps explicitly
// to reduce the intermediate drawable object
setImageDrawable(new BitmapDrawable(mContext.getResources(), bm));
}

maybe the difference is the mContext.getResources(), from mContext.getResources() can get the density of the divice, so the display on sceen is different

Answer 4

Both methods are valid and achieve the same result. In the first method you wrap your bitmap around a drawable object which is an abstraction for anything that can be drawn in a View.

The special thing about Drawables is that they let you do all kinds of operations on the graphical object they wrap around (scaling, translation, opacity etc..).

A bitmap is one kind of drawable, you can learn further about drawables here: http://developer.android.com/guide/topics/resources/drawable-resource.html

In the second method, you directly access the bitmap bits without any drawable related operations and simply draw the bitmap as-is on your view.

Hope this helps, cheers, Max.

Answer 5

There is no difference between the two internally setImageBitmap is calling setImageDrawable.

Below code is picked from ImageView.java of AOSP

public void setImageBitmap(Bitmap bm) {
    // if this is used frequently, may handle bitmaps explicitly
    // to reduce the intermediate drawable object
    setImageDrawable(new BitmapDrawable(mContext.getResources(), bm));
}