How can I get the bitmap of the canvas I get in onDraw?

Question

How can I create the bitmap from the canvas of custom view.

@user940016 - your question shows no research, or any attempt to solve the problem yourself. read this for more information: http://stackoverflow.com/questions/how-to-ask — katzenhut, May 22 '14 at 10:38

score 37 · Answer 1 · answered Jun 03 '13 at 13:11

37

While there is no getBitmap() function for a canvas, since you are making a custom view, what you can do instead is write a function like this inside your view class.

public Bitmap get(){
   return this.getDrawingCache();
}

This returns the Bitmap of the view, but it is important that in all your constructors you add this,

this.setDrawingCacheEnabled(true);

Otherwise getDrawingCache will return null

answered Jun 03 '13 at 13:11

jcw

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it will give always null object? – srinivas Jan 20 '14 at 06:57
@sri - did you add `setDrawingCacheEnabled(true)` to the constructors of your view? – jcw Jan 20 '14 at 17:15
i have try you code but geting null.Any other solution? – Ravi Bhandari Dec 10 '14 at 09:47
3

Lifesaver! Thanks a lot. Couldn't find this anywhere. – Olaia Dec 30 '14 at 19:12
4

looks like `getDrawingCache` is being deprecated: https://developer.android.com/reference/android/view/View#getDrawingCache() – TinyTimZamboni Apr 23 '19 at 22:05

kostja · Accepted Answer · 2015-08-23T07:43:51.127

15

There is no way to extract the Bitmap out of a Canvas. The only way you can access it is to pass it yourself when creating the canvas like this new Canvas(myBitmap) and keep the reference.

EDIT2: see @Alex comment blow - the approach of passing a Bitmap to the Canvas does not seem to work for more recent versions of Android.

EDIT : If you don't create the Canvas yourself, you could create a screen-sized Bitmap (or whatever size you need) and then pass it to the Canvas in onDraw calls like this: canvas.setBitmap(myBitmap).

edited Aug 23 '15 at 07:43

answered Jun 01 '12 at 09:31

kostja

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But if I use onDraw, I get a canvas rather than creating it myself, so I don't have a reference to the bitmap... – user940016 Jun 01 '12 at 10:00
2

If you don't create the `Canvas` yourself, you can not interact with its `Bitmap`. Calling `canvas.setBitmap()` in `onDraw()` causes `UnsupportedOperationException` – Alex Aug 21 '15 at 09:35
this may have changed in the last 3 years. The last time I tried was with 2.3 :) What is the version you have tried it with? And thanks for noticing, I will edit accordingly. – kostja Aug 23 '15 at 07:43
This approach won't work with a hardware accelerated canvas. – Johann May 04 '21 at 17:03

score 2 · Answer 3 · answered Jan 10 '20 at 10:40

getDrawingCache() is deprecated in API 28.

So now you may use following code inside your custom view

Bitmap bitmap = Bitmap.createBitmap(getWidth(), getHeight(), Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);
draw(canvas);
// return bitmap; -- this is the bitmap you need

If you want to use this code outside your cusom view use methods like viewInstance.getHeight()... viewInstance.draw(canvas) will draw the view on the bitmap

score 1 · Answer 4 · answered Jun 01 '12 at 10:02

1

I found out that Canvas has a setBitmap function, but not a getBitmap one. It's strange, but anyway, it enables me to create the bitmap myself and pass it to the canvas, retaining the reference.

answered Jun 01 '12 at 10:02

user940016

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How can I get the bitmap of the canvas I get in onDraw?

4 Answers4

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