Android Canvas is null

Question

Can these two expressions both be true at one time? holder.getSurface().isValid() == true; and canvas = holder.lockCanvas() canvas == null;

ALiGOTec · Accepted Answer · 2012-09-26 07:09:56Z

1

From references:

isValid() - Does this object hold a valid surface? Returns true if it holds a physical surface, so lockCanvas() will succeed.

So, if lockCanvas() succeeds it returns a non null canvas.

But you shouldn't access Surface directly (you need synchronization), in surfaceChanged you can just call canvas = holder.lockCanvas() and draw only if canvas is not null.

edited Sep 26, 2012 at 7:09

answered Sep 26, 2012 at 7:02

ALiGOTec

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2 Comments

Victoria Seniuk Over a year ago

Is it meen that I need to implement SurfaceHolder.Callback and check drawing possibility in surfaceCreated method?

ALiGOTec Over a year ago

the SurfaceHolder is initialized asynchronous so, basicaly if you want to draw on it you should have a SurfaceHolder.Callback (to know when it is ready), and the best place to do the drawings is in surfaceChanged (which is called after surfaceCreated) and where you are provided with width, height and holder.

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