Android setBitmap to canvas

Question

i want to convert canvas to image and save it on device. But when I set bitmap to canvas I get error java.lang.UnsupportedOperationException. My full code:

public class SingleTouchEventView extends View {
private Paint paint = new Paint();
private Path path = new Path();


public SingleTouchEventView(Context context, AttributeSet attrs) {
    super(context, attrs);

    paint.setAntiAlias(true);
    paint.setStrokeWidth(6f);
    paint.setColor(Color.WHITE);
    paint.setStyle(Paint.Style.STROKE);
    paint.setStrokeJoin(Paint.Join.BEVEL);
}

@Override
protected void onDraw(Canvas canvas) {
    canvas.drawPath(path, paint);
    canvas.drawCircle(50, 50, 3, paint);
    Bitmap bitmap = Bitmap.createBitmap(canvas.getWidth(), canvas.getHeight(), Bitmap.Config.ARGB_8888);
    canvas.setBitmap(bitmap);
    try {

        File file = new File(Environment.getExternalStorageDirectory() + "/image.jpg");
        bitmap.compress(Bitmap.CompressFormat.JPEG, 100, new FileOutputStream(file));
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

}

Maybe someone could help me to solve this problem?

Answer 1

That isn't how you draw to a bitmap. You do NOT use the canvas that draws to the screen. You create a second canvas, passing in the bitmap you want to draw to as a parameter in the constructor. Then any draw commands to that canvas will draw the bitmap. Then you draw that bitmap to the screen. Something like this:

Canvas myCanvas = new Canvas(myBitmap);
myCanvas.drawLine();
myCanvas.drawCircle();
//Insert all the rest of the drawing commands here
screenCanvas.drawBitmap(myBitmap, 0, 0);

I also would not write it to the file system in onDraw - I'd expect drawing performance to suffer badly if you do. A separate function call can do that. If you keep myBitmap around in a variable, you can just compress it anytime to write out the last draw to disk.