Android dual-Buffer

Canvas page exchange is indeed a problem for beginners in game development.
After many practices, I found a perfect method:
Use a background canvas bk_canvas, where all updated drawings are carried out. Of course, dirtyrectlist
You only need to maintain one image. You need to first draw the image on bk_canvas, and then copy bk_canvas
How Can I copy the canvas that is displayed?
Bitmap bitmapbase = new Bitmap ()
Canvas bk_canvas = new canvas (bitmapbase)
Bk_canvas.draw ()... // update and draw

Canvas c = lockcanvas (null );
C. drawbitmap (bitmapbase );
Unlock (c )....