android - Roid SurfaceView Canvas clear bitmap -

after emptying bitmap, redrawn, , displays.not empty

//draw bitmap private void drawpattern(int x, int y) {     canvas canvas = mholder.lockcanvas();     canvas newcanvas = new canvas(mdrawbitmap);     mcanvases.add(newcanvas);     newcanvas.drawbitmap(mbitmap, x, y, mpaint);     newcanvas.drawcolor(color.black);     canvas.drawbitmap(mdrawbitmap, x, y, mpaint);     mholder.unlockcanvasandpost(canvas); }  //empty, public void setboardbackgroundcolor() {     canvas canvas = mholder.lockcanvas(null);     paint paint = new paint();     paint.setxfermode(new porterduffxfermode(porterduff.mode.clear));     canvas.drawpaint(paint);     paint.setxfermode(new porterduffxfermode(porterduff.mode.src));     mholder.unlockcanvasandpost(canvas);  } 

1.drawpattern 2.setboardbackgroundcolor 3.drawpattern
before painting come out again