Android - Can't draw a bitmap in a canvas -

i have following code works:

protected void ondraw(canvas canvas) {         canvas.drawrect(undobuttonrectf, buttonpaint);     canvas.drawpath(undobuttonarrow, buttonarrowpaint); 

anyway, when exchange following:

protected void ondraw(canvas canvas) {                 undobuttonbitmap = bitmap.createbitmap((int) undobuttonrectf.width(), (int) undobuttonrectf.height(), bitmap.config.argb_8888);          canvas ca = new canvas(undobuttonbitmap);          ca.drawrect(undobuttonrectf, buttonpaint);         ca.drawpath(undobuttonarrow, buttonarrowpaint);          canvas.drawbitmap(undobuttonbitmap, undobuttonrectf.left, undobuttonrectf.top, buttonpaint); 

nothing drawn. how can happen? using bitmap in wrong way? please, me!!!

i suppose there coordinator error.

the error undobuttonrectf contains offsets "canvas", not "ca", should adjust or remove top/left offset before call

 ca.drawrect(undobuttonrectf, buttonpaint);  ca.drawpath(undobuttonarrow, buttonarrowpaint); 

right ?