android - setting up drawable.invalidate to continuously draw on canvas -

i trying incrementally change alpha value of ovalshape().. need call invalidate , keeps calling , render increased alpha value..

but setup wrong, dont have idea this..

public class xml_anim_testing_sub_class extends view {     private shapedrawable mdrawable;     int x = 10;     int y = 10;     int width = 300;     int height = 50;     int my_alpha = 255,add_to_my_alpha = 0;      public xml_anim_testing_sub_class(context context) {         super(context);     }      protected void ondraw(canvas canvas) {         x++;         mdrawable = new shapedrawable(new ovalshape());         mdrawable.getpaint().setcolor(0xff74ac23);         mdrawable.setalpha(my_alpha += add_to_my_alpha );         mdrawable.setbounds(x, y, x + width, y + height);         if (my_alpha == 0)             add_to_my_alpha  = 1;         if (my_alpha == 255)             add_to_my_alpha  = -1;         mdrawable.draw(canvas);         mdrawable.invalidateself();     } } 

ok, found out solution, invalidate(), difference between invalidate , postinvalidate? cos both working..

also, use of?

mdrawable.invalidateself()(cb); 

instead of calling mdrawable.invalidateself(), call postinvalidate() (for view itself). schedule drawing pass after current 1 finishes.

also, don't need allocate new shapedrawable each time through ondraw. assign in constructor once. cut down on garbage generation.