ios - Transition with alpha mask -

i'd create transition between 2 view controllers method:

-(void)animate {      uiimage *maskingimage = [uiimage imagenamed:@"mask.png"];     calayer *masklayer =[calayer layer];     masklayer.anchorpoint=cgpointmake(0.5, 0.5);     masklayer.frame=self.view.superview.frame;     masklayer.contents=(id)self.maskingimage.cgimage;     self.view.layer.mask=masklayer;      cabasicanimation* anim = [cabasicanimation animationwithkeypath:@"transform.scale"];     anim.duration = 2.5;     anim.tovalue=[nsnumber numberwithint:self.view.bounds.size.height/8];     anim.fillmode=kcafillmodeboth;     anim.removedoncompletion=no;     anim.delegate = self;     [self.view.layer.mask addanimation:anim forkey:nil]; } 

where mistake? i've tried other transition , it's works:

-(void)animate {      cabasicanimation* anim = [cabasicanimation animationwithkeypath:@"transform.scale"];     anim.tovalue = [nsnumber numberwithdouble:0.9];     anim.duration = 0.5;     anim.delegate = self;     [self.view.layer addanimation:anim forkey:nil]; } 

mask.png black rectangle centered white circle