Fade in Fade out 淡入淡出效果

-(IBAction)startFade:(id)sender {  
  [_label setAlpha:0.0f]; 
//fade in 
[UIView animateWithDuration:2.0f animations:^{ 
  [_label setAlpha:1.0f]; 
} completion:^(BOOL finished) { 
//fade out [UIView animateWithDuration:2.0f animations:^{ 
  [_label setAlpha:0.0f]; 
  } completion:nil]; 
}];
}

http://stackoverflow.com/questions/20891614/fade-in-fade-out-animation