Immediately, cancel previous UIView animation.

Cancel_UIViewAnimation

- (void)startAnimation:(id)sender {
  UIView animateWithDuration:2.0f delay:0.0f options:UIViewAnimationCurveEaseInOut animations:^{
    _yourView.alpha = 0.0f;
  } completion:^(BOOL finished) {
    // Do something
  }];
}

- (void)stopAnimation:(id)sender {
  [UIView setAnimationBeginsFromCurrentState:YES];
  [UIView animateWithDuration:0.001 animations:^{
    _yourView.alpha = 1;
  }];
}