更新:虽然我仍然想解决这个问题,但最终我切换到了animateWithDuration:delay:options:animations:completion:
,它的效果更好。它缺少弹簧动画提供的漂亮的“反弹”效果,但至少是可控的。
- (void)handlePanGesture:(UIPanGestureRecognizer*)gesture {
CGPoint offset = [gesture translationInView:self.view];
CGPoint velocity = [gesture velocityInView:self.view];
NSLog(@"pan gesture state: %d, offset: %f velocity: %f", gesture.state, offset.x, velocity.x);
static CGFloat initialX = 0;
switch ( gesture.state ) {
case UIGestureRecognizerStateBegan: {
initialX = self.blurView.x;
break; }
case UIGestureRecognizerStateChanged: {
self.blurView.x = initialX + offset.x;
break; }
default:
case UIGestureRecognizerStateCancelled:
case UIGestureRecognizerStateEnded: {
if ( velocity.x > 0 )
[self openMenuWithVelocity:velocity.x];
else
[self closeMenuWithVelocity:velocity.x];
break; }
}
}
- (void)openMenuWithVelocity:(CGFloat)velocity {
if ( velocity < 0 )
velocity = 1.5f;
CGFloat distance = -40 - self.blurView.x;
CGFloat distanceRatio = distance / 260;
NSLog(@"distance: %f ratio: %f", distance, distanceRatio);
[UIView animateWithDuration:(0.9f * distanceRatio) delay:0 usingSpringWithDamping:0.7 initialSpringVelocity:velocity options:UIViewAnimationOptionBeginFromCurrentState animations:^{
self.blurView.x = -40;
} completion:^(BOOL finished) {
self.isMenuOpen = YES;
}];
}