VFL--autolayout，autolayout

VFL--autolayout，autolayout

使用AutoLayout的時怎實現動畫

先解除約束，然後添加約束，然後layoutIfNeeded
 
autolayout旋轉螢幕時添加更新constraint怎實現？

- (void)willRotateToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation duration:(NSTimeInterval)duration { NSLayoutConstraint *con = [NSLayoutConstraint constraintWithItem:self.redView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:self.blueView attribute:NSLayoutAttributeHeight multiplier:1.2 constant:0]; if (UIInterfaceOrientationIsPortrait(toInterfaceOrientation)) { [self.view removeConstraint:con]; } else { [self.view addConstraint:con]; }}