AutoLayout 动画

AutoLayout 动画

how to animate constraint changes?

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• Need call layoutIfNeeded within the animation block.
• Need to call it specifically on the parent view, not the child view that has the constraints attached to it.

e.g:

- (void)moveBannerOffScreen {
    [self.view layoutIfNeeded];     // parent view call layoutIfNeeded 

    _addBannerDistanceFromBottomConstraint.constant = -32;
    [UIView animateWithDuration:5
        animations:^{
            [self.view layoutIfNeeded]; // Called within the block 
        }];
}

- (void)moveBannerOnScreen { 
    [self.view layoutIfNeeded];

    _addBannerDistanceFromBottomConstraint.constant = 0;
    [UIView animateWithDuration:5
        animations:^{
            [self.view layoutIfNeeded]; // Called on parent view
        }];
    bannerIsVisible = TRUE;
}