基于我之前提出的问题。
尝试转换标签的简单按钮。 我想让它缩小0.5，这个动画可以实现，但由于某种原因它也会在执行动画时移动对象。 标签会先向上跳动，然后向左移动，然后才开始缩小。
- (IBAction)btnTest:(id)sender
{
[UIView animateWithDuration:1 delay:0 options:UIViewAnimationOptionCurveEaseInOut animations:^{
lblTest.transform = CGAffineTransformScale(lblTest.transform, 0.5f,0.5f);
}completion:^(BOOL finished) {
if(finished){
NSLog(@"DONE");
}
}];
}
我假设您正在使用自动布局：在自动布局中，如果您有前导和/或顶部约束，则在使用 CGAffineTransformMakeScale 进行缩放后，前导/顶部约束将被重新应用，您的控件将移动以确保仍满足约束条件。
您可以关闭自动布局（这是简单的答案），或者：
等到 viewDidAppear（因为在 IB 中定义的约束将被应用，并且控件将放置在我们想要的位置，其 center 属性将是可靠的）；
现在，我们已经拥有了所讨论控件的 center，将前导和顶部约束替换为 NSLayoutAttributeCenterX 和 NSLayoutAttributeCenterY 约束，使用 center 属性的值来设置 NSLayoutConstraint 的 constant。
因此：
// don't try to do this in `viewDidLoad`; do it in `viewDidAppear`, where the constraints
// have already been set
- (void)viewDidAppear:(BOOL)animated
{
[super viewDidAppear:animated];
[self replaceLeadingAndTopWithCenterConstraints:self.imageView];
}
// Because our gesture recognizer scales the UIView, it's quite important to make
// sure that we don't have the customary top and leading constraints, but rather
// have constraints to the center of the view. Thus, this looks for leading constraint
// and if found, removes it, replacing it with a centerX constraint. Likewise if it
// finds a top constraint, it replaces it with a centerY constraint.
//
// Having done that, we can now do `CGAffineTransformMakeScale`, and it will keep the
// view centered when that happens, avoiding weird UX if we don't go through this
// process.
- (void)replaceLeadingAndTopWithCenterConstraints:(UIView *)subview
{
CGPoint center = subview.center;
NSLayoutConstraint *leadingConstraint = [self findConstraintOnItem:subview
attribute:NSLayoutAttributeLeading];
if (leadingConstraint)
{
NSLog(@"Found leading constraint");
[subview.superview removeConstraint:leadingConstraint];
[subview.superview addConstraint:[NSLayoutConstraint constraintWithItem:subview
attribute:NSLayoutAttributeCenterX
relatedBy:NSLayoutRelationEqual
toItem:subview.superview
attribute:NSLayoutAttributeTop
multiplier:1.0
constant:center.x]];
}
NSLayoutConstraint *topConstraint = [self findConstraintOnItem:subview
attribute:NSLayoutAttributeTop];
if (topConstraint)
{
NSLog(@"Found top constraint");
[subview.superview removeConstraint:topConstraint];
[subview.superview addConstraint:[NSLayoutConstraint constraintWithItem:subview
attribute:NSLayoutAttributeCenterY
relatedBy:NSLayoutRelationEqual
toItem:subview.superview
attribute:NSLayoutAttributeLeft
multiplier:1.0
constant:center.y]];
}
}
- (NSLayoutConstraint *)findConstraintOnItem:(UIView *)item attribute:(NSLayoutAttribute)attribute
{
// since we're looking for the item's constraints to the superview, let's
// iterate through the superview's constraints
for (NSLayoutConstraint *constraint in item.superview.constraints)
{
// I believe that the constraints to a superview generally have the
// `firstItem` equal to the subview, so we'll try that first.
if (constraint.firstItem == item && constraint.firstAttribute == attribute)
return constraint;
// While it always appears that the constraint to a superview uses the
// subview as the `firstItem`, theoretically it's possible that the two
// could be flipped around, so I'll check for that, too:
if (constraint.secondItem == item && constraint.secondAttribute == attribute)
return constraint;
}
return nil;
}
如果你这样做了，就不需要遍历所有的约束了，你现在只需要说，例如：if (self.imageViewVerticalConstraint)
{
[self.view removeConstraint:self.imageViewVerticalConstraint];
// create the new constraint here, like shown above
}
CATransform3DMakeScale，它不会自动应用约束条件，所以你看不到它像对视图应用CGAffineTransformMakeScale那样移动。但是，如果你重新应用约束条件（setNeedsLayout或者对任何UIView对象进行任何更改都可以导致约束条件被重新应用），视图就会移动。因此，如果在重新应用约束条件之前将图层的变换恢复为标识，你可能能够“偷懒”，但最好还是关闭自动布局或修复约束条件。 - Rob