UIView transitionFromView:toView:和布局约束

Question

如何正确使用[UIView transitionFromView:toView:...]和布局约束？

我想在父视图中安装约束，以限制 toView。但是，在转换调用之前，我无法这样做，因为toView还没有superview。 (同样适用于调用之后但运行循环进展之前。) 等到完成块来安装它意味着视图将在没有约束的情况下进行动画。

- PlayfulGeek

Answer 1

我会使用UIViewAnimationOptionShowHideTransitionViews选项，它允许在转换之前将toView和fromView都存在于视图层次结构中，但只显示其中一个并隐藏另一个。

将toView设置为隐藏，在转换之前将其添加到父视图并安装约束。然后可以在完成块中删除旧视图。代码示例：

[toView setHidden: YES];
[containerView addSubview: toView];
[containerView addConstraints: [NSLayoutConstraint constraintsWithVisualFormat: @"|[toView]|" options: 0 metrics: nil views: NSDictionaryOfVariableBindings(containerView, toView)]];
[containerView addConstraints: [NSLayoutConstraint constraintsWithVisualFormat: @"V:|[toView]|" options: 0 metrics: nil views: NSDictionaryOfVariableBindings(containerView, toView)]];

[UIView transitionFromView: fromView toView: toView duration: 1.0 options: UIViewAnimationOptionTransitionFlipFromBottom | UIViewAnimationOptionShowHideTransitionViews completion:^(BOOL finished) {
    [fromView removeFromSuperview];
}];

- Peter E

---

从我所看到的情况来看，即使使用了显示/隐藏选项，fromView也会自动从父视图中移除。 - pronebird

在调用后查看视图层次结构，fromView 明显没有从 superview 中移除（至少在 iOS 6 和 iOS 7 上）。 - honus

似乎要在AutoLayout约束下使用翻转动画，我们必须设置UIViewAnimationOptionShowHideTransitionViews。 - xi.lin

Answer 2

在转换调用之后（但在运行循环继续之前）添加约束有效：我之前的测试是无效的 :-( 对于噪声感到抱歉。

    NSArray *priorConstraints = _constraints;
    [UIView transitionFromView:priorView
                        toView:newView
                        ...
                    completion:^(BOOL finished) {
                        [_containerView removeConstraints:priorConstraints];
                        ....
                    }];
    _constraints = [self constrainSubview:newView toBeCongruentWithSuperview:_containerView];


- (NSArray/*[NSLayoutConstraint]*/ *)constrainSubview:(UIView *)subview 
                           toBeCongruentWithSuperview:(UIView *)superview {
    subview.translatesAutoresizingMaskIntoConstraints = NO;
    NSDictionary *viewsDictionary = NSDictionaryOfVariableBindings(subview);

    NSArray *constraints = [NSLayoutConstraint 
                            constraintsWithVisualFormat:@"H:-(0)-[subview]-(0)-"
                            options:0
                            metrics:nil
                            views:viewsDictionary];
    constraints = [constraints arrayByAddingObjectsFromArray:
                   [NSLayoutConstraint
                    constraintsWithVisualFormat:@"V:-(0)-[subview]-(0)-"
                    options:0
                    metrics:nil
                    views:viewsDictionary]];
    [superview addConstraints:constraints];
    return constraints;
}

- PlayfulGeek