ios - UIView transitionFromView:toView: 和布局约束

Question

[UIView transitionFromView:toView:...]使用布局约束的正确方法是什么？

我想在约束 toView 的超级视图中安装约束。在转换调用之前我不能这样做，因为 toView 还没有超级视图。（在调用之后但在运行循环进行之前也是如此。）等到完成块安装它意味着视图将具有动画而没有约束。

Answer 1

我会使用 UIViewAnimationOptionShowHideTransitionViews 选项，它允许 toView 和 fromView 在转换之前位于视图层次结构中，但显示一个并隐藏另一个。

设置toView为隐藏，添加到superview中，在transition前安装约束。然后，您可以删除完成块中的旧视图。像这样的东西：

[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];
}];

Answer 2

在转换调用之后（但在运行循环进行之前）添加约束是有效的：我之前的测试无效:-(。对不起，噪音。

    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;
}