UIView transitionFromView：toView：和佈局約束

Question

使用[UIView transitionFromView:toView:...]和佈局約束的正確方法是什麼？

我想在superview約束toView中安裝約束。我不能在轉換調用之前做到這一點，因爲toView還沒有超級視圖。 （在調用之後但在運行循環前進）。等待直到完成塊來安裝它意味着該視圖將具有動畫而沒有約束。

Answer 1

我會使用UIViewAnimationOptionShowHideTransitionViews選項，該選項允許toView和fromView在轉換之前處於視圖層次結構中，但顯示一個並隱藏另一個。

設置爲隱藏視圖，將其添加到超級視圖，並在轉換前安裝約束。然後，您可以刪除完成塊中的舊視圖。事情是這樣的：

[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

添加過渡調用後的約束（但運行循環之前的進展）工作原理：我之前的那個測試無效:-(抱歉噪聲

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; 
}