UIStoryboard 如何以编程方式替换约束？

Question

我在情节提要中布置了一个视图控制器，启用了自动布局，我正在寻找一种方法来更改约束以允许我的视图旋转为横向并重新排列屏幕上的按钮。当我尝试下面的代码时，我收到大约两打“无法满足约束，打破约束......”的消息，我无法真正解码。

有没有办法用我以编程方式指定的约束动态替换情节提要中的约束？我想完全覆盖我在情节提要中定义的按钮布局。

-(void)updateViewConstraints
{
    [super updateViewConstraints];

    self.loginButton.translatesAutoresizingMaskIntoConstraints = NO;
    self.getStartedButton.translatesAutoresizingMaskIntoConstraints = NO;
    self.takeTourButton.translatesAutoresizingMaskIntoConstraints = NO;



    [self.loginButton removeConstraints:self.loginButton.constraints];
    [self.getStartedButton removeConstraints:self.getStartedButton.constraints];
    [self.takeTourButton removeConstraints:self.takeTourButton.constraints];


    one = self.loginButton;
    two = self.getStartedButton;
    three = self.takeTourButton;


    NSDictionary *metrics = @{@"height":@50.0,@"width":@100.0,@"leftSpacing":@110.0};
    NSDictionary *views = NSDictionaryOfVariableBindings(one,two,three);

    [self.view removeConstraints:activeTestLabelConstraints];
    [activeTestLabelConstraints removeAllObjects];

    if(isRotatingToLandscape)
    {

        [self registerConstraintsWithVisualFormat:@"|-[one(two)]-[two(three)]-[three]-|" options:NSLayoutFormatAlignAllTop | NSLayoutFormatAlignAllBottom metrics:metrics views:views];
        [self registerConstraintsWithVisualFormat:@"V:[one(height)]-|" options:0 metrics:metrics views:views];

    }else
    {

        [self registerConstraintsWithVisualFormat:@"|-leftSpacing-[one(width)]" options:0 metrics:metrics views:views];
        [self registerConstraintsWithVisualFormat:@"[two(width)]" options:0 metrics:metrics views:views];
        [self registerConstraintsWithVisualFormat:@"[three(width)]" options:0 metrics:metrics views:views];
        [self registerConstraintsWithVisualFormat:@"V:[one(height)]-[two(75)]-[three(100)]-|" options:NSLayoutFormatAlignAllCenterX metrics:metrics views:views];
    }


}

更新了 Rob 的回答，这是我使用的移除约束的方法

-(void)removeConstraintForView:(UIView*)viewToModify
{

    UIView* temp = viewToModify;
    [temp removeFromSuperview];
    [self.view addSubview:temp];

}

Answer 1

听起来您只想删除视图上的所有约束。由于视图上的约束通常由视图的祖先持有，因此如何轻松删除所有约束并不明显。但其实很简单。

从视图层次结构中移除一个视图会移除该视图与其外部的其他视图之间的任何约束。因此，只需从其父视图中删除您的视图，然后将其添加回来：

// Remove constraints betwixt someView and non-descendants of someView.
UIView *superview = someView.superview;
[someView removeFromSuperview];
[superview addSubview:someView];

如果someView 及其后代之间存在任何约束，则这些约束可能由someView 本身持有（但不能由someView 的任何后代持有）。如果你也想删除这些约束，你可以直接这样做：

// Remove any remaining constraints betwixt someView and its descendants.
[someView removeConstraints:[someView constraints]];