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我有一个大小为 20x40 的 UIView，它已作为 ViewController 的子视图添加。较小的 UIView 可以在屏幕上拖动，并且根据它被拖动到的位置，UIView 将重置“X”坐标以粘在屏幕边缘。

但是，我想使用/学习“自动布局”向此子视图添加约束，以在横向和纵向模式下保持相同的宽度和高度。

到目前为止的代码：

self.anotherView = [[UIView alloc] initWithFrame: CGRectMake (0.0,(self.view.frame.size.height/2)-45.0f-self.navigationController.navigationBar.frame.size.height,20.0,45.0f)];
    UIPanGestureRecognizer *panRecognizer = [[UIPanGestureRecognizer alloc]initWithTarget:self action:@selector(dragging:)];
    [self.anotherView addGestureRecognizer:panRecognizer];
    [self.anotherView setBackgroundColor: [UIColor blueColor]];
    self.anotherView.translatesAutoresizingMaskIntoConstraints = NO;

    [self.view addSubview: self.anotherView];
    [self.view bringSubviewToFront:self.anotherView];

    NSDictionary *views = @{@"subview" : self.anotherView, @"superview" : self.view};


    [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|[subview(==20)]|" options:NSLayoutFormatAlignAllBaseline metrics:nil views:views]];


    [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:[subview(==40)]" options:NSLayoutFormatAlignAllBaseline metrics:nil views:views]];


    NSLayoutConstraint *constraint = [NSLayoutConstraint constraintWithItem:self.anotherView attribute:NSLayoutAttributeBaseline relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTop multiplier:1.0 constant:self.view.bounds.size.height];
        [self.view addConstraint:constraint];

但是，上面的代码给了我以下错误：

Unable to simultaneously satisfy constraints.
    Probably at least one of the constraints in the following list is one you don't want. Try this: (1) look at each constraint and try to figure out which you don't expect; (2) find the code that added the unwanted constraint or constraints and fix it. (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) 
(
    "<NSLayoutConstraint:0x8b4ef80 H:|-(0)-[UIView:0x8b4eab0]   (Names: '|':UIView:0x8b4cc80 )>",
    "<NSLayoutConstraint:0x8b4f020 H:[UIView:0x8b4eab0(20)]>",
    "<NSLayoutConstraint:0x8b4f0f0 H:[UIView:0x8b4eab0]-(0)-|   (Names: '|':UIView:0x8b4cc80 )>",
    "<NSAutoresizingMaskLayoutConstraint:0x8aa1d30 h=--& v=--& H:[UIView:0x8b4cc80(320)]>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x8b4f0f0 H:[UIView:0x8b4eab0]-(0)-|   (Names: '|':UIView:0x8b4cc80 )>

Break on objc_exception_throw to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.

我在这里到底做错了什么？另外，我正在使用 Storyboard，只有这个视图作为子视图添加到 ViewController。请在下面找到当前 UI 外观的屏幕截图。

蓝色视图可在屏幕上自由拖动！

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1 回答 1

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[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|[subview(==20)]|" options:NSLayoutFormatAlignAllBaseline metrics:nil views:views]];

这就是说，您希望子视图的宽度为 20 点，并且还固定在超级视图的左右边缘，超级视图是表格单元格的内容视图，因此宽度为 320 点。

如果您只想限制视图的宽度，请不要在|VFL 字符串中包含超级视图指示符（方法。

要获得可变位置，您需要一个单独的约束将视图的左边缘固定到其父视图，并且constant该约束的 将随着用户拖动而更新。

于 2013-10-15T10:24:23.973 回答