以编程方式更新高度约束

我是新的自动布局。 我从xib文件中完成了我所有的项目，但是现在我遇到了一个问题，我必须以编程方式更新视图的高度。 我已经尝试过，但现在工作。

[[self view] addConstraint:[NSLayoutConstraint constraintWithItem:loginContainer attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0f constant:loginFrame.size.height]]; 

在控制台中显示

 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:0x78724530 V:[UIView:0x790cdfb0(170)]>", "<NSLayoutConstraint:0x787da210 V:[UIView:0x790cdfb0(400)]>" ) Will attempt to recover by breaking constraint <NSLayoutConstraint:0x78724530 V:[UIView:0x790cdfb0(170)]> Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger. The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful. 

Answer 1

您不需要添加新的约束，而需要修改现有约束中的常量。

使用IBOutlet连接到Interface Builder中的约束：

 @property (nonatomic, weak) NSLayoutConstraint *heightConstraint; 

然后，当您需要以编程方式设置它时，只需在约束上设置常量属性即可：

 heightConstraint.constant = 100; 

要么

如果无法在Interface Builder中访问该笔尖，请在代码中find该约束：

 NSLayoutConstraint *heightConstraint; for (NSLayoutConstraint *constraint in myView.constraints) { if (constraint.firstAttribute == NSLayoutAttributeHeight) { heightConstraint = constraint; break; } } heightConstraint.constant = 100; 

而在Swift中：

 if let constraint = (myView.constraints.filter{$0.firstAttribute == .width}.first) { constraint.constant = 100.0 } 

Answer 2

获取高度约束的参考：在约束中单击+ Ctrl并拖放到您的类文件中：

要更新约束值：

 self.heightConstraint.constant = 300; [self.view updateConstraints]; 

Answer 3

我们来调用你的视图nibView。 所以，你正试图在视图控制器中加载视图，所以首先，在你的视图控制器中，你需要像下面一样加载它：

 [[NSBundle mainBundle] loadNibNamed:@"NibView" owner:self options:nil]; 

然后你需要告诉nibView，你不需要通过这个操作来将自动调整掩码转换成约束

 nibView.translatesAutoresizingMaskIntoConstraints = NO; 

然后，你可以添加你的约束

  NSLayoutConstraint *heightConstraint = [NSLayoutConstraint constraintWithItem:nibView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:yourValue]; 

最后只需将其添加到您的视图约束：

 [self.view addConstraint:heightConstraint]; 

你可能也需要添加一个宽度约束。