Question

我需要在旋转设备时更改视图的高度。我正在storyboard使用autolayout，我在视图控制器中将高度约束设置为IBOutlet：

@property (weak, nonatomic) IBOutlet NSLayoutConstraint *passwordViewHeight;

然后，在视图控制器中我也有方法：

- (void)viewWillTransitionToSize:(CGSize)size withTransitionCoordinator:(id<UIViewControllerTransitionCoordinator>)coordinator
{
   [coordinator animateAlongsideTransition:^(id<UIViewControllerTransitionCoordinatorContext> context)
    {
        UIInterfaceOrientation orientation = [[UIApplication sharedApplication] statusBarOrientation];

        [self.view setNeedsUpdateConstraints];

    } completion:^(id<UIViewControllerTransitionCoordinatorContext> context)
    {

    }];

   [super viewWillTransitionToSize:size withTransitionCoordinator:coordinator];
}

- (void)updateViewConstraints
{
   [super updateViewConstraints];

   UIInterfaceOrientation orientation = [UIApplication sharedApplication].statusBarOrientation;

   if (orientation == UIInterfaceOrientationPortrait) {
       [self.welcomeLabel setHidden:NO];
       [self setAllPortraitConstraints];
   }
   else if ((orientation == UIInterfaceOrientationLandscapeLeft) ||
            (orientation == UIInterfaceOrientationLandscapeRight)) {
       [self.welcomeLabel setHidden:YES];
       [self setAllLandscapeConstraints];
   }
}

- (void)setAllLandscapeConstraints
{
   [self.view removeConstraint:self.passwordViewHeight];
   // More constraints

   self.passwordViewHeight = [NSLayoutConstraint constraintWithItem:self.passwordView
                                                          attribute:NSLayoutAttributeHeight
                                                          relatedBy:NSLayoutRelationEqual
                                                             toItem:nil
                                                          attribute:NSLayoutAttributeNotAnAttribute
                                                         multiplier:1.0
                                                           constant:34.0];

   // More constraints

   [self.view addConstraint:self.passwordViewHeight];
   // More constraints
}

- (void)setAllPortraitConstraints
{
   [self.view removeConstraint:self.passwordViewHeight];
   // More constraints

   self.passwordViewHeight = [NSLayoutConstraint constraintWithItem:self.passwordView
                                                          attribute:NSLayoutAttributeHeight
                                                          relatedBy:NSLayoutRelationEqual
                                                             toItem:nil
                                                          attribute:NSLayoutAttributeNotAnAttribute
                                                         multiplier:1.0
                                                           constant:40.0];

   // More constraints

   [self.view addConstraint:self.passwordViewHeight];
   // More constraints
}

然后，当我以纵向方式运行应用程序并将设备旋转到横向时，我会在Xcode中显示此登录信息：

无法同时满足约束条件。可能至少下列列表中的一个约束是您不想要的约束。试试这个：（1）看看每个约束并试着找出你不期望的东西; （2）找到添加了不需要的约束或约束的代码并修复它。（注意：如果你看到你不理解的NSAutoresizingMaskLayoutConstraints，请参阅UIView属性的文档translatesAutoresizingMaskIntoConstraints）

(
   "id: login.1, constant: 40.000000",
   "id: (null), constant: 34.000000"
)

将尝试通过违反约束来恢复 id：login.1，常量：40.000000

我想替换约束，在设备方向改变时给它一个新的常量，我做错了什么？

提前致谢

Answer 1

~~尝试在loadView或某些初始化代码中创建约束。然后将您的代码更改为：~~ 试试这个：

- (void)setAllLandscapeConstraints
{
   self.passwordViewHeight.constant = 34;
}

- (void)setAllPortraitConstraints
{
   self.passwordViewHeight.constant = 40;
}

获得“无法同时满足约束”。在旋转时更新高度约束时发出警告

1 个答案: