Ios 为什么我的约束不起作用？网间网操作系统

我只是想在imgView上设置一个宽度和高度约束。我有以下代码：

UIImageView *imgView = [[UIImageView alloc] init];
imgView.center = self.view.center;
imgView.image = [UIImage imageNamed:@"favorites5-highlighted.png"];
imgView.contentMode = UIViewContentModeCenter;
[self.view addSubview:imgView];

// width constraint
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:[imgView(==100)]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(imgView)]];

// height constraint
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:[imgView(==100)]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(imgView)]];

我最终得到了这个错误：无法同时满足约束。 我抬头看了看，试图加上：

imgView.translatesAutoresizingMaskIntoConstraints = NO;

及

编辑：

我只是尝试将imageView的宽度和高度设置为所需的属性。我第一次尝试使用

CGRect rect = CGRectMake(0, 0, 10, 10);
imgView.frame = rect;

但没有任何变化

两个问题：

您确实想要：

imgView.translatesAutoresizingMaskIntoConstraints = NO;

您不希望：

self.view.translatesAutoresizingMaskIntoConstraints = NO;

您试图设置

center

的尝试是徒劳的，因为当应用约束时，这将丢失。不幸的是，您没有定义约束来定义图像视图的位置。您可以使用下面块的最后两行执行此操作：

UIImageView *imgView = [[UIImageView alloc] init];
//imgView.center = self.view.center;                                // this does nothing in auto layout
imgView.image = [UIImage imageNamed:@"favorites5-highlighted.png"];
imgView.contentMode = UIViewContentModeCenter;
imgView.translatesAutoresizingMaskIntoConstraints = NO;             // add this line
[self.view addSubview:imgView];

NSDictionary *views = NSDictionaryOfVariableBindings(imgView);

// width constraint

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:[imgView(100)]" options:0 metrics:nil views:views]];

// height constraint

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:[imgView(100)]" options:0 metrics:nil views:views]];

// center align

[self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.view attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:imgView attribute:NSLayoutAttributeCenterX multiplier:1.0 constant:0]];
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.view attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:imgView attribute:NSLayoutAttributeCenterY multiplier:1.0 constant:0]];

---

您希望进行什么更改？假设您在

viewDidLoad

中添加此代码，则应将最后两行移动到

viewDidAppear

以使其生效，此时自动布局已完成其工作，您可以应用更改。

UIImageView *imgView = [[UIImageView alloc] init];
//imgView.center = self.view.center;                                // this does nothing in auto layout
imgView.image = [UIImage imageNamed:@"favorites5-highlighted.png"];
imgView.contentMode = UIViewContentModeCenter;
imgView.translatesAutoresizingMaskIntoConstraints = NO;             // add this line
[self.view addSubview:imgView];

NSDictionary *views = NSDictionaryOfVariableBindings(imgView);

// width constraint

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:[imgView(100)]" options:0 metrics:nil views:views]];

// height constraint

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:[imgView(100)]" options:0 metrics:nil views:views]];

// center align

[self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.view attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:imgView attribute:NSLayoutAttributeCenterX multiplier:1.0 constant:0]];
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.view attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:imgView attribute:NSLayoutAttributeCenterY multiplier:1.0 constant:0]];