为什么我的约束不起作用？ iOS

Question

我只是想在我的 imgView 上设置宽度和高度限制。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)]];

我最终收到此错误：无法同时满足约束条件。我查找了 SO 并尝试添加：

imgView.translatesAutoresizingMaskIntoConstraints = NO;

和

self.view.translatesAutoresizingMaskIntoConstraints = NO;

编辑：

我只是想将 imageView 的宽度和高度设置为所需的属性。我首先尝试使用

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

但没有任何变化

Answer 1

两期：

你确实想要：

imgView.translatesAutoresizingMaskIntoConstraints = NO;

你不想：

self.view.translatesAutoresizingMaskIntoConstraints = NO;

您尝试设置 center 是徒劳的，因为在应用约束时，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来执行此操作：

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]];

为什么我的约束不起作用？ iOS

How come my constraints are not working? iOS

ios

nslayoutconstraint