ios - 为什么我的约束不起作用？ iOS系统

Question

我只是想在我的 imgView 上设置宽度和高度约束。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)]];

我最终收到此错误:无法同时满足约束。我查了一下并尝试添加:

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;

但没有任何改变

Answer 1

两个问题:

1. 你确实想要:

   imgView.translatesAutoresizingMaskIntoConstraints = NO;
   

   你不想要:

   self.view.translatesAutoresizingMaskIntoConstraints = NO;
   

2. 您设置center的尝试是徒劳的，因为当应用约束时，它将会丢失。不幸的是，您没有定义约束来定义 ImageView 的位置。您可以使用下面 block 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]];