ios - NSLayoutConstraint 抛出异常 "is not a key in the views dictionary"

Question

我正在尝试以编程方式使用自动布局并面临一些问题。我的代码很简单。我有一个 View ，我正在尝试使用 NSLayoutConstraint 添加标签，如下所示

 UILabel* downloadLabel = [[UILabel alloc] init];
 [self.leftView addSubview:downloadLabel];
 downloadLabel.translatesAutoresizingMaskIntoConstraints = NO;
 [downloadLabel setBackgroundColor:[UIColor redColor]];

  NSDictionary *downloadlabelDict = NSDictionaryOfVariableBindings(downloadLabel);
  NSArray *downloadLabelConstraint_V = [NSLayoutConstraint constraintsWithVisualFormat:@"V:[dowloadLabel(40)]"
                                                                                 options:0
                                                                                 metrics:nil
                                                                                   views:downloadlabelDict];
  NSArray *downloadLabelConstraint_H = [NSLayoutConstraint constraintsWithVisualFormat:@"H:[dowloadLabel(200)]"
                                                                                 options:0
                                                                                 metrics:nil
                                                                                   views:downloadlabelDict];


  [downloadLabel addConstraints:downloadLabelConstraint_H];
  [downloadLabel addConstraints:downloadLabelConstraint_V]; 

当我运行应用程序时，它在尝试创建第一个 NSLayoutConstraint 时抛出异常。

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Unable to parse constraint format: 
dowloadLabel is not a key in the views dictionary.V:[dowloadLabel(40)]  

Answer 1

也许您在构建约束的两行中指的是 downloadLabel 而不是 dowloadLabel？