ios - Autolayout 停止 UITapGestureRecognizer？

Question

我设置了一个 UIImageView 来接受点击手势，点击后，按钮将隐藏并在同一位置显示 UIActivityIndi​​catorView。逻辑很简单。但我有两个问题:

• 我需要添加 [fb setTranslatesAutoresizingMaskIntoConstraints:NO]; 或 [loading setTranslatesAutoresizingMaskIntoConstraints:NO]; 以避免约束冲突。为了安全起见，我都加了。似乎 UIImageView 和 UIActivityIndi​​catorView 有自己的内置约束:

  "<NSLayoutConstraint:0x8d69e80 UIImageView:0x8d68700.centerX == UIView:0x8d626f0.centerX>",
  "<NSLayoutConstraint:0x8d6a0f0 UIActivityIndicatorView:0x8d629b0.centerX == UIView:0x8d626f0.centerX>",
  "<NSAutoresizingMaskLayoutConstraint:0x8b48d30 h=--& v=--& UIActivityIndicatorView:0x8d629b0.midX == + 18.5>",
  "<NSAutoresizingMaskLayoutConstraint:0x8b495f0 h=--& v=--& UIImageView:0x8d68700.midX == + 60>"
  

• 我必须注释掉 [fb
setTranslatesAutoresizingMaskIntoConstraints:NO]; 或 [loading
setTranslatesAutoresizingMaskIntoConstraints:NO];。否则，UITapGestureRecognizer 不再工作，为什么？

代码:

- (void)viewDidLoad
{
    [super viewDidLoad];

    // Do any additional setup after loading the view.

    // setup the loading activity indicator;
    loading = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];
    [self.view addSubview:loading];
    loading.hidden = YES;

    // setup the fb button
    fb = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"facebook.png"]];
    fb.userInteractionEnabled = YES;

    UITapGestureRecognizer* tap = [[UITapGestureRecognizer alloc] init];
    [tap addTarget:self action:@selector(login:)];
    [fb addGestureRecognizer:tap];

    [self.view addSubview:fb];
    fb.hidden = YES;

    NSLayoutConstraint *c;
    c = [NSLayoutConstraint constraintWithItem:fb
                                     attribute:NSLayoutAttributeCenterX
                                     relatedBy:NSLayoutRelationEqual
                                        toItem:self.view
                                     attribute:NSLayoutAttributeCenterX
                                    multiplier:1
                                      constant:0];
    [self.view addConstraint:c];
    c = [NSLayoutConstraint constraintWithItem:fb
                                     attribute:NSLayoutAttributeCenterY
                                     relatedBy:NSLayoutRelationEqual
                                        toItem:self.view
                                     attribute:NSLayoutAttributeCenterY
                                    multiplier:1
                                      constant:0];
    [self.view addConstraint:c];

    c = [NSLayoutConstraint constraintWithItem:loading
                                     attribute:NSLayoutAttributeCenterX
                                     relatedBy:NSLayoutRelationEqual
                                        toItem:self.view
                                     attribute:NSLayoutAttributeCenterX
                                    multiplier:1
                                      constant:0];
    [self.view addConstraint:c];
    c = [NSLayoutConstraint constraintWithItem:loading
                                     attribute:NSLayoutAttributeCenterY
                                     relatedBy:NSLayoutRelationEqual
                                        toItem:self.view
                                     attribute:NSLayoutAttributeCenterY
                                    multiplier:1
                                      constant:0];
    [self.view addConstraint:c];

    [fb setTranslatesAutoresizingMaskIntoConstraints:NO];
    [loading setTranslatesAutoresizingMaskIntoConstraints:NO];
    [self.view setTranslatesAutoresizingMaskIntoConstraints:NO];
}

Answer 1

您需要调用 setTranslatesAutoresizingMaskIntoConstraints:NO 因为自动调整掩码被转换为与自动布局系统冲突的约束。您通常不能将自动布局约束添加到具有自动调整大小掩码约束的 View ，否则您将陷入不兼容的约束。

您的情况的主要问题是无法确定这些问题的宽度和高度。您还需要添加宽度和高度约束。如果自动布局系统无法计算它们，则无法使用居中约束来确定布局。