在哪里添加 topLayoutGuide 约束代码

Question

解决方案

想了个办法，把下面的代码放到我的子类导航控制器.m文件的viewDidLoad方法中：

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.

    if ([[[UIDevice currentDevice] systemVersion] floatValue] >= 7.0f) {
        [[self view] setTranslatesAutoresizingMaskIntoConstraints:NO];

        id topGuide = [self topLayoutGuide];
        UIView * selfView = [self view];
        NSDictionary *viewsDictionary = NSDictionaryOfVariableBindings (selfView, topGuide);
        [[[self view] window] addConstraints:
         [NSLayoutConstraint constraintsWithVisualFormat:@"V:[topGuide]-0-[selfView]"
                                             options:0
                                             metrics:nil
                                               views:viewsDictionary]
        ];
        [[[self view] window] layoutSubviews]; // You must call this method here or the system raises an exception
    }
}

原帖

苹果的doc没有说清楚我应该把这段代码放在哪里（哪个类，哪个方法）（不知道self在代码中指的是什么）：

[button setTranslatesAutoresizingMaskIntoConstraints: NO];
id topGuide = myViewController.topLayoutGuide;
NSDictionary *viewsDictionary = NSDictionaryOfVariableBindings (button, topGuide);
[myViewController.view addConstraints:
    [NSLayoutConstraint constraintsWithVisualFormat: @"V: [topGuide]-20-[button]"
                                                 options: 0
                                                 metrics: nil
                                                   views: viewsDictionary]
self.view layoutSubviews; // You must call this method here or the system raises an exception
];

而且我觉得上面那段代码有错别字，所以我认为应该是这样的：

[button setTranslatesAutoresizingMaskIntoConstraints: NO];
id topGuide = myViewController.topLayoutGuide;
NSDictionary *viewsDictionary = NSDictionaryOfVariableBindings (button, topGuide);
[myViewController.view addConstraints:
    [NSLayoutConstraint constraintsWithVisualFormat: @"V: [topGuide]-20-[button]"
                                                 options: 0
                                                 metrics: nil
                                                   views: viewsDictionary]
];
self.view.layoutSubviews; // You must call this method here or the system raises an exception

Answer 1

在这种情况下，self 可以引用视图控制器。使用此代码，您正在为其视图添加约束，因此它可以在调用layoutSubviews 时设置子视图来布局子视图。如果您在 viewDidLoad 方法中添加此代码（并且我建议您在此处添加），您可以将出现的 myViewController 替换为 self