在哪里添加topLayoutGuide约束代码

Question

解决方案

找出解决方案，将以下代码放在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

Apple的doc并未明确表示我应该在哪个（哪个类，哪个方法）放置这段代码（不知道self在代码中引用的内容）：

[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
];

我觉得上面的代码有一些拼写错误，所以我认为这应该是：

[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，因此在调用layoutSubviews时，可以在设置子视图时对其进行布局。如果您在viewDidLoad方法中添加此代码（我建议您将其添加到那里），则可以myViewController

替换self的出现次数