在哪里添加topLayoutGuide约束代码

解

想出一个解决scheme，将下面的代码放在我的子类浏览控制器.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 } } 

原始post

苹果公司的文档没有说清楚，哪里（哪个类，哪个方法）我应该把这段代码（不知道自己在代码中指代什么）：

 [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 ]; 

我觉得上面的代码有一些错误，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可以引用一个视图控制器。 有了这个代码，你的视图就添​​加了约束条件，所以在调用layoutSubviews时候可以设置子视图的布局。 如果你在viewDidLoad方法中添加这个代码（我build议你把它添加到那里），你可以自己replacemyViewController的出现