Question

我不知道这是一个错误还是我做错了什么：

- (BOOL)application:(UIApplication *)application
    didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

    UIWindow *window = [self window];

    UIViewController *main = [[UIViewController alloc] init];
    UIViewController *vc1 = [[UIViewController alloc] init];
    UIViewController *vc2 = [[UIViewController alloc] init];

    [main addChildViewController:vc1];
    [main addChildViewController:vc2];

    UIView *mainView = [main view];
    UIView *v1 = [vc1 view];
    UIView *v2 = [vc2 view];

    [v1 setBackgroundColor:[UIColor redColor]];
    [v2 setBackgroundColor:[UIColor blueColor]];
    [v1 setTranslatesAutoresizingMaskIntoConstraints:NO];
    [v2 setTranslatesAutoresizingMaskIntoConstraints:NO];
    [v1 setClipsToBounds:YES];
    [v2 setClipsToBounds:YES];

    [mainView setBackgroundColor:[UIColor yellowColor]];
    [mainView addSubview:v1];
    [mainView addSubview:v2];

    NSLayoutConstraint *constraint = [NSLayoutConstraint constraintWithItem:v1
        attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual
        toItem:mainView attribute:NSLayoutAttributeTop multiplier:1.0
        constant:0.0];
    [mainView addConstraint:constraint];

    constraint = [NSLayoutConstraint constraintWithItem:v1
        attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual
        toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0
        constant:240.0];
    [mainView addConstraint:constraint];

    constraint = [NSLayoutConstraint constraintWithItem:v2
        attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual
        toItem:v1 attribute:NSLayoutAttributeBottom multiplier:1.0 constant:0.0];
    [mainView addConstraint:constraint];

    [window setRootViewController:main];
    [window setBackgroundColor:[UIColor greenColor]];
    [window makeKeyAndVisible];

    [main release];
    [vc1 release];
    [vc2 release];

    return YES;
}

当我启动应用程序时，

v1和v2无处可见。

如果我发表评论：

[v1 setTranslatesAutoresizingMaskIntoConstraints:NO];
[v2 setTranslatesAutoresizingMaskIntoConstraints:NO];

由于自动调整掩码被转换为约束，Cocoa无法满足我的约束。

Answer 1

您没有任何水平约束，并且缺少v2的高度限制。使用可视格式语言，您需要|-[v1]-|，|-[v2]-|和V:[v2]-|

等内容

NSArray *constraints;

constraints = [NSLayoutConstraint constraintsWithVisualFormat:@"|-[v1]-|" options:0 metrics:nil views:@{@"v1": v1}];
[mainView addConstraints:constraints];

当我将`translatesAutoresizingMaskIntoConstraints`设置为'NO`时，视图会消失

1 个答案: