加载另一个笔尖时的iOS自动布局

Question

我在故事板中有详细视图。我想在满足特定条件时在该视图中加载另一个Nib。但是，当我这样做时，自动布局一切都搞砸了你。

我试图在UIWebView上方显示UIView，就像叠加视图一样。我希望UIView在顶部和底部布局指南之间具有相同的设备比例，最大高度为400.

以下是我用来加载Nib的代码：

- (void)viewDidLoad
{
    [super viewDidLoad];
    [self.navigationController.navigationBar setTintColor:[UIColor whiteColor]];
    // Do any additional setup after loading the view, typically from a nib.

    UINib *s = [UINib nibWithNibName:@"Square1" bundle:nil];
    NSArray *array = [s instantiateWithOwner:self options:nil];
    StopView *stopView = (StopView *)[array objectAtIndex:0];

    [stopView setTranslatesAutoresizingMaskIntoConstraints:NO];
    [self.view addSubview:stopView];

    id topGuide = self.topLayoutGuide;
    id bottomGuide = self.bottomLayoutGuide;
    UIWebView *webView = self.detailWebView;

    NSDictionary *views = NSDictionaryOfVariableBindings(stopView, topGuide, bottomGuide, webView);

    // this is here to stop the auto layout from reporting that the guides has
    // ambiguous layout
    [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|[topGuide]|" options:0 metrics:nil views:views]];
    [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|[bottomGuide]|" options:0 metrics:nil views:views]];


    // center the stop view in the super view, both lines below are needed
    [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"|-(>=12)-[stopView(<=400)]-(>=12)-|"
                                                                      options: 0
                                                                      metrics:nil
                                                                        views:views]];

    // set the height to a ratio of the width
    NSLayoutConstraint *con2 = [NSLayoutConstraint constraintWithItem:stopView
                                                            attribute:NSLayoutAttributeWidth
                                                            relatedBy:0 toItem:stopView
                                                            attribute:NSLayoutAttributeHeight
                                                           multiplier:0.66667f constant:0];
    [self.view addConstraint:con2];

    // center the Stop View X,Y with the super view
    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:stopView
                                                          attribute:NSLayoutAttributeCenterX
                                                          relatedBy:NSLayoutRelationEqual
                                                             toItem:self.view
                                                          attribute:NSLayoutAttributeCenterX
                                                         multiplier:1.0f constant:0]];

    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:stopView
                                                          attribute:NSLayoutAttributeCenterY
                                                          relatedBy:NSLayoutRelationEqual
                                                             toItem:self.view
                                                          attribute:NSLayoutAttributeCenterY
                                                         multiplier:1.0f constant:0]];

    NSLog(@"Calling configureView from viewDidLoad");
    [self configureView];
}

以下是一些屏幕截图：

正如您在第三个屏幕截图中看到的那样，我的背景没有显示。您可以在设计模式中看到位于顶部的UILabel的 T 。

我做错了什么？

Answer 1

对于垂直约束，您需要在字符串前放置一个“V：”。要使视图最大为400，但是对于较小的屏幕，要给出顶部和底部间距约束的最大值，则需要使用约束的优先级，

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-(>=12)-[stopView(==400@900)]-(>=12)-|"
                                                                  options: 0
                                                                  metrics:nil
                                                                    views:views]];

系统将尝试使stopView的高度尽可能接近400，同时保持与顶部和底部至少12的间距。