ios - 使用布局 anchor 将自定义导航栏项目居中

Question

我已经创建了一个自定义导航项(带有标题和 UISearchBar)来替换 iOS 上的标准导航标题，我正尝试使用布局 anchor 将其置于 UINavigationBar 的中心。

但是，布局约束 [self.navigationItem.titleView.centerXAnchor constraintEqualToAnchor:self.navigationController.navigationBar.centerXAnchor].active = YES; 不起作用，UIView 包含搜索栏的内容显示在 UINavigationBar 的左侧。

其他约束:

• 宽度应该是屏幕宽度的1/3
• 我想避免将宽度设置为常量以使 View 响应方向和其他布局更改

如何让导航栏项目居中？

ScreenViewController.m:

- (void) viewDidLoad {
    [super viewDidLoad];

    // Create the search bar
    self.searchBar = [SearchBar new];

    // Create a new UIView as titleView (otherwise I'm receiving an error)   
    self.navigationItem.titleView = [UIView new];

    // Add into view hierarchy and turn off auto constraints
    [self.navigationController.navigationBar addSubview:self.navigationItem.titleView];
    [self.navigationItem.titleView setTranslatesAutoresizingMaskIntoConstraints:NO];
    [self.navigationItem.titleView addSubview:self.searchBar.view];            
    [self.searchBar.view setTranslatesAutoresizingMaskIntoConstraints:NO];

    // Set anchors for the wrapping view
    [self.navigationItem.titleView.widthAnchor constraintEqualToAnchor:self.navigationController.navigationBar.widthAnchor multiplier:1.0/3.0].active = YES;
    //[self.navigationItem.titleView.heightAnchor constraintEqualToConstant:50.0].active = YES;
    [self.navigationItem.titleView.topAnchor constraintEqualToAnchor:self.navigationController.navigationBar.topAnchor].active = YES;
    [self.navigationItem.titleView.centerXAnchor constraintEqualToAnchor:self.navigationController.navigationBar.centerXAnchor].active = YES;
    [self.navigationItem.titleView.bottomAnchor constraintEqualToAnchor:self.navigationController.navigationBar.bottomAnchor].active = YES;

    // Set anchors for the search bar
    [self.searchBar.view.widthAnchor constraintEqualToAnchor:self.navigationItem.titleView.widthAnchor multiplier:1.0].active = YES;
    //[self.navigationItem.titleView.heightAnchor constraintEqualToConstant:50.0].active = YES;
    [self.searchBar.view.topAnchor constraintEqualToAnchor:self.navigationItem.titleView.topAnchor].active = YES;
    [self.searchBar.view.bottomAnchor constraintEqualToAnchor:self.navigationItem.titleView.bottomAnchor].active = YES;
    //[self.searchBar.view.leftAnchor constraintEqualToAnchor:self.navigationItem.titleView.leftAnchor].active = YES;
    //[self.searchBar.view.rightAnchor constraintEqualToAnchor:self.navigationItem.titleView.rightAnchor].active = YES;
    [self.searchBar.view.centerXAnchor constraintEqualToAnchor:self.navigationItem.titleView.centerXAnchor].active = YES;
}

预期结果:

我得到的(标题 View 不居中):

查看层次结构:

Answer 1

您正在做的事情既不可能又违法。您根本没有制作“自定义导航栏项目”(如您的标题所述)。您正在尝试将 subview 直接添加到导航栏。你不能那样做。将某些内容放入导航栏的方法是将其分配到 View Controller 的 navigationItem 中，作为栏按钮项或作为导航项的真实 titleView。 (您将您的变量称为titleView，但实际上您并没有将其设为导航项的titleView。)