通过编程将自动布局约束添加到导航控制器 [英] Adding autolayout constraints to navigation controller programmatically

问题描述

我正在尝试向在导航栏上添加的UI标签添加约束. UI标签显示正在运行的计时器

I am trying to add constraints to a UI label I added on a navigation bar. The UI label shows a running timer

这是我的代码，

self.label = [[UILabel alloc] initWithFrame:CGRectMake(550, 15, 150, 14)];
self.label.text = @"Label";
[self.label setTranslatesAutoresizingMaskIntoConstraints:NO];
[self.navigationController.navigationBar addSubview:self.label];

[self.navigationController.navigationBar addConstraint:[NSLayoutConstraint constraintWithItem:self.label
                                                       attribute:NSLayoutAttributeTrailing
                                                       relatedBy:NSLayoutRelationEqual
                                                          toItem:self.navigationController.navigationBar
                                                       attribute:NSLayoutAttributeTrailing
                                                      multiplier:1.0f
                                                        constant:-20.0f]];

但是运行应用程序时出现错误无法修改由控制器管理的UINavigationBar的约束".

But I get the error 'Cannot modify constraints for UINavigationBar managed by a controller' when I run the app.

如何添加此约束?

推荐答案

总之:不能.

导航控制器管理导航栏和可选导航工具栏的创建，配置和显示.可以自定义导航栏与外观相关的属性，但是绝对不能直接更改其框架，边界或alpha值.导航控制器使用导航项对象(UINavigationItem的实例)动态构建导航栏的内容.类)与导航堆栈上的视图控制器相关联

The navigation controller manages the creation, configuration, and display of the navigation bar and optional navigation toolbar. It is permissible to customize the navigation bar’s appearance-related properties but you must never change its frame, bounds, or alpha values directly ... A navigation controller builds the contents of the navigation bar dynamically using the navigation item objects (instances of the UINavigationItem class) associated with the view controllers on the navigation stack

来源:Apple文档

您需要将UINavigationBar子类化，然后使用initWithNavigationBarClass:toolbarClass:实例化UINavigationController来做进一步的事情.

You would need to subclass the UINavigationBar and then instantiate the UINavigationController using initWithNavigationBarClass:toolbarClass: to do something further.

尽管您正在寻找自定义导航栏的方法，但

Though if you're looking for ways to customize the navbar, UIKit User Interface Guide is a good start to know what you may be able to do. But if it's going to be a text label, consider setting the bar's title property, for example.

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