objective-c - 自动布局约束和 subview Controller

Question

我有两个 View Controller ，父 View Controller 和 subview Controller 。

所以在 viewDidLoad 方法中，我执行以下操作:

ChildViewController* childViewController = [[ChildViewController alloc] init];

[self addChildViewController:childViewController];

// ChildViewController sets his own constraints in viewDidLoad
[self.view addSubview:childViewController.view];

[childViewController didMoveToParentViewController:self];

//
// setup constraints to expand childViewController.view to 
// fill the size of parent view controller
//

所以基本上发生的是 updateViewConstraints 在父 Controller 约束应用之前在 ChildViewController 上调用，所以实际上 self.view.frame == CGRectZero，与我在 ChildViewController 的自定义 loadView 方法中指定。

translatesAutoresizingMaskIntoConstraints 所有 View 都设置为 NO。

在这种情况下设置约束的正确方法是什么，以便 ChildViewController 在父级之后更新他的约束？

两个 Controller 的当前日志非常令人沮丧，我不明白如何在 viewWillLayoutSubviews 之前调用 updateViewConstraints:

App[47933:c07] ChildViewController::updateViewConstraints. RECT: {{0, 0}, {0, 0}}
App[47933:c07] ParentViewController::updateViewConstraints
App[47933:c07] ChildViewController:viewWillLayoutSubviews. RECT: {{0, 0}, {984, 454}}
App[47933:c07] ChildViewController:viewDidLayoutSubviews. RECT: {{0, 0}, {984, 454}}

Answer 1

您可以在调用 addSubview: 后立即添加约束，不要忘记将 translatesAutoresizingMaskIntoConstraints 设置为 false

这是添加和隐藏带有约束的 subview Controller 的代码片段(受 apple guide 启发)

显示

private func display(contentController content : UIViewController)
    {
        self.addChildViewController(content)
        content.view.translatesAutoresizingMaskIntoConstraints = false
        self.containerView.addSubview(content.view)
        content.didMove(toParentViewController: self)

        containerView.addConstraints([
            NSLayoutConstraint(item: content.view, attribute: .top, relatedBy: .equal, toItem: containerView, attribute: .top, multiplier: 1, constant: 0),
            NSLayoutConstraint(item: content.view, attribute: .bottom, relatedBy: .equal, toItem: containerView, attribute: .bottom, multiplier: 1, constant: 0),
            NSLayoutConstraint(item: content.view, attribute: .leading, relatedBy: .equal, toItem: containerView, attribute: .leading, multiplier: 1, constant: 0),
            NSLayoutConstraint(item: content.view, attribute: .trailing, relatedBy: .equal, toItem: containerView, attribute: .trailing, multiplier: 1, constant: 0)
            ])
    }

隐藏

private func hide(contentController content : UIViewController)
    {
        content.willMove(toParentViewController: nil)
        content.view.removeFromSuperview()
        content.removeFromParentViewController()
    }