成为firstResponder在viewDidAppear中工作，但在viewDidLoad中不工作

问题描述

我的应用程序有一个模态视图控制器，包括一个搜索栏.当视图出现时，我希望搜索栏聚焦.我在viewDidLoad中尝试了[self.searchBar becomeFirstResponder]，但是没有用.后来我将其放在viewDidAppear中，它起作用了.但是，使用此替代方法，会有明显的延迟. (视图完全显示后，键盘开始出现)

My Application has a modal view controller, including a search bar. When the view comes up, I want the search bar to be focused. I tried [self.searchBar becomeFirstResponder] in viewDidLoad, but it didn't work. Later on I put it in viewDidAppear, it worked. But with this workaround, there is a visible delay. (after the view fully appeared, the keyboard began to appear)

我可以确保同时调用viewDidAppear和viewDidLoad.

I can ensure both viewDidAppear and viewDidLoad have been invoked.

如果我希望搜索栏在显示视图时立即聚焦，该怎么办?

What should I do if I want the search bar to be focused instantly with the view appear?

(我正在使用StoryBoard)

(I'm using StoryBoard)

按照答案，我尝试将代码放入viewWillLoad，但仍然无法正常工作. (在viewWillLoad中，self.searchBar.window为零)

Followed the answers, I tried to put the code in viewWillLoad, but still didn't work. (in viewWillLoad, self.searchBar.window is nil)

推荐答案

您应该在viewDidLayoutSubviews()中调用，以下设置textField的代码仅在第一次查看布局子视图时才成为FirstResponder，应该是.

You should call in viewDidLayoutSubviews(), the code below set textField becomeFirstResponder only at the first time view layout subviews, and it should be.

var isFirstLayout: Bool = true
override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    if isFirstLayout {
        defer { isFirstLayout = false }
        textField.becomeFirstResponder()
    }
}

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