为什么每次选择另一个 TextField 时都会调用 UIKeyboardWillShowNotification? [英] Why is UIKeyboardWillShowNotification called every time another TextField is selected?

问题描述

我有一个项目，其中包含一个 UIScrollView 和许多 UITextField.

I have a project that contains a UIScrollView and many UITextField inside it.

我第一次选择UITextField，调用了UIKeyboardWillShowNotification，这很好.但是每当我选择新的 UITextField(键盘还在那里)时，UIKeyboardWillShowNotification 就会再次被调用！！！，这很奇怪.

For the first time I select a UITextField, UIKeyboardWillShowNotification is called, which is fine. But whenever I select new UITextField (THE KEYBOARD IS STILL THERE), UIKeyboardWillShowNotification is called again !!!, which is weird.

我还为 [UIResponder resignFirstResponder] 设置了一个符号断点，我看到它在 UIKeyboardWillShowNotification 被调用之前和之后被击中！！！

I also set a symbolic breakpoint for [UIResponder resignFirstResponder] and I see that it is hit before and after UIKeyboardWillShowNotification is called !!!

另一件事是 UIKeyboardWillHideNotification 仅在我点击键盘上的完成"按钮时调用

The other thing is that UIKeyboardWillHideNotification is only called when I hit the "Done" button on the keyboard

我肯定不会在任何地方调用任何 resignFirstResponder、becomeFirstResponder、endEditing.(我的意思是不要叫错)

I'm sure to not call any resignFirstResponder, becomeFirstResponder, endEditing anywhere. (I mean not call wrongly)

什么会导致这个问题?

这是堆栈跟踪

推荐答案

问题是我为 UITextField 设置了 inputAccessoryView，这导致 UIKeyboardWillShowNotification 在新的 UITextField 被选中时被再次调用

The problem is I set inputAccessoryView for the UITextField, and this cause UIKeyboardWillShowNotification being called again when new UITextField is selected

这篇文章在 iOS 上使用键盘很好地解释了这一点

This article Working With Keyboard on iOS explains this well

当我们将外部键盘连接到iPad.在这种特殊情况下，通知行为取决于在控件的 inputAccessoryView 属性上，这是原因用于显示键盘.

Additional changes take place when we connect an external keyboard to the iPad. In this particular case, the notification behavior depends on the inputAccessoryView property of the control which was the reason for displaying the keyboard.

如果 inputAccessoryView 不存在或其高度等于 0点，不发送键盘通知.我的猜测是这是因为在这种情况下，应用程序中不会发生任何视觉变化.否则，所有通知都按预期运行——这意味着它们是在显示键盘的大多数情况下被发送或隐藏在正常(非停靠或拆分)状态.

If inputAccessoryView is not present or its height is equal to 0 points, no keyboard notifications are sent. My guess is that this is because in this case, no visual changes take place in application. Otherwise, all notifications behave as expected – which means they are being sent as in the majority of cases when the keyboard is displayed or hidden in a normal (not undocked or split) state.

Whenever new UITextField is selected, the OS needs to compute the frame for the keyboard again, and the following notifications are posted

Whenever new UITextField is selected, the OS needs to compute the frame for the keyboard again, and the following notifications are posted

UIKeyboardWillChangeFrameNotification
UIKeyboardWillShowNotification
UIKeyboardDidChangeFrameNotification
UIKeyboardDidShowNotification

同样适用于 TextField 失去第一响应者状态

The same applies for when the TextField loses its first responder status

请注意，为 inputAccessoryView 使用 same 视图将导致 UIKeyboardWillShowNotification 只调用一次

Note that using the same View for inputAccessoryView will cause UIKeyboardWillShowNotification only called once

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