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

我的项目中包含 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 UIKeyboardWillShowNotification ，这很好。但每当我选择新的 UITextField （键盘仍在那里）时，再次调用 UIKeyboardWillShowNotification ，这是很奇怪。

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，我看到它在之前被击中了在之后调用UIKeyboardWillShowNotification !!!

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

我肯定不会调用任何 resignFirstResponder ， becomeFirstResponder ， endEditing 任何地方。 （我的意思是不要错误地打电话）

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stacktrace

Here is the stacktrace

推荐答案

问题是我为 UITextField 设置了 inputAccessoryView ，这个原因是 UIKeyboardWillShowNotification 选择新的 UITextField 时再次调用

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

本文在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的
时，会发生其他更改。在这种特殊情况下，通知行为取决于控件的inputAccessoryView属性上的
，这是显示键盘的
的原因。

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.

如果是inputAccessoryView不存在或其高度等于0
点，不发送键盘通知。我猜这是
，因为在这种情况下，应用程序中不会发生视觉变化。
否则，所有通知都按预期运行 - 这意味着当键盘显示
或隐藏在正常（未取消停靠或拆分）状态时，大多数情况下它们都是
。

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.

每当选择新的 UITextField 时，操作系统需要计算再次键盘，并发布以下通知

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失去其第一响应者状态

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

请注意，使用相同查看 inputAccessoryView 将导致 UIKeyboardWillShowNotification 仅称为一次

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

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