以编程方式将UITextField设置为FirstResponder时，会对文本编辑造成一些奇怪的操作 [英] When set UITextField as FirstResponder programmatically, cause some weird actions on text editing

问题描述

我有一个带自定义键盘的UITextField，基本上就像一个计算器。我希望我的键盘默认显示，所以我在 viewDidLoad 中使用 [self.topInputTextField becomeFirstResponder]; 认为这是非常常见的用法。但是，它会在我的文本字段上引起一些非常奇怪的操作。

I have a UITextField with custom keyboard, basically like a calculator. I would like my keyboard show up by default, so i used [self.topInputTextField becomeFirstResponder]; in viewDidLoad, I think that's very common usage. However, it causes some very weird actions on my textfield.

当我将textfield设置为viewDidLoad中的第一个响应者时，每次完成编辑后，文本将会跳转，当我单击另一个文本字段并再次单击第一个文本字段时，第一个文本字段中的文本有时会向下移动并消失，但有时不会。我觉得这很难描述，所以我为它录制了一个GIF图像。

When i set my textfield as the first responder in viewDidLoad, and every time after i done editing, the text will jump, and when i click another text field and and click the first text field again, the texts in the first text field sometimes shift down and disappear, but sometimes not. I feel it's very hard to describe, so i recorded a GIF image for it.

原因是，我确定 [self.topInputTextField becomeFirstResponder]; 导致问题，是当我评论该行代码时，一切恢复正常。这是我在评论该行后的GIF：

And the reason, that I am sure [self.topInputTextField becomeFirstResponder]; causing the issue, is when i comment that line of code out, everything back to normal. here is the GIF after i comment out that line:

这对我来说很奇怪，在2 GIF文件之间，我所做的唯一改变是注释掉那行代码。我在SE上找不到任何解决方案。任何想法都将非常感激。

that's vert strange to me, between 2 GIF file, the only change i did is comment out that line of code. I couldn't find any solution on SE. Any idea would be very appreciated.

编辑：
还有一件事是我尝试更改字体和字体大小，它们都有类似的奇怪行为。

One more thing is I tried to change font, and font sizes, they all have similar strange behaviors.

*编辑2：**
这里是我设置文本字段的方式，我没有做任何花哨的事情

*Edit 2:** here is how i set up my textfield,i didn't do anything fancy

推荐答案

尝试在 viewDidAppear 中调用键盘，在 viewDidLoad 之后调用此方法。我认为这是因为你只应该在用户看似已经加载的视图上调用键盘，所以如果你在视图实际出现之前调用它会导致意外行为。

Try calling the keyboard in viewDidAppear, this method gets called after viewDidLoad. I assume it's because you should only call the keyboard on a loaded view that has appeared to the user, so if you call it before the view actually appears it will cause unexpected behaviour.

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