打开键盘会使有状态的小部件重新初始化 [英] Opening keyboard causes stateful widgets to be re-initialized

问题描述

我在稳定分支中使用Flutter 1.2.1.为了说明我的问题，想象一下我有A页和B页.A使用Navigator.push导航到B，而B使用Navigator.pop导航回到A.两者都是有状态的小部件.

I am using Flutter 1.2.1 in the Stable branch. To illustrate my problem imagine I have pages A and B. A navigates to B using Navigator.push and B navigates back to A using Navigator.pop. Both are stateful widgets.

当我从A导航到B，然后弹出回到A时，一切都很好，并且A保持其状态.但是，如果我从A导航到B，请在B中点击一个文本字段以打开键盘，然后关闭键盘并弹出回到A，A的整个状态都会刷新，并再次调用A的initState()方法.我通过使用打印语句对此进行了验证.

When I navigate from A to B and then pop back to A everything is fine and A keeps its state. However, if I navigate from A to B, tap a textfield in B opening the keyboard, then close the keyboard and pop back to A, A's entire state is refreshed and the initState() method for A is called again. I verified this by using print statements.

仅当我在弹回A之前打开键盘时才会发生这种情况.如果我导航到B，然后立即导航回A而没有任何交互，那么A会保持其状态并且不会重新初始化.

This only happens when I open the keyboard before popping back to A. If I navigate to B, then immediately navigate back to A without interacting with anything then A keeps its state and is not re-initialized.

据我了解，build方法一直被调用，但是initState()不应像这样被调用.有人知道发生了什么吗?

From my understanding the build method is called all the time but initState() should not get called like this. Does anyone know what is going on?

推荐答案

经过反复尝试，我确定了问题所在.我忘记了在MaterialApp小部件中为/路由设置了FutureBuilder.我正在传递一个函数调用，该函数返回一个Future到FutureBuilder构造函数的future参数，而不是一个指向Future的变量.

After much trial and error I determined the problem. I forgot that I had setup a FutureBuilder for the / route in my MaterialApp widget. I was passing a function call that returns a future to the future parameter of the FutureBuilder constructor rather than a variable pointing to a future.

因此，每当路线更新时，都会创建一个全新的未来.在MaterialApp构造函数之外进行函数调用并将结果的future存储在变量中，然后将其传递给FutureBuilder可以解决问题.

So every time the routes got updated a brand new future was being created. Doing the function call outside of the MaterialApp constructor and storing the resulting future in a variable, then passing that to the FutureBuilder did the trick.

这似乎与打开键盘时出现的怪异行为无关，但这绝对是原因.我的意思见下文.

It doesn't seem like this would be connected to the weird behavior I was getting when a keyboard opened, but it was definitely the cause. See below for what I mean.

有错误的代码:

return MaterialApp(
  title: appTitle,
  theme: ThemeData(
    primarySwatch: Colors.teal,
    accentColor: Colors.tealAccent,
    buttonColor: Colors.lightBlue,
  ),
  routes: {
    '/': (context) => FutureBuilder<void>(
          future: futureFun(), //Bug! I'm passing a function that returns a future when called. So a new future is returned each time
          builder: (context, snapshot) {
          ...
          }
      ...
  }
  ...
}

固定代码:

final futureVar = futureFun(); //calling the function here instead and storing its future in a variable

return MaterialApp(
  title: appTitle,
  theme: ThemeData(
    primarySwatch: Colors.teal,
    accentColor: Colors.tealAccent,
    buttonColor: Colors.lightBlue,
  ),
  routes: {
    '/': (context) => FutureBuilder<void>(
          future: futureVar, //Fixed! Passing the reference to the future rather than the function call
          builder: (context, snapshot) {
          ...
          }
      ...
  }
  ...
}

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