在无状态小部件中使用 TextFormField 在颤振中非常困难 [英] Using TextFormField in Stateless widget is very difficult in flutter

问题描述

我正在尝试在无状态小部件中使用 TextFormField 以及 ScopedModel 来处理其中的文本并面临以下各种问题.

I am trying to use TextFormField in a stateless widget along with ScopedModel to deal with text in it and facing various issues as follow.

1. 我尝试使用控制器作为字段，但每次我输入一些文本并在键盘上按完成时，文本都会被清除.不知道为什么.

1. I tried using controller for field, but everytime I enter some text and press done on keyboard, text gets cleared. No idea as to why.

如果我删除控制器，文本会保留在字段中，但会产生关于如何从字段中获取文本的新问题.我通过使用回调 onFieldSubmitted 解决了它.

If I remove controller, text stays in field but new problem gets created as to how to get text from field. I solved it by using callback onFieldSubmitted.

但事实证明，onFieldSubmitted 只有在我们点击键盘上的完成按钮时才会被调用.如果我在字段中输入文本而不是单击确定，而是单击另一个字段，则不会调用回调，并且我将无法跟踪用户在字段中输入的内容.

But turns out, onFieldSubmitted is only getting called when we click on done button on keyboard. If I enter text in field and instead of clicking ok, click on another field, callback won't get called and I will have no way of tracking what user has entered in field.

有什么解决办法吗?

附上问题示例代码.

  class LoginPageStateless extends StatelessWidget {

  final loginUsernameController = TextEditingController();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      resizeToAvoidBottomPadding: true,
      body: ScopedModelDescendant<AccountModel>(
        builder: (context, child, model) {
          return Form(
            //key: _formKey,
            child: Column(
              crossAxisAlignment: CrossAxisAlignment.start,
              children: <Widget>[
                TextFormField(
                  style: TextStyle(fontSize: 15.0),
                  decoration: InputDecoration(
                    labelText: 'Email id',
                    hintText: '[e-mail]',
                  ),
                  controller: loginUsernameController,
                  onFieldSubmitted: model.updateLoginUsernameText,
                ),
                TextFormField(
                  style: TextStyle(fontSize: 15.0),
                  decoration: InputDecoration(
                    labelText: 'Password',
                  ),
                  controller: loginUsernameController,
                  onFieldSubmitted: model.updateLoginUsernameText,
                  obscureText: true,
                ),
              ],
            ),
          );
        },
      ),
    );
  }
}

推荐答案

您不能也不应该使用 Stateless 小部件来存储长期变量.

You cannot and should not use Stateless widget for storing long-term variable.

问题是，这正是你想要的.TextEditingController 是一个应该在渲染之间保留的类实例.但是通过将其存储到 StatelessWidget 中，您基本上可以在每次更新后重新创建它.

The problem is, it's exactly what you are trying to. TextEditingController is a class instance that should be kept between renders. But by storing it into a StatelessWidget you basically recreate it after every update.

您应该将您的小部件转换为 Stateful.并将该控制器移动到 State 部分

You should instead convert your widget to Stateful. And move that controller into the State part

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