表单字段输入的Flutter Firebase验证 [英] Flutter firebase validation of form field inputs

问题描述

我是Flutter和Firebase的新手，我正在尝试验证表单中的用户输入并针对Firebase集合运行它。

I'm new to Flutter and Firebase and I am trying to validate user input from a form and run it up against a the firebase collection.

我问用户创建用户名并要验证Firebase目录中是否存在现有用户名。

I ask users to create a username and want to validate that there is not an existing username in my Firebase directory.

我从检查Flutter Firestore中是否已存在字段。我想为该方法提供一个名称，使用该名称构建一个文档列表，然后确认不存在任何文档。

I got this validation method from the discussion on Check if Field Already exists in Flutter Firestore. I want to feed the method a name, build a List of documents with that name, and confirm that none exist.

  Future<bool> doesNameAlreadyExist(String name) async {
    final QuerySnapshot result = await Firestore.instance
        .collection('user')
        .where('user_id', isEqualTo: name)
        .limit(1)
        .getDocuments();
    final List<DocumentSnapshot> documents = result.documents;
    return documents.length == 1;
  }

我希望能够在文本表单的验证器中调用此方法字段，如下所示。

I hope to be able to call this method within the validator of the text form field as I have done below.

new TextFormField(
          decoration: new InputDecoration(labelText: 'Username'),
          validator: (value) => doesNameAlreadyExist(value) ? "Username already taken" : null,
          onSaved: (value) => _username = value,
        ),

但是，这引发了一个错误，我必须为验证器使用静态类型的布尔值。

However, this throws an error that I must have a static type of bool for the validator.

我的问题：我如何（1）创建能够搜索Firebase的静态布尔方法，或者（2）如何获得与异步功能相同的功能调用（理想情况下，无需构建另一个小部件）？

My question: how can I (1) create a static boolean method that would be able to search Firebase or (2) how can I get the same functionality with the async call (ideally, without having to build another widget)?

推荐答案

将来给出then（）方法，您可以使用That。您可以将验证器方法修改为：

Future give then() Method, you can use That. You can modify your validator Method as:

validator: (value) => checkUserValue(value) ? "Username already taken" : null,


  bool _userExist = false;
  checkUserValue<bool>(String user) {
    _doesEmailAlreadyExist(user).then((val){
      if(val){
        print ("UserName Already Exits");
        _userExist = val;
      }
      else{
        print ("UserName is Available");
        _userExist = val;
      }
    });
    return _userExist;
  }

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