如何在 Flutter 中从 Firebase 获取另一个用户 ID？

Question

我正在尝试通过从 firebase 写入用户的 uid 来将用户添加到我的联系人中。我需要在文本字段中写入用户 ID，并且在按下按钮时我需要 Firebase 检查此 uid，如果它存在，我的应用程序需要将其添加到联系人中。有什么解决办法吗？ p.s 我正在制作信使应用程序，它是“添加新联系人”功能。如果有人告诉我如何使用他们的 ID 创建聊天或创建与 2 个用户相同的单独“聊天 ID”，那就太好了。顺便说一句，我正在使用实时数据库

Answer 1

要检查用户是否存在，您可以执行以下操作：

    final users = FirebaseFirestore.instance.collection('users');
    final userDoc =
        await users.doc('PUT THE UID TO SEARCH FOR HERE').get();
    if (userDoc.exists) {
     // do something
    }

要使其可重用，请将其转换为函数：

Future<bool> userExists(String uid) async {
    final users = FirebaseFirestore.instance.collection('users');
    final userDoc =
        await users.doc(uid).get();
    return userDoc.exists;
}

现在您可以使用任何 uid 调用该函数：

bool _userExists = await userExists('UID');

这是一个完整的代码示例：

import 'package:flutter/material.dart';

void main() {
  runApp(App());
}

class App extends StatefulWidget {
  @override
  _AppState createState() => new _AppState();
}

class _AppState extends State<App> {
  // This key is used to control the SnackBars
  final key = GlobalKey<ScaffoldMessengerState>();
  final textCtrlr = TextEditingController();
  bool isLoading = false;

  @override
  void dispose() {
    super.dispose();
    textCtrlr.dispose();
  }

  Future<bool> userExists(String uid) async {
    final users = FirebaseFirestore.instance.collection('users');
    final userDoc = await users.doc(uid).get();
    return userDoc.exists;
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: ScaffoldMessenger(
        key: key, // Assign the key to the ScaffoldMessenger
        child: Scaffold(
          body: Center(
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: <Widget>[
                Padding(
                  padding: const EdgeInsets.all(8.0),
                  child: SizedBox(
                    child: TextFormField(
                      controller: textCtrlr,
                    ),
                    width: 200.0,
                  ),
                ),
                isLoading
                    ? const SizedBox(
                        child: CircularProgressIndicator(
                          strokeWidth: 2.0,
                        ),
                        width: 20.0,
                        height: 20.0,
                      )
                    : ElevatedButton(
                        onPressed: () async {
                          final uid = textCtrlr.text;

                          setState(() => isLoading = false);
                          final bool _userExists = await userExists(uid);
                          setState(() => isLoading = false);

                          if (_userExists) {
                            // The user exists and can
                            // be added to contacts
                            key.currentState?.showSnackBar(
                              SnackBar(
                                content: Text(
                                  'User added!',
                                ),
                                backgroundColor: Colors.green,
                                behavior: SnackBarBehavior.floating,
                              ),
                            );
                            return;
                          }

                          // The user doesn't exist
                          key.currentState?.showSnackBar(
                            SnackBar(
                              content: Text(
                                'The user doesn\'t exist',
                              ),
                              backgroundColor: Theme.of(context).errorColor,
                              behavior: SnackBarBehavior.floating,
                            ),
                          );
                        },
                        child: const Text('Search for user'),
                      ),
              ],
            ),
          ),
        ),
      ),
    );
  }
}