Flutter: Firestore获取StreamBuilder内的用户uid

import 'package:flutter/material.dart';
import 'package:cloud_firestore/cloud_firestore.dart';

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return StreamBuilder<DocumentSnapshot>(
      stream: FirebaseFirestore.instance
          .collection('users')
          .doc('user_id')
          .snapshots(),
      builder: (BuildContext context, AsyncSnapshot<DocumentSnapshot> snapshot) {
        if (snapshot.hasError) {
          return Text('Error: ${snapshot.error}');
        }

        if (snapshot.connectionState == ConnectionState.waiting) {
          return Text('Loading...');
        }

        if (!snapshot.hasData) {
          return Text('No data available');
        }

        var data = snapshot.data!.data();
        var uid = data['uid'];

        return Text('User UID: $uid');
      },
    );
  }
}