firebase - 在 Flutter StreamBuilder 中添加一个三元运算符或 if 运算符来检测输出文本中的条件？

Question

下面的代码是一个 StreamBuilder，它从一个流中打印多个字段。是否可以向文本小部件添加三元运算符或 if 运算符以检查结果是否大于零，如果是，则向输出添加 + 前缀？如果高于零，是否也可以将文本颜色更改为绿色，如果低于零，是否也可以将文本颜色更改为红色？

                                  Text(
                                          data['pointsfrom'].toString(),
                                          style: GoogleFonts.poppins(
                                            color: Colors.white70,
                                            fontSize: 27,
                                          ),
                                        ),

完整代码

import 'package:appforpoints/dashboardPages/adminPage/listCards/admin_notif_card.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
import 'package:font_awesome_flutter/font_awesome_flutter.dart';
import 'package:google_fonts/google_fonts.dart';

class PointsHistory extends StatefulWidget {
  final String username;
  const PointsHistory({Key? key, required this.username}) : super(key: key);

  @override
  _PointsHistoryState createState() => _PointsHistoryState();
}

class _PointsHistoryState extends State<PointsHistory> {
  @override
  void initState() {
    // TODO: implement initState
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: const Color(0xff2F3439),
      body: SizedBox(
        height: double.infinity,
        child: Padding(
          padding: const EdgeInsets.only(),
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            mainAxisAlignment: MainAxisAlignment.start,
            children: [
              Expanded(
                child: ListView(
                  scrollDirection: Axis.vertical,
                  children: [
                    Padding(
                      padding: const EdgeInsets.only(
                        top: 80,
                        left: 23,
                      ),
                      child: StreamBuilder<QuerySnapshot>(
                        stream: FirebaseFirestore.instance
                            .collection("pointslogs")
                            .where("uid",
                                isEqualTo:
                                    FirebaseAuth.instance.currentUser!.uid)
                            .where('username', isEqualTo: widget.username)
                            .orderBy('timestamp', descending: true)
                            .snapshots(),
                        builder: (BuildContext context,
                            AsyncSnapshot<QuerySnapshot> snapshot) {
                          if (snapshot.hasError) {
                            return const Text('Something went wrong');
                          }

                          if (snapshot.connectionState ==
                              ConnectionState.waiting) {
                            return const Text("Loading");
                          }
                          return Column(
                            children: snapshot.data!.docs.map(
                              (DocumentSnapshot document) {
                                Map<String, dynamic> data =
                                    document.data()! as Map<String, dynamic>;
                                return Column(
                                  children: [
                                    Row(
                                      crossAxisAlignment:
                                          CrossAxisAlignment.center,
                                      children: [
                                        Text(
                                          data['pointsfrom'].toString(),
                                          style: GoogleFonts.poppins(
                                            color: Colors.white70,
                                            fontSize: 27,
                                          ),
                                        ),
                                        Padding(
                                          padding: const EdgeInsets.only(
                                              left: 12, right: 12),
                                          child: Text(
                                            '>',
                                            style: GoogleFonts.poppins(
                                              color: Colors.white70,
                                              fontSize: 27,
                                            ),
                                          ),
                                        ),
                                        Text(
                                          data['pointsto'].toString(),
                                          style: GoogleFonts.poppins(
                                            color: Colors.white70,
                                            fontSize: 27,
                                          ),
                                        ),
                                        Padding(
                                          padding:
                                              const EdgeInsets.only(left: 20),
                                          child: Text(
                                            data['pointschange'].toString() +
                                                " ",
                                            style: GoogleFonts.poppins(
                                              color: Colors.white70,
                                              fontSize: 27,
                                            ),
                                          ),
                                        ),
                                      ],
                                    ),
                                    Row(
                                      children: [
                                        Text(
                                          data['date'].toString(),
                                        ),
                                        Text(
                                          data['time'].toString(),
                                        ),
                                      ],
                                    )
                                  ],
                                );
                              },
                            ).toList(),
                          );
                        },
                      ),
                    ),
                  ],
                ),
              ),
            ],
          ),
        ),
      ),
    );

    /*Scaffold(
      backgroundColor: const Color(0xff1e272c),
      body: ListView(
        scrollDirection: Axis.horizontal,
        children: [
          StreamBuilder<QuerySnapshot>(
            stream: userLog,
            builder:
                (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) {
              if (snapshot.hasError) {
                return const Text('Something went wrong');
              }

              if (snapshot.connectionState == ConnectionState.waiting) {
                return const Text("Loading");
              }
              return Row(
                children: snapshot.data!.docs.map(
                  (DocumentSnapshot document) {
                    Map<String, dynamic> data =
                        document.data()! as Map<String, dynamic>;
                    return Column(
                      children: [
                        Text(data['pointschange']),
                        Text(data['pointsto']),
                      ],
                    );
                  },
                ).toList(),
              );
            },
          ),
        ],
      ),
    );*/
  }
}

Answer 1

你的意思是这样的:

Text(
  (data['pointsfrom'] >= 0 ? '+' : '') + data['pointsfrom'].toString(),
  style: GoogleFonts.poppins(
    color: data['pointsfrom'] >= 0 ? Colors.green : Colors.red,
    fontSize: 27,
  ),
),

建议:我注意到您一遍又一遍地重复样式 (GoogleFonts.poppins)；您可以在构建方法的顶部设置一次，也可以创建一个单独的实用程序类，您可以在其中拥有所有这些值。您可以根据条件创建样式，您也可以将其提取为单独的方法，根据所需条件为您生成适当的样式。

您还可以将前缀逻辑移动到一个单独的方法中，这样三元操作看起来不会太乱。