使用 Firebase 构建 List<FlatButton>

问题描述

我正在构建一个按钮列表，使用 Firebase 为每个按钮命名，但我的代码在将“_getbuttonbar”引用到小部件时出现此错误：“无法将参数类型‘Future’分配给参数类型“列表””。小部件也应该是 Future 吗？有人知道缺少什么吗？

class ThemesList extends StatelessWidget {
  Future<List<FlatButton>> _getbuttonbar(context) async {
    List<FlatButton> _list1 = [];
    tot = await callReadTotal(); //Receives length to make the loop.
    getListCauses(); //Calls Firebase to use arrCauses = List () for child: Text
    for (int i = 1; i <= tot; i++) {
      _list1.add(
        FlatButton(
          shape: RoundedRectangleBorder(
            borderRadius: BorderRadius.circular(30.0),side: BorderSide(color: Color.fromrGBO(150,1,1)),),splashColor: Color.fromrGBO(150,1),onpressed: () => {
            setChoice(i),Navigator.push(
              context,MaterialPageRoute(builder: (context) => CausesList()),},child: Text(
            arrCauses[i],style: TextStyle(
              color: Color.fromrGBO(150,fontSize: 20,fontFamily: 'Balsamiq_Sans',);
    }
    return _list1;
  }

  @override
  Widget build(BuildContext context) {
    return Platform.isIOS
        ? CupertinopageScaffold(child: null)
        : Scaffold(
            appBar: AppBar(
              title: Text(
                'ICare',style: TextStyle(
                  color: Color.fromrGBO(150,fontSize: 40,fontWeight: FontWeight.w500,flexibleSpace: Image(
                image: Assetimage('assets/images/solidariedade.png'),color: Color.fromrGBO(255,200,0.45),colorBlendMode: BlendMode.modulate,fit: BoxFit.cover,body: Stack(
              children: <Widget>[
                Container(
                  child: SingleChildScrollView(
                    scrollDirection: Axis.vertical,child: buttonbar(
                      children: _getbuttonbar(
                          context),//<-- Here it points out the error.
                      alignment: MainAxisAlignment.center,],);
  }
}

解决方法

您的问题可以通过两种方式解决。

通过使用 StatefulWidget

import 'package:flutter/material.dart';

class ThemesList extends StatefulWidget {
  @override
  _ThemesListState createState() => _ThemesListState();
}

class _ThemesListState extends State<ThemesList> {
  List<FlatButton> _buttonBar = [];

  @override
  void initState() {
    _getButtonBar();
    super.initState();
  }

  _getButtonBar() async {
    List<FlatButton> _list1 = [];
    tot = await callReadTotal(); //Receives length to make the loop.
    getListCauses(); //Calls Firebase to use arrCauses = List () for child: Text
    for (int i = 1; i <= tot; i++) {
      _list1.add(
        FlatButton(
          shape: RoundedRectangleBorder(
            borderRadius: BorderRadius.circular(30.0),side: BorderSide(color: Color.fromRGBO(150,1,1)),),splashColor: Color.fromRGBO(150,1),onPressed: () => {
            setChoice(i),Navigator.push(
              context,MaterialPageRoute(builder: (context) => CausesList()),},child: Text(
            arrCauses[i],style: TextStyle(
              color: Color.fromRGBO(150,fontSize: 20,fontFamily: 'Balsamiq_Sans',);
    }
    _buttonBar = _list1;
    setState(() {});
  }

  @override
  Widget build(BuildContext context) {
    return Platform.isIOS
        ? CupertinoPageScaffold(child: null)
        : Scaffold(
            appBar: AppBar(
              title: Text(
                'ICare',style: TextStyle(
                  color: Color.fromRGBO(150,fontSize: 40,fontWeight: FontWeight.w500,flexibleSpace: Image(
                image: AssetImage('assets/images/solidariedade.png'),color: Color.fromRGBO(255,200,0.45),colorBlendMode: BlendMode.modulate,fit: BoxFit.cover,body: Stack(
              children: <Widget>[
                Container(
                  child: SingleChildScrollView(
                    scrollDirection: Axis.vertical,child: ButtonBar(
                      children: _buttonBar,alignment: MainAxisAlignment.center,],);
  }
}

通过使用 FutureBuilder

import 'package:flutter/material.dart';

class ThemesList extends StatelessWidget {
  Future<List<FlatButton>> _getButtonBar(context) async {
    List<FlatButton> _list1 = [];
    tot = await callReadTotal(); //Receives length to make the loop.
    getListCauses(); //Calls Firebase to use arrCauses = List () for child: Text
    for (int i = 1; i <= tot; i++) {
      _list1.add(
        FlatButton(
          shape: RoundedRectangleBorder(
            borderRadius: BorderRadius.circular(30.0),);
    }
    return _list1;
  }

  @override
  Widget build(BuildContext context) {
    return Platform.isIOS
        ? CupertinoPageScaffold(child: null)
        : Scaffold(
            appBar: AppBar(
              title: Text(
                'ICare',child: FutureBuilder<List<FlatButton>>(
                        future: _getButtonBar(context),builder: (context,AsyncSnapshot<List<FlatButton>> snapshot) {
                          switch (snapshot.connectionState) {
                            case ConnectionState.waiting:
                              return Text('Loading....');
                              break;
                            default:
                              if (snapshot.hasError)
                                return Text('Error: ${snapshot.error}');
                              else
                                return ButtonBar(
                                  children: snapshot.data,);
                          }
                        }),);
  }
}