1、项目介绍

Flutter是目前比较流行的跨平台开发技术，凭借其出色的性能获得很多前端技术爱好者的关注，比如阿里闲鱼，美团，腾讯等大公司都有投入相关案例生产使用。
flutter_chatroom项目是基于Flutter+Dart+chewie+photo_view+image_picker等技术开发的跨平台仿微信app聊天界面应用，实现了消息/表情发送、图片预览、长按菜单、红包/小视频/朋友圈等功能。

2、技术框架

• 使用技术：Flutter 1.12.13/Dart 2.7.0
• 视频组件：chewie: ^0.9.7
• 图片/拍照：image_picker: ^0.6.6+1
• 图片预览组件：photo_view: ^0.9.2
• 弹窗组件：showModalBottomSheet/AlertDialog/SnackBar
• 本地存储：shared_preferences: ^0.5.7+1
• 字体图标：阿里iconfont字体图标库

鉴于flutter基于dart语言，需要安装Dart Sdk / Flutter Sdk，至于如何搭建开发环境，可以去官网查阅文档资料

https://flutter.cn/

https://flutterchina.club/

https://pub.flutter-io.cn/

https://www.dartcn.com/

使用vscode编辑器，可先安装Dart 、Flutter 、Flutter widget snippets等扩展插件

3、flutter沉浸式状态栏/底部tabbar

flutter中如何实现顶部全背景沉浸式透明状态栏(去掉状态栏黑色半透明背景)，去掉右上角banner，可以去看这篇文章
https://segmentfault.com/a/11...

4、flutter图标组件/IconData自定义封装组件

• 1、使用系统图标组件： Icon(Icons.search) 
• 2、使用IconData方式： Icon(IconData(0xe60e, fontFamily:'iconfont'), size:24.0)

使用第二种方式需要先下载阿里图标库字体文件，然后在pubspec.yaml中引入字体

class GStyle {
    // __ 自定义图标
    static iconfont(int codePoint, {double size = 16.0, Color color}) {
        return Icon(
            IconData(codePoint, fontFamily: 'iconfont', matchTextDirection: true),
            size: size,
            color: color,
        );
    }
}

调用非常简单，可自定义颜色、字体大小；
GStyle.iconfont(0xe635, color: Colors.orange, size: 17.0)

5、flutter实现badge红点/圆点提示

如上图：在flutter中没有圆点提示组件，需要自己封装实现；

class GStyle {
    // 消息红点
    static badge(int count, {Color color = Colors.red, bool isdot = false, double height = 18.0, double width = 18.0}) {
        final _num = count > 99 ? '···' : count;
        return Container(
            alignment: Alignment.center, height: !isdot ? height : height/2, width: !isdot ? width : width/2,
            decoration: BoxDecoration(color: color, borderRadius: BorderRadius.circular(100.0)),
            child: !isdot ? Text('$_num', style: TextStyle(color: Colors.white, fontSize: 12.0)) : null
        );
    }
}

支持自定义红点大小、颜色，默认数字超过99就...显示；
GStyle.badge(0, isdot:true)
GStyle.badge(13)
GStyle.badge(29, color: Colors.orange, height: 15.0, width: 15.0)

6、flutter长按自定义弹窗

• 在flutter中如何实现长按，并在长按位置弹出菜单，类似微信消息长按弹窗效果；

通过InkWell组件提供的onTapDown事件获取坐标点实现

InkWell(
    splashColor: Colors.grey[200],
    child: Container(...),
    onTapDown: (TapDownDetails details) {
        _globalPositionX = details.globalPosition.dx;
        _globalPositionY = details.globalPosition.dy;
    },
    onLongPress: () {
        _showPopupMenu(context);
    },
),

// 长按弹窗
double _globalPositionX = 0.0; //长按位置的横坐标
double _globalPositionY = 0.0; //长按位置的纵坐标
void _showPopupMenu(BuildContext context) {
    // 确定点击位置在左侧还是右侧
    bool isLeft = _globalPositionX > MediaQuery.of(context).size.width/2 ? false : true;
    // 确定点击位置在上半屏幕还是下半屏幕
    bool isTop = _globalPositionY > MediaQuery.of(context).size.height/2 ? false : true;

    showDialog(
      context: context,
      builder: (context) {
        return Stack(
          children: <Widget>[
            Positioned(
              top: isTop ? _globalPositionY : _globalPositionY - 200.0,
              left: isLeft ? _globalPositionX : _globalPositionX - 120.0,
              width: 120.0,
              child: Material(
                ...
              ),
            )
          ],
        );
      }
    );
}

• flutter如何实现去掉AlertDialog弹窗大小限制？

可通过SizedBox和无限制容器UnconstrainedBox组件实现

void _showCardPopup(BuildContext context) {
    showDialog(
      context: context,
      builder: (context) {
        return UnconstrainedBox(
          constrainedAxis: Axis.vertical,
          child: SizedBox(
            width: 260,
            child: AlertDialog(
              content: Container(
                ...
              ),
              elevation: 0,
              contentPadding: EdgeInsets.symmetric(horizontal: 10.0, vertical: 20.0),
            ),
          ),
        );
      }
    );
}

7、flutter登录/注册表单|本地存储

flutter提供了两个文本框组件：TextField 和 TextFormField
本文是使用TextField实现，并在文本框后添加清空文本框/密码查看图标

TextField(
  keyboardType: TextInputType.phone,
  controller: TextEditingController.fromValue(TextEditingValue(
    text: formObj['tel'],
    selection: new TextSelection.fromPosition(TextPosition(affinity: TextAffinity.downstream, offset: formObj['tel'].length))
  )),
  decoration: InputDecoration(
    hintText: "请输入手机号",
    isDense: true,
    hintStyle: TextStyle(fontSize: 14.0),
    suffixIcon: Visibility(
      visible: formObj['tel'].isNotEmpty,
      child: InkWell(
        child: GStyle.iconfont(0xe69f, color: Colors.grey, size: 14.0), onTap: () {
          setState(() { formObj['tel'] = ''; });
        }
      ),
    ),
    border: OutlineInputBorder(borderSide: BorderSide.none)
  ),
  onChanged: (val) {
    setState(() { formObj['tel'] = val; });
  },
)

TextField(
  decoration: InputDecoration(
    hintText: "请输入密码",
    isDense: true,
    hintStyle: TextStyle(fontSize: 14.0),
    suffixIcon: InkWell(
      child: Icon(formObj['isObscureText'] ? Icons.visibility_off : Icons.visibility, color: Colors.grey, size: 14.0),
      onTap: () {
        setState(() {
          formObj['isObscureText'] = !formObj['isObscureText'];
        });
      },
    ),
    border: OutlineInputBorder(borderSide: BorderSide.none)
  ),
  obscureText: formObj['isObscureText'],
  onChanged: (val) {
    setState(() { formObj['pwd'] = val; });
  },
)

验证消息提示则是使用flutter提供的SnackBar实现

// SnackBar提示
final _scaffoldkey = new GlobalKey<ScaffoldState>();
void _snackbar(String title, {Color color}) {
    _scaffoldkey.currentState.showSnackBar(SnackBar(
      backgroundColor: color ?? Colors.redAccent,
      content: Text(title),
      duration: Duration(seconds: 1),
    ));
}

另外本地存储使用的是shared\_preferences，至于如何使用可参看
https://pub.flutter-io.cn/packages/shared_preferences

void handleSubmit() async {
    if(formObj['tel'] == '') {
      _snackbar('手机号不能为空');
    }else if(!Util.checkTel(formObj['tel'])) {
      _snackbar('手机号格式有误');
    }else if(formObj['pwd'] == '') {
      _snackbar('密码不能为空');
    }else {
      // ...接口数据

      // 设置存储信息
      final prefs = await SharedPreferences.getInstance();
      prefs.setBool('hasLogin', true);
      prefs.setInt('user', int.parse(formObj['tel']));
      prefs.setString('token', Util.setToken());

      _snackbar('恭喜你，登录成功', color: Colors.greenAccent[400]);
      Timer(Duration(seconds: 2), (){
        Navigator.pushNamedAndRemoveUntil(context, '/tabbarpage', (route) => route == null);
      });
    }
}

8、flutter聊天页面功能

• 在flutter中如何实现类似上图编辑器功能？通过TextField提供的多行文本框属性maxLines就可实现。

Container(
    margin: GStyle.margin(10.0),
    decoration: BoxDecoration(color: Colors.white, borderRadius: BorderRadius.circular(3.0)),
    constraints: BoxConstraints(minHeight: 30.0, maxHeight: 150.0),
    child: TextField(
        maxLines: null,
        keyboardType: TextInputType.multiline,
        decoration: InputDecoration(
          hintStyle: TextStyle(fontSize: 14.0),
          isDense: true,
          contentPadding: EdgeInsets.all(5.0),
          border: OutlineInputBorder(borderSide: BorderSide.none)
        ),
        controller: _textEditingController,
        focusNode: _focusNode,
        onChanged: (val) {
          setState(() {
            editorLastCursor = _textEditingController.selection.baseOffset;
          });
        },
        onTap: () {handleEditorTaped();},
    ),
),

• flutter实现滚动聊天信息到最底部

通过ListView里controller属性提供的jumpTo方法及_msgController.position.maxScrollExtent

ScrollController _msgController = new ScrollController();
...
ListView(
    controller: _msgController,
    padding: EdgeInsets.all(10.0),
    children: renderMsgTpl(),
)

// 滚动消息至聊天底部
void scrollMsgBottom() {
    timer = Timer(Duration(milliseconds: 100), () => _msgController.jumpTo(_msgController.position.maxScrollExtent));
}

行了，基于flutter/dart开发聊天室实例就介绍到这里，希望能喜欢~~💪💪

最后附上electron桌面端应用实例
electron聊天室|vue+electron-vue仿微信客户端|electron桌面聊天