flutter简单的本地草稿箱功能

需求1：发帖退出时提示是否保存草稿
需求2：每条草稿中可以保存多张图片(最多9张)或一条视频及三十来个其它参数
需求3：每条草稿都是可以被覆盖的、可以点击删除
需求4：草稿页面可以一键清空
需求5：草稿随app删除一起没掉

看到需求第一时间想到的就是存轻量级SharedPreferences中；
行动：将图片转为base64,然后将base64转json从而实现将图片存入轻量级

/*
  * Asset类型图片转base64(其它类型替换能获取字节的对象)
  * */
  imageToUint8List(List<Asset> imageList) async {
    Completer<List<String>> _completer = Completer<List<String>>();
    List<String> dataList = [];
    if(imageList.length > 0){
      for (int i = 0; i < imageList.length; i++) {
        Asset asset = imageList[i];
        ByteData byteData = await asset.getByteData();
        var imageBase64 = base64.encode(Uint8List.view(byteData.buffer));
        dataList.add(imageBase64);
      }
      _completer.complete(dataList);
    }
    return _completer.future;
  }

结果：行不通。转换加储存极易造成内存泄漏且耗时太多（一张图片都有可能10mb以上而需求更是多图）
方法：
1.在app的file目录下新建一个文件夹保存草稿箱时把图片、视频文件复制进去。
2.把普通的字符串、数字等参数和图片、视频的文件路径封装转成json字符串一起存入轻量级
封装工具

import 'dart:convert';
import 'dart:io';

import 'package:test/common/sp_util.dart';
import 'package:test/generated/l10n.dart';
import 'package:test/jade/bean/DraftsBean.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:path_provider/path_provider.dart';

class DraftsUtil{
  /*
  * 保存草稿箱提示框
  * */
  draftsSaveDialog(context, {Function callback,Function cancelCallback}) async {
    showDialog(
        context: context,
        barrierDismissible: false,
        builder: (BuildContext context) {
          return CupertinoAlertDialog(
            content: SingleChildScrollView(
              child: ListBody(
                children: <Widget>[
                  Padding(
                    child: Text(
                      S.current.tuichu,
                      style: TextStyle(fontSize: 15, color: Color(0xffea2020)),
                    ),
                    padding: EdgeInsets.only(top: 15),
                  ),
                  SizedBox(height: 10),
                  Padding(
                    child: Text(
                      '是否保存编辑到草稿箱？',
                      style: TextStyle(fontSize: 15, color: Color(0xff666666)),
                    ),
                    padding: EdgeInsets.only(bottom: 15),
                  )
                ],
              ),
            ),
            actions: <Widget>[
              CupertinoDialogAction(
                child: Text(
                  S.current.quxiao,
                  style: TextStyle(fontSize: 14, color: Color(0xff999999)),
                ),
                onPressed: () {
                  if(cancelCallback != null){
                    cancelCallback();
                  }
                  Navigator.pop(context, false);
                },
              ),
              CupertinoDialogAction(
                child: Text(
                  '保存并退出',
                  style: TextStyle(fontSize: 14, color: Color(0xff4ec6cc)),
                ),
                onPressed: () {
                  if (callback != null) {
                    callback();
                  }
                  Navigator.pop(context, false);
                },
              )
            ],
          );
        });
  }

  /*
  * 读取草稿列表数据
  * */
  readDraftsList(var userId){
    List<DraftsBean> draftsList = [];
    List<Map<dynamic, dynamic>> getDraftsList = SpUtil.getObjectList('${userId}draftsList');

    if (getDraftsList != null && getDraftsList.length > 0) {
      getDraftsList.forEach((element) {
        draftsList.add(DraftsBean(type: element['type'],paramsData: element['paramsData'],time: element['time']));
      });
    }
    return draftsList;
  }

  /*
  * 删除某一条草稿
  * */
  deleteDrafts(var userId,int index,{List<DraftsBean> draftsList}){
    if(draftsList == null){
      draftsList = [];
      List<Map<dynamic,dynamic>> _getDraftsList = SpUtil.getObjectList('${userId}draftsList');
      if (_getDraftsList != null && _getDraftsList.length > 0) {
        _getDraftsList.forEach((element) {
          draftsList.add(DraftsBean(
              type: element['type'],
              paramsData: element['paramsData'],
              time: element['time']
          ));
        });
      }
    }
    var _paramsData = json.decode(draftsList[index].paramsData);
    List <dynamic> imagePathList = _paramsData['selectImageList'];
    String videoPath = _paramsData['selectVideoPath'];
    if(imagePathList != null && imagePathList.length>0){
      imagePathList.forEach((element) {
        var imageFile = File(element);
        if(imageFile.existsSync()){
          imageFile.deleteSync();
        }
      });
    }
    if(videoPath != null){
      var videoFile = File(videoPath);
      if(videoFile.existsSync()){
        videoFile.deleteSync();
      }
    }
    draftsList.removeAt(index);
    SpUtil.putObjectList('${userId}draftsList',draftsList);
  }

  //清空草稿箱
  clearDrafts(var userId) async {
    Directory libDir = await getExternalStorageDirectory();
    String draftsPath = libDir.path + '/draftsFiles';
    var directory = Directory(draftsPath);
    try{
      bool exists = await directory.exists();
      if(exists){
        directory.deleteSync(recursive: true);
      }
    }catch(e){
      print('删除文件夹出错：${e.toString()}');
    }
    SpUtil.remove('${userId}draftsList');
  }
}

草稿箱参数对象

class DraftsBean {
  int type; //草稿类型： 0普通发帖 1 A型发帖 2 B型发帖
  String paramsData;//保存的发帖参数 json字符串
  String time; //日期

  DraftsBean({this.type, this.paramsData,this.time});

  DraftsBean.fromJson(dynamic json) {
    type = json['type'];
    paramsData = json['paramsData'];
    time = json['time'];
  }

  Map<String, dynamic> toJson() {
    final map = <String, dynamic>{};
    map['type'] = type;
    map['paramsData'] = paramsData;
    map['time'] = time;
    return map;
  }
}

引用

//草稿箱提示框
  _backDrafts(context){
    if(logic.canSaveDrafts()){
      DraftsUtil().draftsSaveDialog(context,
          cancelCallback: (){
            Navigator.of(context).pop();
          },
          callback: () async {
            print('========点击了保存草稿');
            //当前时间
            DateTime nowTime = DateTime.now();
            var _dateFormatStr = DateUtil.formatDate(nowTime, format: DateFormats.y_mo_d);

            state.selectImagePathList.clear();
            state.selectVideoPath = null;
            List<DraftsBean> draftsList = DraftsUtil().readDraftsList(logic.userInfo.user.id);

            if(state.selectImageList.length>0){
              state.selectImagePathList = await Utils().copyFile(state.selectImageList);
            }else if(state.videoPath != null){
              List<String> videoPathList = await Utils().copyFile([File(state.videoPath)]);
              state.selectVideoPath = videoPathList.first;
            }

            if(widget.draftsIndex != null ){
              //从草稿箱进来的，传递了草稿的index，先删除再插入用来覆盖该条
              DraftsUtil().deleteDrafts(logic.userInfo.user.id, widget.draftsIndex,draftsList: draftsList);
              List<DraftsBean> latestDraftsList = DraftsUtil().readDraftsList(logic.userInfo.user.id);
              latestDraftsList.insert(widget.draftsIndex, DraftsBean(
                  type: logic.state.type == 0? 1:2,
                  paramsData: json.encode(logic.paramsData()),
                  time: '$_dateFormatStr',
              ));
              SpUtil.putObjectList('${logic.userInfo.user.id}draftsList',latestDraftsList);
            }else{
              draftsList.insert(0, DraftsBean(
                  type: logic.state.type == 0? 1:2,
                  paramsData: json.encode(logic.paramsData()),
                  time: '$_dateFormatStr',
              ));
              SpUtil.putObjectList('${logic.userInfo.user.id}draftsList',draftsList);
            }
            ATuiEventBusTool.shared().fire(CommonConfig.draftsPageRefresh);
            Navigator.of(context).pop();
          });
    }else{
      Navigator.of(context).pop();
    }
  }

草稿箱列表页面

import 'dart:convert';
import 'dart:io';
import 'package:test/common/sp_util.dart';
import 'package:test/jade/bean/DraftsBean.dart';
import 'package:test/jade/configs/CommonConfig.dart';
import 'package:test/jade/configs/PathConfig.dart';
import 'package:test/jade/customWidget/EmptyWidget.dart';
import 'package:test/jade/homePage/wantHave/WantPost.dart';
import 'package:test/jade/homePage/wantHave/wantHaveLogic/WantHaveLogic.dart';
import 'package:test/jade/homePage/wantHave/wantHaveLogic/WantHavePostBinding.dart';
import 'package:test/jade/mine/drafts/DraftsUtil.dart';
import 'package:test/jade/mine/draftsVideoItemView.dart';
import 'package:test/jade/utils/JadeColors.dart';
import 'package:test/jade/utils/Utils.dart';
import 'package:test/model/user/user_info_model.dart';
import 'package:test/pages/user_share/edit/push_share_edit.dart';
import 'package:test/util/eventbustool.dart';
import 'package:test/util/navigator_util.dart';
import 'package:test/widget/custom_appbar.dart';
import 'package:city_pickers/city_pickers.dart';
import 'package:flutter/material.dart';
import 'package:flutter_screenutil/flutter_screenutil.dart';
import 'package:flutter_staggered_grid_view/flutter_staggered_grid_view.dart';
import 'package:get/get.dart';
import 'package:provider/provider.dart';

class DraftsPage extends StatefulWidget{
  @override
  State<StatefulWidget> createState() {
    // TODO: implement createState
    return _DraftsPage();
  }
}

class _DraftsPage extends State<DraftsPage>{

  String _userId;
  List<DraftsBean> _draftsList = [];
  var _eventBus;
  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    _userId = Provider.of<UserInfoModel>(context, listen: false).user?.id;
    _draftsList = DraftsUtil().readDraftsList(_userId);
    _eventBus = ATuiEventBusTool.shared().on().listen((event) {
      if(event == CommonConfig.draftsPageRefresh){
        _draftsList = DraftsUtil().readDraftsList(_userId);
        setState(() {});
      }
    });
  }

  @override
  void dispose() {
    // TODO: implement dispose
    if(_eventBus != null){
      _eventBus.cancel();
      _eventBus = null;
    }
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return Scaffold(
        backgroundColor: JadeColors.lightGrey,
        appBar: CustomAppBar(
          elevation: 0.5,
          leading: GestureDetector(
            onTap: () {
              Navigator.of(context).pop();
            },
            child: Icon(
              Icons.arrow_back_ios,
              color: Colors.black,
            ),
          ),
          title: Row(
            mainAxisAlignment: MainAxisAlignment.spaceBetween,
            children: [
              Container(),
              Container(
                margin: EdgeInsets.only(right: 34.w),
                child: Text(
                  '草稿箱',
                  style: TextStyle(color: Colors.black,fontSize: 38.sp,fontWeight: FontWeight.w400),
                ),
              ),
              GestureDetector(
                child: Container(
                  color: Colors.transparent,
                  padding: EdgeInsets.only(left: 25.w,top: 6.w,bottom: 6.w),
                  child: Text('清空',style: TextStyle(color: JadeColors.grey_2,fontSize:32.sp),),
                ),
                onTap: () async {
                  var bool = await Utils.commonDialog(context,"是否清空草稿？");
                  if (bool) {
                    DraftsUtil().clearDrafts(_userId);
                    setState(() {
                      _draftsList.clear();
                    });
                  }
                },
              )
            ],
          )
        ),
        body: _draftsList.length>0?_body(): EmptyLayout(description: '没有草稿~',),
    );
  }

  _body(){
    return Column(
      children: [
        Container(
          margin: EdgeInsets.only(left: 20.w,right: 20.w,top: 24.w,bottom: 40.w),
          alignment: Alignment.centerLeft,
          child: Text('草稿在APP卸载后会被删除，请及时发布。',style: TextStyle(color: JadeColors.grey_2,fontSize: 24.sp,),)
        ),
        Expanded(child: Container(
            margin: EdgeInsets.symmetric(horizontal: 20.w,),
            padding: EdgeInsets.only(bottom: 20.w),
            child: MasonryGridView.count(
              crossAxisCount: 2,
              itemBuilder: (BuildContext context, int index){
                var data = _draftsList[index].paramsData;
                var decodeData = json.decode(data);
                return _itemView(index,decodeData);
              },
              mainAxisSpacing: 6.0,
              crossAxisSpacing: 6.0,
              itemCount: _draftsList.length,
              shrinkWrap: true,
            )
        ))
      ],
    );
  }


  _itemView(int index,var paramsData){
    return GestureDetector(
      child: Container(
          decoration: BoxDecoration(
              color: Colors.white,
              borderRadius: BorderRadius.circular(10)
          ),
          child: Column(
            children: [
              if(paramsData['selectImageList'] != null && paramsData['selectImageList'].isNotEmpty)
                ClipRRect(
                  borderRadius: BorderRadius.only(topLeft: Radius.circular(10),topRight: Radius.circular(10)),
                  child: Image.file(
                      File(paramsData['selectImageList'][0]),
                      width: double.infinity,
                      height: index % 2 == 1?500.w : 400.w,
                      fit: BoxFit.cover,
                      frameBuilder: (context, child, frame, wasSynchronouslyLoaded){
                        if(wasSynchronouslyLoaded){
                          return child;
                        }
                        return AnimatedOpacity(
                          child: child,
                          opacity: frame == null ? 0 : 1,
                          duration: const Duration(seconds: 4),
                          curve: Curves.easeOut,
                        );
                      }
                  ),
                ),
              if(paramsData['selectVideoPath'] != null)
                DraftsVideoItemView(mediaUrl: paramsData['selectVideoPath'],currentIndex: index,),
              Container(
                  margin: EdgeInsets.only(left: 10.w,right: 10.w,top: 20.w,bottom: 20.w),
                  alignment: Alignment.centerLeft,
                  child: Text('${paramsData['articleContent']??''}',
                      style: TextStyle(fontSize: 26.sp,fontWeight: FontWeight.w600),maxLines: 2,overflow: TextOverflow.ellipsis)
              ),
              Container(
                  margin: EdgeInsets.only(left: 20.w,right: 20.w,bottom: 20.w),
                  child: Row(
                    mainAxisAlignment: MainAxisAlignment.spaceBetween,
                    children: [
                      Text('${_draftsList[index].time}',style: TextStyle(fontSize: 20.sp,color: JadeColors.grey)),
                      GestureDetector(
                        child: Container(
                          width: 32.w,
                          height: 32.w,
                          color: Colors.transparent,
                          padding: EdgeInsets.all(2),
                          child: Image.asset(PathConfig.iconDeleteGrey),
                        ),
                        onTap: () async {
                          var bool = await Utils.commonDialog(context,"是否删除草稿？");
                          if (bool) {
                            DraftsUtil().deleteDrafts(_userId,index,draftsList:_draftsList);
                            setState(() {});
                          }
                        },
                      )
                    ],
                  )
              )
            ],
          )
      ),
      onTap: (){
        switch(_draftsList[index].type){
          case 0:
            NavigatorUtil.push(PushShareEdit(
              draftsJson: _draftsList[index].paramsData,
              draftsIndex: index,
            ));
            break;
          case 1:
            Get.to(() => WantPost(),
                binding: WantHavePostBinding(), arguments: {
                  'type':0,
                  'draftsParamsJson': _draftsList[index].paramsData, //草稿箱json数据
                  'draftsIndex': index //草稿index
                });
            break;
          case 2:
            Get.to(() => WantPost(),
                binding: WantHavePostBinding(), arguments: {
                  'type':1,
                  'draftsParamsJson': _draftsList[index].paramsData, //草稿箱json数据
                  'draftsIndex': index //草稿index
                });
            break;
        }
      },
    );
  }
}