Flutter断点续传下载

撸了一个flutter断点续传下载。

基于dio，自配。

以下是源码，自取。

import 'dart:async';
import 'dart:io';

import 'package:dio/dio.dart';

/*
 * 文件下载
 * 懒加载单例
 */
class DownLoadManage {
  //用于记录正在下载的url，避免重复下载
//  var downloadingUrls = new List();
  var downloadingUrls = new Map<String, CancelToken>();

  // 单例公开访问点
  factory DownLoadManage() => _getInstance();

  // 静态私有成员，没有初始化
  static DownLoadManage _instance;

  // 私有构造函数
  DownLoadManage._() {
    // 具体初始化代码
  }

  // 静态、同步、私有访问点
  static DownLoadManage _getInstance() {
    if (_instance == null) {
      _instance = DownLoadManage._();
    }
    return _instance;
  }

  /*
   *下载
   */
  Future download(url, savePath,
      {ProgressCallback onReceiveProgress,
      Function done,
      Function failed}) async {
    int downloadStart = 0;
    bool fileExists = false;
    File f = File(savePath);
    if (await f.exists()) {
      downloadStart = f.lengthSync();
      fileExists = true;
    }
    print("开始：" + downloadStart.toString());
    if (fileExists && downloadingUrls.containsKey(url)) {
      //正在下载
      return;
    }
    var dio = Dio();
    int contentLength = await _getContentLength(dio, url);
    if (downloadStart == contentLength) {
      //存在本地文件，命中缓存
      done();
      return;
    }