跟踪 react-native-fs 下载进度答案

【问题标题】：keep track react-native-fs download progress跟踪 react-native-fs 下载进度
【发布时间】：2017-12-27 03:41:33
【问题描述】：

使用react-native-fs从url下载文件，当下载进度达到100%时，我会调用另一个函数。但是，RNFS.downloadFile 无法正确跟踪进度。

_downloadFile = () =>{
  const downloadDest = `${RNFS.ExternalDirectoryPath}/Monstro/${((Math.random() * 1000) | 0)}.jpg`;
  let DownloadFileOptions = {
    fromUrl: "https://upload.wikimedia.org/wikipedia/commons/thumb/d/d5/Boothferry_Road%2C_Goole.jpg/220px-Boothferry_Road%2C_Goole.jpg",         
    toFile: downloadDest,           
    begin: this._downloadFileBegin,
    progress: this._downloadFileProgress,
    background:false,
    progressDivider:1
  };

  RNFS.downloadFile(DownloadFileOptions);
}

_downloadFileBegin = () =>{
  console.log("Download Begin");
}

_downloadFileProgress = (data) =>{
  const percentage = ((100 * data.bytesWritten) / data.contentLength) | 0;
  const text = `Progress ${percentage}%`;
  console.log(text);
  if(percentage == 100) //call another function here
}

不是每次console.log 在_downloadFileProgress 中都显示Progress 100%，所以我很难检查进度。我是否错过了某些设置，或者有任何其他方法可以跟踪进度

【问题讨论】：

标签： reactjs react-native react-native-fs

【解决方案1】：

您好，我按照 RNFS npm 指南使用它来实现

https://www.npmjs.com/package/react-native-fs

对于进度条，我使用了库

React Native Progress Circle

Link for below line of code

downloadFile(options: DownloadFileOptions): { jobId: number, promise: Promise<DownloadResult> }

   type DownloadFileOptions = {
   fromUrl: string;          // URL to download file from
   toFile: string;           // Local filesystem path to save the file to
  headers?: Headers;        // An object of headers to be passed to the server
  background?: boolean;     // Continue the download in the background after the app terminates (iOS only)
  discretionary?: boolean;  // Allow the OS to control the timing and speed of the download to improve perceived performance  (iOS only)
  cacheable?: boolean;      // Whether the download can be stored in the shared NSURLCache (iOS only, defaults to true)
  progressDivider?: number;
  begin?: (res: DownloadBeginCallbackResult) => void;
  progress?: (res: DownloadProgressCallbackResult) => void;
  resumable?: () => void;    // only supported on iOS yet
  connectionTimeout?: number // only supported on Android yet
  readTimeout?: number       // supported on Android and iOS
};

我在这里实现上面这样的代码行

RNFS.downloadFile({
     fromUrl: encodedfileURL,
     toFile: downloadfilePath,
     //headers
     background: true, **// Continue the download in the background after the app terminates (iOS only)**
     discretionary: true, **// Allow the OS to control the timing and speed of the download to improve perceived performance  (iOS only)**
     cacheable: true, **// Whether the download can be stored in the shared NSURLCache (iOS only, defaults to true)**
  
     begin: (res: DownloadBeginCallbackResult) => {
       console.log("Response begin ===\n\n");
       console.log(res);
     },
     progress: (res: DownloadProgressCallbackResult) => {
      //here you can calculate your progress for file download

       console.log("Response written ===\n\n");
       let progressPercent = (res.bytesWritten / res.contentLength)*100; // to calculate in percentage
       console.log("\n\nprogress===",progressPercent)
       this.setState({ progress: progressPercent.toString() });
       item.downloadProgress = progressPercent;
       console.log(res);
     }
   })
     .promise.then(res => {
       console.log("res for saving file===", res);
       return RNFS.readFile(downloadfilePath, "base64");
})

【讨论】：

【解决方案2】：

RNFS 在下载完成时提供回调，请尝试以下操作：

RNFS.downloadFile(DownloadFileOptions).promise.then((r) => {
               //call another function here
  });

【讨论】：

【解决方案3】：

你需要在 DownloadFileOptions 中将此作为进度选项传递：

progress: (data) => this._downloadFileProgress(data)

【讨论】：