npm install react-native-fs --save

react-native link react-native-fs

import RNFS from 'react-native-fs';

/*下載文件*/  downloadFile() {    // On Android, use "RNFS.DocumentDirectoryPath" (MainBundlePath is not defined)    // 圖片    // const downloadDest = `${RNFS.MainBundlePath}/${((Math.random() * 1000) | 0)}.jpg`;    // const formUrl = 'http://img.kaiyanapp.com/c7b46c492261a7c19fa880802afe93b3.png?imageMogr2/quality/60/format/jpg';    // 文件    // const downloadDest = `${RNFS.MainBundlePath}/${((Math.random() * 1000) | 0)}.zip`;    // const formUrl = 'http://files.cnblogs.com/zhuqil/UIWebViewDemo.zip';    // 視頻    // const downloadDest = `${RNFS.MainBundlePath}/${((Math.random() * 1000) | 0)}.mp4`;    // http://gslb.miaopai.com/stream/SnY~bbkqbi2uLEBMXHxGqnNKqyiG9ub8.mp4?vend=miaopai&    // https://gslb.miaopai.com/stream/BNaEYOL-tEwSrAiYBnPDR03dDlFavoWD.mp4?vend=miaopai&    // const formUrl = 'https://gslb.miaopai.com/stream/9Q5ADAp2v5NHtQIeQT7t461VkNPxvC2T.mp4?vend=miaopai&';    // 音頻    const downloadDest = `${RNFS.MainBundlePath}/${((Math.random() * 1000) | 0)}.mp3`;    // http://wvoice.spriteapp.cn/voice/2015/0902/55e6fc6e4f7b9.mp3    const formUrl = 'http://wvoice.spriteapp.cn/voice/2015/0818/55d2248309b09.mp3';    const options = {      fromUrl: formUrl,      toFile: downloadDest,      background: true,      begin: (res) => {        console.log('begin', res);        console.log('contentLength:', res.contentLength / 1024 / 1024, 'M');      },      progress: (res) => {        let pro = res.bytesWritten / res.contentLength;        this.setState({          progressNum: pro,        });      }    };    try {      const ret = RNFS.downloadFile(options);      ret.promise.then(res => {        console.log('success', res);        console.log('file://' + downloadDest)      }).catch(err => {        console.log('err', err);      });    }    catch (e) {      console.log(error);    }  }

 /*將文本寫入本地 txt*/  writeFile() {    // create a path you want to write to    const path = RNFS.MainBundlePath + '/test.txt';    // write the file    RNFS.writeFile(path, '這是一段文本，YES', 'utf8')      .then((success) => {        console.log('path', path);      })      .catch((err) => {        console.log(err.message);      });  }

/*讀取txt文件內容*/  readFile() {    // create a path you want to delete    const path = RNFS.MainBundlePath + '/test.txt';    return RNFS.readFile(path)      .then((result) => {        console.log(result);        this.setState({          readTxtResult: result,        })      })      .catch((err) => {        console.log(err.message);      });  }

/*在已有的txt上添加新的文本*/  appendFile() {    const path = RNFS.MainBundlePath + '/test.txt';    return RNFS.appendFile(path, '新添加的文本', 'utf8')      .then((success) => {        console.log('success');      })      .catch((err) => {        console.log(err.message);      });  }

  /*刪除文件*/  deleteFile() {    // create a path you want to delete    const path = RNFS.MainBundlePath + '/test.txt';    return RNFS.unlink(path)      .then(() => {        console.log('FILE DELETED');      })      // `unlink` will throw an error, if the item to unlink does not exist      .catch((err) => {        console.log(err.message);      });  }

 /*上傳文件 only iOS*/  uploadFile() {    const uploadSrc = `${RNFS.MainBundlePath}/test.txt`;    const uploadUrl = 'http://buz.co/rnfs/upload-tester.php';    const options = {      toUrl: uploadUrl,      files: [{name: 'myfile', filename: 'test.txt', filepath: uploadSrc, filetype: 'text/plain'}],      background: true,      method: 'POST', // PUT      begin: (res) => {        console.log('begin', res);      },      progress: (res) => {        console.log('progress', res);      }    };    const ret = RNFS.uploadFiles(options);    return ret.promise.then(res => {      const response = JSON.parse(res.body);      console.log(response);    })      .catch(err => {        console.log('err', err);      });  }