React native: download pdf file with rn-fetch-blob on click a button

I have to let user download a pdf file whene he clock on button, I find that I have to use rn-fetch-blob instead of react-native-fetch-blob. In the documentation there is this code:

const { config, fs } = RNFetchBlob
let DownloadDir = fs.dirs.DownloadDir // this is the Downloads directory.
let options = {
fileCache: true,
addAndroidDownloads : {
useDownloadManager : true, //uses the device's native download manager.
notification : true,
title : "Notification Title", // Title of download notification.
path: DownloadDir + "/me_"+ '.' + extension, // this is the path where your download file will be in
description : 'Downloading file.'
}
}
config(options)
.fetch('GET',"https://whatever_url_u _want/)
.then((res) => {
//console.log("Success");
})
.catch((err) => {console.log('error')}) // To execute when download cancelled and other errors
}

I have no idea what I can do with this ! how to use use it in TouchableOpacity onPress prop ? please someone can provide a detailed example

PS. I call an API with POST methode and I receive a link of PDF file. I think

I have to set this link like that
    config(options)
    .fetch('GET',this.state.data.link)

Solution

Add below permissions in AndroidManifest.xml

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.DOWNLOAD_WITHOUT_NOTIFICATION" />

To use downloadmanager, add below action in intent in AndroidManifest.xml

<intent-filter>
     <action android:name="android.intent.action.MAIN" />
     <category android:name="android.intent.category.LAUNCHER" />
     <action android:name="android.intent.action.DOWNLOAD_COMPLETE"/>                          
</intent-filter>

import PermissionsAndroid, Alert from react native (android only)

import {PermissionsAndroid, Alert} from "react-native";

Now in component

actualDownload = () => {
   const { dirs } = RNFetchBlob.fs;
  RNFetchBlob.config({
    fileCache: true,
    addAndroidDownloads: {
    useDownloadManager: true,
    notification: true,
    mediaScannable: true,
    title: `test.pdf`,
    path: `${dirs.DownloadDir}/test.pdf`,
    },
  })
    .fetch('GET', 'http://www.africau.edu/images/default/sample.pdf', {})
    .then((res) => {
      console.log('The file saved to ', res.path());
    })
    .catch((e) => {
      console.log(e)
    });
}

downloadFile = () => {
  try {
      const granted = await PermissionsAndroid.request(PermissionsAndroid.PERMISSIONS.WRITE_EXTERNAL_STORAGE);
      if (granted === PermissionsAndroid.RESULTS.GRANTED) {
        this.actualDownload();
      } else {
        Alert.alert('Permission Denied!', 'You need to give storage permission to download the file');
      }
    } catch (err) {
      console.warn(err);
    } 
}

render(){
  <TouchableOpacity onPress={this.downloadFile}>
    <Text>Download!!!</Text>
  </TouchableOpacity>
}

CAUTION: You need to ask for storage permission for android 6 or higher in runtime