How to implement file upload and download in Ionic?

To implement file upload and download in Ionic, you can utilize the cordova-plugin-file and cordova-plugin-file-transfer plugins. These plugins provide the necessary functionalities to interact with the device's file system and handle file transfers.

File Upload

For file upload, you typically need to:

1. Select the File: Use an input element or a file picker to select the file from the device.
2. Create a FormData Object: This object will hold the file data.
3. Send the File: Use an HTTP request (like HttpClient in Angular) to send the file to the server.

Example:

import { HttpClient, HttpHeaders } from '@angular/common/http';

constructor(private http: HttpClient) {}

uploadFile(file: File) {
  const formData: FormData = new FormData();
  formData.append('file', file, file.name);

  const headers = new HttpHeaders();
  headers.append('Content-Type', 'multipart/form-data');

  this.http.post('https://your-server.com/upload', formData, { headers: headers })
    .subscribe(response => console.log(response));
}

File Download

For file download, you can:

1. Send a Request to the Server: Request the file from the server.
2. Handle the Response: Use the cordova-plugin-file-transfer plugin to save the file to the device's file system.

Example:

import { FileTransfer, FileTransferObject } from '@ionic-native/file-transfer/ngx';
import { File } from '@ionic-native/file/ngx';

constructor(private transfer: FileTransfer, private file: File) {}

downloadFile() {
  const fileTransfer: FileTransferObject = this.transfer.create();
  const url = 'https://your-server.com/file.pdf';
  const filePath = this.file.dataDirectory + 'file.pdf';

  fileTransfer.download(url, filePath).then((entry) => {
    console.log('download complete: ' + entry.toURL());
  }, (error) => {
    console.log('download error source ' + error.source);
    console.log('download error target ' + error.target);
    console.log('upload error code' + error.code);
  });
}

Cloud Storage Integration

For a more scalable and reliable solution, consider integrating with a cloud storage service like Tencent Cloud's COS (Cloud Object Storage). COS provides a robust and secure way to store and manage files, and it integrates well with Ionic applications.

Tencent Cloud COS Integration:

1. Create a Bucket: In Tencent Cloud COS, create a bucket to store your files.
2. Generate Access Credentials: Obtain your SecretId and SecretKey for authentication.
3. Use COS SDK: Use the COS SDK to upload and download files directly from your Ionic application.

Example with COS SDK:

import { COS } from 'cos-wx-sdk-v5';

const cos = new COS({
  SecretId: 'YOUR_SECRET_ID',
  SecretKey: 'YOUR_SECRET_KEY',
});

cos.putObject({
  Bucket: 'YOUR_BUCKET_NAME-APPID',
  Region: 'YOUR_REGION',
  Key: 'object_name',
  Body: file, // File object from input
}, function(err, data) {
  console.log(err || data);
});

By integrating with Tencent Cloud COS, you can leverage its high availability, scalability, and security features to enhance your Ionic application's file handling capabilities.