How To Download Files In Xamarin.Forms

Platform Support

Here, we have used DependencyService to download any file from server path because we cannot download any file directly in Xamarin.Forms. We will see the DependencyService for Android and iOS Platforms. It is similar to UWP with slight changes.

DependencyService

Xamarin.Forms allows developers to define behavior in platform-specific projects. DependencyService then finds the right platform implementation, allowing shared code to access the native functionality. To know more about DependencyService Click Here.

Without much introduction, we will skip into the coding part of this article.

Steps

I have explained the method to create DependencyService with the steps as shown in the following.

• Step 1: Creating new Xamarin.Forms Projects.
• Step 2: Setting up AndroidManifest and info.plist
• Step 3: Creating a Dependency Service for Android and iOS Platforms.
• Step 4: Implementing the functionality to download the file in PCL.

Step 1 - Creating new Xamarin.Forms Projects

Create New Project by Selecting New - Project - Select Xamarin Cross-Platform App and click OK.

Then Select Android and iOS Platforms as shown below with Code Sharing Strategy as PCL or .NET Standard and click OK.

Step 2 - Setting up AndroidManifest and info.plist

Before starting, we need to make some setup respective to the Platforms.

For Android

1. Expand your Android Project and open Properties.
2. Then add or check the following permissions.

• INTERNET
• WRITE EXTERNAL STORAGE

3. Then click Save.

For iOS

1. Expand your iOS Project and Open your Info.plist file with XML Editor.
2. Then add the following Permissions.
   
   1. <key>NSPhotoLibraryAddUsageDescription </key>
   2. <string>Need permission to save files.</string>

• It provides permission to save file.
  
  1. <key>NSPhotoLibraryUsageDescription </key>
  2. <string>Need permission to access files.</string>

• It provides permission to access files.

From iOS 11, Separate Permission Patterns are followed for saving and Accessing the Storage or Gallery.

Step 3 - Creating Dependency Service by Platform wise

In Xamarin.Forms, we need to go with dependency service to download files.

1. First, we need to create an interface in your PCL or Shared Projects. In my case, I have created an Interface named “IDownloader.cs”.
2. Then Paste the following code in that.
   
   1. public interface IDownloader
   2. {
   3. void DownloadFile(string url, string folder);
   4. event EventHandler<DownloadEventArgs> OnFileDownloaded;
   5. }

3. Here, I have create a custom event handler to notify app users about file download. You have to create a class named “DownloadEventArgs” and paste the following code.
   
   1. public class DownloadEventArgs : EventArgs
   2. {
   3. public bool FileSaved = false;
   4. public DownloadEventArgs(bool fileSaved)
   5. {
   6. FileSaved = fileSaved;
   7. }
   8. }

For Android

1. Create a class named “AndroidDownloader.cs” in your Android Project and implement the class with “IDownloader” interface created in your Portable Library.
2. We can use WebClient to download any file from the given URL. WebClient is used for both Android and iOS Platforms to download files.
3. You can find the code used in Android Platform.
   
   1. public class AndroidDownloader : IDownloader
   2. {
   3. public event EventHandler<DownloadEventArgs> OnFileDownloaded;
   5. public void DownloadFile(string url, string folder)
   6. {
   7. string pathToNewFolder = Path.Combine(Android.OS.Environment.ExternalStorageDirectory.AbsolutePath, folder);
   8. Directory.CreateDirectory(pathToNewFolder);
   10. try
   11. {
   12. WebClient webClient = new WebClient();
   13. webClient.DownloadFileCompleted += new AsyncCompletedEventHandler(Completed);
   14. string pathToNewFile = Path.Combine(pathToNewFolder, Path.GetFileName(url));
   15. webClient.DownloadFileAsync(new Uri(url), pathToNewFile);
   16. }
   17. catch (Exception ex)
   18. {
   19. if (OnFileDownloaded != null)
   20. OnFileDownloaded.Invoke(this, new DownloadEventArgs(false));
   21. }
   22. }
   24. private void Completed(object sender, AsyncCompletedEventArgs e)
   25. {
   26. if (e.Error != null)
   27. {
   28. if (OnFileDownloaded != null)
   29. OnFileDownloaded.Invoke(this, new DownloadEventArgs(false));
   30. }
   31. else
   32. {
   33. if (OnFileDownloaded != null)
   34. OnFileDownloaded.Invoke(this, new DownloadEventArgs(true));
   35. }
   36. }
   37. }