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How to download files in Xamarin.Forms

xfdownload

In this article, we will learn how to download any files from online server and save the same to the local directory of the Android and iOS Phones.

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 behaviour 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.

Coding Part:

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.
pro1

Then Select Android and iOS Platforms as shown below with Code Sharing Strategy as PCL or .Net Standard and Click OK.
pro2

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 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.
    <key>NSPhotoLibraryAddUsageDescription </key>
    <string>Need permission to save files.</string>
  3. It provides permission to save file.
    <key>NSPhotoLibraryUsageDescription</key>
    <string>Need permission to access files.</string>
  4. 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 as “IDownloader.cs”.
  2. Then Paste the following code in that.
    public interface IDownloader
    {
     void DownloadFile(string url, string folder);
     event EventHandler OnFileDownloaded;
    }
  3. Here, I have create a custom event handler to notify app users about file download. You have create a class named as “DownloadEventArgs” and Paste the following code.
    public class DownloadEventArgs : EventArgs
    {
     public bool FileSaved = false;
     public DownloadEventArgs(bool fileSaved)
     {
      FileSaved = fileSaved;
     }
    }

For Android:

  1. Create a class named as “AndroidDownloader.cs” in your Android Project and implements 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.
    public class AndroidDownloader : IDownloader
    {
     public event EventHandler OnFileDownloaded;
    
     public void DownloadFile(string url, string folder)
     {
      string pathToNewFolder = Path.Combine(Android.OS.Environment.ExternalStorageDirectory.AbsolutePath, folder);
      Directory.CreateDirectory(pathToNewFolder);
    
      try
      {
       WebClient webClient = new WebClient();
       webClient.DownloadFileCompleted += new AsyncCompletedEventHandler(Completed);
       string pathToNewFile = Path.Combine(pathToNewFolder, Path.GetFileName(url));
       webClient.DownloadFileAsync(new Uri(url), pathToNewFile);
      }
      catch (Exception ex)
      {
       if (OnFileDownloaded != null)
        OnFileDownloaded.Invoke(this, new DownloadEventArgs(false));
      }
     }
    
     private void Completed(object sender, AsyncCompletedEventArgs e)
     {
      if (e.Error != null)
      {
       if (OnFileDownloaded != null)
        OnFileDownloaded.Invoke(this, new DownloadEventArgs(false));
      }
      else
      {
       if (OnFileDownloaded != null)
        OnFileDownloaded.Invoke(this, new DownloadEventArgs(true));
      }
     }
    }
  4. Here, WebClient has an async event for notifying the download event completion.
  5. The Download event is notified by invoking the custom event created with Dependency Service from Android Platform code.

For iOS:

  1. Create a class named as “iOSDownloader.cs” in your iOS Project and implements 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 iOS Platform.
    public class IosDownloader : IDownloader
    {
     public event EventHandler OnFileDownloaded;
    
     public void DownloadFile(string url, string folder)
     {
      string pathToNewFolder = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.Personal), folder);
      Directory.CreateDirectory(pathToNewFolder);
    
      try
      {
       WebClient webClient = new WebClient();
       webClient.DownloadFileCompleted += new AsyncCompletedEventHandler(Completed);
       string pathToNewFile = Path.Combine(pathToNewFolder, Path.GetFileName(url));
       webClient.DownloadFileAsync(new Uri(url), pathToNewFile);
      }
      catch (Exception ex)
      {
       if (OnFileDownloaded != null)
        OnFileDownloaded.Invoke(this, new DownloadEventArgs(false));
      }
     }
    
     private void Completed(object sender, AsyncCompletedEventArgs e)
     {
      if (e.Error != null)
      {
       if (OnFileDownloaded != null)
        OnFileDownloaded.Invoke(this, new DownloadEventArgs(false));
      }
      else
      {
       if (OnFileDownloaded != null)
        OnFileDownloaded.Invoke(this, new DownloadEventArgs(true));
      }
     }
    }
  4. Here, WebClient has an async event for notifying the download event completion.
  5. The Download event is notified by invoking the custom event created with Dependency Service from iOS Platform code.
Don’t forget to add the following lines above the namespace of your Dependency Service classes.
[assembly: Dependency(typeof(Dependency_Class_Name))]

Step 4: Implementing the functionality to download the file in PCL

The following code shows the following points – How to subscribe the download event. – How to call the download function.
public partial class MainPage : ContentPage
{
 IDownloader downloader = DependencyService.Get();
 public MainPage()
 {
  InitializeComponent();
  downloader.OnFileDownloaded += OnFileDownloaded;
 }

 private void OnFileDownloaded(object sender, DownloadEventArgs e)
 {
  if (e.FileSaved)
  {
   DisplayAlert("XF Downloader", "File Saved Successfully", "Close");
  }
  else
  {
   DisplayAlert("XF Downloader", "Error while saving the file", "Close");
  }
 }

 private void DownloadClicked(object sender, EventArgs e)
 {
  downloader.DownloadFile("http://www.dada-data.net/uploads/image/hausmann_abcd.jpg", "XF_Downloads");
 }
}

Download Code 

You can download the full source code from GitHub. If you like this article, do like, share and star the repo in GitHub.

Download file using Okio in Android


Okio is a library that complements java.io and java.nio to make it much easier to access, store, and process your data. Simply Okio is a modern I/O API for Java. 

In this post, we will see how to download image or any file using Okio. Okio is component for OkHttp

Coding Part

Create a new project in Android Studio.

Add following dependencies to your app-level build.gradle file.
compile 'com.squareup.okhttp3:okhttp:3.6.0'
Don't forget to add the following permission in your AndroidManifest.xml
<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

Implementation

Paste the following code in your Activity and Here, I have kept as MainActivity.java
public void downloadImg(View view) {
 try {
  Request request = new Request.Builder()
    .url(imageLink)
    .build();
  new OkHttpClient().newCall(request).enqueue(new Callback() {
   @Override
   public void onFailure(Call call, IOException e) {
   }

   @Override
   public void onResponse(Call call, Response response) 
    throws IOException {
    if (!folder.exists()) {
     boolean folderCreated = folder.mkdir();
     Log.v("folderCreated", folderCreated + "");
    }
    file = new File(folder.getPath() + "/savedImg.png");
    if (file.exists()) {
     boolean fileDeleted = file.delete();
     Log.v("fileDeleted", fileDeleted + "");
    }
    boolean fileCreated = file.createNewFile();
    Log.v("fileCreated", fileCreated + "");
    BufferedSink sink = Okio.buffer(Okio.sink(file));
    sink.writeAll(response.body().source());
    sink.close();
    new DownloadImage(file).execute();
   }
  });
 } catch (Exception e) {
  e.printStackTrace();
 }
}
It is similar to Java I/O API. It has two important components as BufferSource and BufferSink.
  • BufferSource is like InputStream in Java I/O API and BufferSink is like OutputStream.
  • You can view any Source as an InputStream, and you can view any InputStream as a Source. Similarly for Sink and OutputStream. 

Demo


Download Code

You can download the full source code for this tutorial from the following Github link. If you Like this tutorial, Please star it in Github.

Download From Github