Xamarin Forms: Issue with downloading image to device

Sreejith Sreenivasan 691 Reputation points
2023-05-01T15:22:30.17+00:00

I follow this blog to implement downloading image from URL and saving it to device.

My code:

IDownloader.cs

public interface IDownloader
{
	void DownloadFile(string url, string folder);
	event EventHandler<DownloadEventArgs> OnFileDownloaded;
}
public class DownloadEventArgs : EventArgs
{
	public bool FileSaved = false;
	public DownloadEventArgs(bool fileSaved)
	{
		FileSaved = fileSaved;
	}
}

AndroidDownloader.cs

[assembly: Dependency(typeof(AndroidDownloader))]
namespace MyApp.Droid.Renderer
{
	public class AndroidDownloader : IDownloader
	{
		public event EventHandler<DownloadEventArgs> 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));
			}
		}
	}
}

On my xaml.cs (I have added permission check on LIVE running)

IDownloader downloader = DependencyService.Get<IDownloader>();

private async void DownloadImage(object sender, EventArgs e)
{
	try
	{
		var status = await CrossPermissions.Current.CheckPermissionStatusAsync<StoragePermission>();
		if (status != PermissionStatus.Granted)
		{
			if (await CrossPermissions.Current.ShouldShowRequestPermissionRationaleAsync(Plugin.Permissions.Abstractions.Permission.Storage))
			{
				await DisplayAlert("Storage permission", "Need storage permision to download images.", "OK");
			}
			status = await CrossPermissions.Current.RequestPermissionAsync<StoragePermission>();
		}

		if (status == PermissionStatus.Granted)
		{
			downloader.DownloadFile("http://www.dada-data.net/uploads/image/hausmann_abcd.jpg", "My App");
		}
		else if (status != PermissionStatus.Unknown)
		{
			//location denied
		}
	}
	catch (Exception ex)
	{
		//Something went wrong
	}
}

private async void OnFileDownloaded(object sender, DownloadEventArgs e)
{
	await PopupNavigation.Instance.PopAsync();
	if (e.FileSaved)
	{
		UserDialogs.Instance.Toast("The image saved Successfully.");
	}
	else
	{
		UserDialogs.Instance.Toast("Error while saving the image.");
	}
}

IosDownloader.cs

[assembly: Dependency(typeof(IosDownloader))]

namespace MyApp.iOS.Renderer
{
	public class IosDownloader : IDownloader
	{
		public event EventHandler<DownloadEventArgs> 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));
			}
		}
	}

I am facing below issues:

  1. It is working on android 10 and not working on android 12. Should I add anything else for the proper working on android 12 or above?
  2. Not working on the ios platform. Added the permissions on info.plist.

UPDATE-20230205

I need to view the downloaded images on the device gallery and file manager applications.

Xamarin
Xamarin
A Microsoft open-source app platform for building Android and iOS apps with .NET and C#.
5,294 questions

1 answer

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  1. Yonglun Liu (Shanghai Wicresoft Co,.Ltd.) 35,471 Reputation points Microsoft Vendor
    2023-05-02T03:18:03.41+00:00

    Hello,

    I've modified the interface with the specific implementation method, you could refer to the following complete example:

    IDownloader.cs:

    //Since you could save pictures directly to the album after downloading, it is no longer necessary to set up folders.
public interface IDownloader 
{
    void DownloadFile(string url);
    event EventHandler<DownloadEventArgs> OnFileDownloaded;
}
public class DownloadEventArgs : EventArgs
{
    public bool FileSaved = false;
    public DownloadEventArgs(bool fileSaved)
    {
        FileSaved = fileSaved;
    }
}

    AndroidDownloader:

    [assembly: Dependency(typeof(AndroidDownloader))] 
namespace App4.Droid
{

    public class AndroidDownloader : IDownloader
    {
        public event EventHandler<DownloadEventArgs> OnFileDownloaded;
        public async void DownloadFile(string url)
        {

            try
            {
                WebClient webClient = new WebClient();
                webClient.DownloadDataCompleted += Completed;
                webClient.DownloadDataAsync(new Uri(url));
            }
            catch (System.Exception ex)
            {
                if (OnFileDownloaded != null)
                    OnFileDownloaded.Invoke(this, new DownloadEventArgs(false));
            }
        }

        private void Completed(object sender, DownloadDataCompletedEventArgs e)
        {
            if (e.Error != null)
            {
                if (OnFileDownloaded != null)
                    OnFileDownloaded.Invoke(this, new DownloadEventArgs(false));
            }
            else
            {
                
                if (OnFileDownloaded != null)
                {
                    if (Build.VERSION.SdkInt >= BuildVersionCodes.Q)
                    {
                        var contentValues = new ContentValues();
                        contentValues.Put(MediaStore.IMediaColumns.DisplayName, "test.png");
                        contentValues.Put(MediaStore.Files.IFileColumns.MimeType, "image/png");
                        contentValues.Put(MediaStore.IMediaColumns.RelativePath, "Pictures/relativePath");
                        try
                        {
                            var uri = MainActivity.Instance.ContentResolver.Insert(MediaStore.Images.Media.ExternalContentUri, contentValues);
                            var output = MainActivity.Instance.ContentResolver.OpenOutputStream(uri);
                            output.Write(e.Result, 0, e.Result.Length);
                            output.Flush();
                            output.Close();
                        }
                        catch (System.Exception ex)
                        {
                            Console.Write(ex.ToString());
                        }
                        contentValues.Put(MediaStore.IMediaColumns.IsPending, 1);
                    }
                    OnFileDownloaded.Invoke(this, new DownloadEventArgs(true));
                }
                    
            }
        }
    }
}

    Add the following permissions into AndroidManifest.xml:

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

    Add the following code into MainActivity.cs:

    public static MainActivity Instance { get; private set; } 

// Then, make the assignment in the OnCreate method. global::Xamarin.Forms.Forms.Init(this, savedInstanceState);
Instance = this;

    IosDownloader:

    
[assembly: Dependency(typeof(IosDownloader))] 
namespace App4.iOS
{
    public class IosDownloader : IDownloader
    {
        public event EventHandler<DownloadEventArgs> OnFileDownloaded;
        private string pathToNewFile;
        public void DownloadFile(string url)
        {
            try
            {
                WebClient webClient = new WebClient();
                webClient.DownloadDataCompleted += Completed;
                webClient.DownloadDataAsync(new Uri(url));
            }
            catch (System.Exception ex)
            {
                if (OnFileDownloaded != null)
                    OnFileDownloaded.Invoke(this, new DownloadEventArgs(false));
            }
        }

        private void Completed(object sender, DownloadDataCompletedEventArgs e)
        {
            if (e.Error != null)
            {
                if (OnFileDownloaded != null)
                    OnFileDownloaded.Invoke(this, new DownloadEventArgs(false));
            }
            else
            {
                
                if (OnFileDownloaded != null)
                {
                    var imageData = NSData.FromArray(e.Result);
                    var image = UIImage.LoadFromData(imageData);

                    image.SaveToPhotosAlbum((img, error) =>
                    {

                    });
                    OnFileDownloaded.Invoke(this, new DownloadEventArgs(true));
                }
                    
            }
        }
    }
}

    Add the following permission into info.plist:

    
<key>NSPhotoLibraryAddUsageDescription</key> 
<string>Please allow access to save photo in your photo library</string>

    Best Regards,

    Alec Liu.

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