c# - How to Download Image From Url and Save It to a Local SQLite Database

Question

In Xamarin, how do you download an image from a URL?

And then, how do you save the image to a local SQLite database on the device?

My Xamarin.Forms app currently follows the Xamarin Documentation to use a URL for the ImageSource property of an Image, and this works fine. But, I've noticed that every time the app launches, it re-downloads this image over the network. I'd prefer to download the image from the URL once and save it locally to the device; this method will save battery and data usage for the user.

Answer 1

Explanation

To accomplish this, we'll download the image from the Url as a byte[] using HttpClient, then save it to our local SQLite database.

Sample App

Here is a sample app that accomplishes this using Xamarin.Forms. For the best understanding, I recommend downloading the code from GitHub.

Sample Code

Download Image From Url

We will download the image as a byte[] using HttpClient. This will make it easier to store it in our SQLite Database.

    const int _downloadImageTimeoutInSeconds = 15;
    readonly HttpClient _httpClient = new HttpClient { Timeout = TimeSpan.FromSeconds(_downloadImageTimeoutInSeconds) };

    async Task<byte[]> DownloadImageAsync(string imageUrl)
    {
        try
        {
            using (var httpResponse = await _httpClient.GetAsync(imageUrl))
            {
                if (httpResponse.StatusCode == HttpStatusCode.OK)
                {
                    return await httpResponse.Content.ReadAsByteArrayAsync();
                }
                else
                {
                    //Url is Invalid
                    return null;
                }
            }
         }
         catch (Exception e)
         {
             //Handle Exception
             return null;
         }
    }

Save Model to Database

Once you've downloaded the image as a byte[], we'll store it in the SQLite database.

I've added more information about the model in the next section.

public static async Task SaveDownloadedImage(DownloadedImageModel downloadedImage)
{
    var databaseConnection = await GetDatabaseConnectionAsync();
    await databaseConnection.InsertOrReplaceAsync(downloadedImage);
}

Model

In the model, I've created a property that stores the image as a string and a read-only property that returns the Image as a Xamarin.Forms.ImageSource.

public class DownloadedImageModel
{
    [PrimaryKey]
    public string ImageUrl { get; set;}

    public byte[] DownloadedImageBlob { get; set; }

    public ImageSource DownloadedImageAsImageStreamFromBase64String
    {
        get
        {
            try
            {
                if (DownloadedImageBlob == null)
                    return null;

                var imageByteArray = DownloadedImageBlob;

                return ImageSource.FromStream(() => new MemoryStream(imageByteArray));
            }
            catch (Exception e)
            {
                Debug.WriteLine(e);
                return null;
            }
        }
    }
}