Download an image from url and opening it in an image control in wp7

问题

I am making a WP7 app which download all my twitter feed. In this I want to download all the profile images and store them locally and use them, so that they would be downloaded every time i open the app. Please suggest any of the methods to do so.

What I am doing: using a WebClient to download the image

public MainPage()
    {
        InitializeComponent();

        WebClient client = new WebClient();
        client.DownloadStringCompleted += new DownloadStringCompletedEventHandler(client_DownloadStringCompleted);
        client.DownloadStringAsync(new Uri("http://www.libpng.org/pub/png/img_png/pnglogo-blk.jpg"));
    }

and store it to a file.

 void client_DownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e)
    {            
        using (IsolatedStorageFile myIsolatedStorage = IsolatedStorageFile.GetUserStoreForApplication())
        {
            if (myIsolatedStorage.FileExists(fileName1))
                myIsolatedStorage.DeleteFile(fileName1);


            var fileName1 = "Image.jpg";
            using (var fileStream = new IsolatedStorageFileStream(fileName1, FileMode.Create, myIsolatedStorage))
            {
                using (var writer = new StreamWriter(fileStream))
                {
                    var length = e.Result.Length;
                    writer.WriteLine(e.Result);
                }
                var fileStreamLength = fileStream.Length;
                fileStream.Close();
            }
        }

Now I am trying to set the image to a BitMapImage

BitmapImage bi = new BitmapImage();

using (IsolatedStorageFile myIsolatedStorage = IsolatedStorageFile.GetUserStoreForApplication())
{
    using (IsolatedStorageFileStream fileStream = myIsolatedStorage.OpenFile(fileName1, FileMode.Open, FileAccess.Read))
    {
         var fileStreamLength2 = fileStream.Length;
         bi.SetSource(fileStream);
    }
}

But I am not able to set source of the BitmapImage. It is throwing System.Exception and nothing specific. Am I doing it the right way? I mean the procedure.

EDIT Another observation is the fileStreamLength and fileStreamLength2 are different.

回答1:

You're not supposed to use DownloadString to download a binary file. Use OpenReadAsync instead, and save the binary array to the isolated storage.

DownloadString will try to convert your data to UTF-16 text, which of course can't be right when dealing with a picture.

来源：https://stackoverflow.com/questions/10319817/download-an-image-from-url-and-opening-it-in-an-image-control-in-wp7