Troubleshooting Silverlight File Upload Errors and Fixes

How to Implement Silverlight File Upload: Step-by-Step Guide

Silverlight applications can provide rich client-side experiences, including file uploads to a server. This guide walks through a complete, practical implementation using Silverlight 5, covering client-side selection, validation, progress reporting, and server-side handling (ASP.NET). Example code snippets are included for each step.

Prerequisites

Visual Studio (2010–2015 recommended for Silverlight support).
Silverlight 5 SDK and developer runtime installed.
An ASP.NET Web Application (MVC or WebForms) for server endpoints.
Basic familiarity with C#, XAML, and HTTP.

Overview of the approach

Create a Silverlight project and host page.
Add UI for file selection and upload progress.
Use the OpenFileDialog to pick files in Silverlight.
Validate files (size, type) client-side.
Stream the file using WebClient/HttpWebRequest or WCF stream to the server.
Implement server endpoint to receive and store the file.
Report progress and handle errors.

1. Create the Silverlight project and host

In Visual Studio, create a new “Silverlight Application”. Choose to host in a new Web Application.
Ensure the Web project has an ASP.NET page (Default.aspx) that embeds the Silverlight XAP.

2. Build the UI (XAML)

Add controls: a Button to open file picker, a TextBlock for selected filename, a ProgressBar, and an Upload Button.

xml
<UserControl x:Class=“FileUploadSample.MainPage”
xmlns=“http://schemas.microsoft.com/winfx/2006/xaml/presentation”
    xmlns:x=“http://schemas.microsoft.com/winfx/2006/xaml”
    Width=“400” Height=“140”>
  <StackPanel Margin=“10” VerticalAlignment=“Top”>
    <Button x:Name=“BrowseButton” Content=“Browse…” Width=“80” Click=“BrowseButton_Click”/>
    <TextBlock x:Name=“FileNameText” Margin=“0,6,0,0”/>
    <ProgressBar x:Name=“UploadProgress” Height=“18” Width=“360” Minimum=“0” Maximum=“100” Margin=“0,6,0,0”/>
    <Button x:Name=“UploadButton” Content=“Upload” Width=“80” Click=“UploadButtonClick” Margin=“0,8,0,0”/>
    <TextBlock x:Name=“StatusText” Foreground=“Red” Margin=“0,6,0,0”/>
  </StackPanel>
</UserControl>

3. Let users pick files (OpenFileDialog)

Use OpenFileDialog to allow selection; access file(s) as StreamResourceInfo or Stream.

csharp
using System.Windows.Controls; using System.Windows; using System.IO; using System.Windows.Resources; private Stream _selectedFileStream; private string _selectedFileName; private void BrowseButton_Click(object sender, RoutedEventArgs e) { var dlg = new OpenFileDialog(); dlg.Filter = “All files (.)|.”; dlg.Multiselect = false; if (dlg.ShowDialog() == true) { var file = dlg.File; _selectedFileName = file.Name; FileNameText.Text = _selectedFileName; selectedFileStream = file.OpenRead(); // Stream of selected file StatusText.Text = ””; } }

4. Client-side validation

Check file size and extension before uploading.

csharp
private const int MaxSizeBytes = 10 1024 1024; // 10 MB private bool ValidateSelectedFile() { if (_selectedFileStream == null) { StatusText.Text = “No file selected.”; return false; } if (selectedFileStream.Length > MaxSizeBytes) { StatusText.Text = “File too large (max 10 MB).”; return false; } // optional: validate extension return true; }

5. Uploading the file from Silverlight

Two common approaches: WebClient (multipart/form-data) or HttpWebRequest with chunked streaming. WebClient is simpler but less flexible. Below is a WebClient multipart approach using a MemoryStream to build the multipart content.

csharp
using System.Net; using System.Text; private void UploadButton_Click(object sender, RoutedEventArgs e) { StatusText.Text = ””; if (!ValidateSelectedFile()) return; var client = new WebClient(); client.UploadProgressChanged += Client_UploadProgressChanged; client.UploadStringCompleted += Client_UploadStringCompleted; // Build a multipart/form-data body string boundary = ”—————————” + DateTime.Now.Ticks.ToString(“x”); client.Headers[“Content-Type”] = “multipart/form-data; boundary=” + boundary; var ms = new MemoryStream(); var writer = new StreamWriter(ms); string header = \("--{boundary} Content-Disposition: form-data; name="file"; filename="{_selectedFileName}" Content-Type: application/octet-stream "; writer.Write(header); writer.Flush(); // copy file stream _selectedFileStream.Position = 0; _selectedFileStream.CopyTo(ms); writer.Write(" "); writer.Write(\)”–{boundary}– “); writer.Flush(); ms.Position = 0; var buffer = new byte[ms.Length]; ms.Read(buffer, 0, buffer.Length); // endpoint on server Uri uri = new Uri(HtmlPage.Document.DocumentUri, ”/FileUploadHandler.ashx”); client.UploadDataAsync(uri, “POST”, buffer); }

Progress and completion handlers:

csharp
private void Client_UploadProgressChanged(object sender, UploadProgressChangedEventArgs e) { UploadProgress.Value = e.ProgressPercentage; StatusText.Text = $“Uploading… {e.ProgressPercentage}%”; } private void ClientUploadStringCompleted(object sender, UploadStringCompletedEventArgs e) { if (e.Error != null) { StatusText.Text = “Upload failed: “ + e.Error.Message; return; } StatusText.Text = “Upload complete”; }

Note: UploadDataAsync triggers UploadDataCompleted rather than UploadStringCompleted if using UploadDataAsync; adapt handlers accordingly.

Alternative: HttpWebRequest for chunked or large uploads and for reporting finer-grained progress.

6. Server-side: Receive and save the file (ASP.NET handler)

Create FileUploadHandler.ashx in the web project to accept multipart uploads.

csharp
public class FileUploadHandler : IHttpHandler { public void ProcessRequest(HttpContext context) { try { if (context.Request.Files.Count > 0) { var file = context.Request.Files[0]; string savePath = context.Server.MapPath(”~/UploadedFiles/”); if (!Directory.Exists(savePath)) Directory.CreateDirectory(savePath); string full = Path.Combine(savePath, Path.GetFileName(file.FileName)); file.SaveAs(full); context.Response.StatusCode = 200; context.Response.Write(“OK”); } else { context.Response.StatusCode = 400; context.Response.Write(“No file received”); } } catch (Exception ex) { context.Response.StatusCode = 500; context.Response.Write(“Error: “ + ex.Message); } } public bool IsReusable { get { return false; } } }

For MVC, accept via HttpPostedFileBase in a controller action.

7. Security and robustness tips

Validate file type and size on server-side too.

Store uploads outside the webroot or sanitize filenames.

Scan for malware if appropriate.

Use HTTPS to protect data in transit.

Implement authentication/authorization if uploads are restricted.

For large files, implement chunked uploads and resume support.

8. Large files and advanced scenarios

Use HttpWebRequest with BeginGetRequestStream/BeginGetResponse for streaming.

Implement chunked uploads: split file into parts client-side and reassemble server-side.

Consider WCF streaming for direct streamed calls to services.

Example: Simple HttpWebRequest upload (outline)

Create HttpWebRequest to POST to handler.

Get request stream asynchronously, write file bytes in chunks, call GetResponse.

(For brevity, code omitted; follow similar patterns as WebClient but managing streams directly.)

9. Testing and debugging

Test with various file sizes and types.

Use Fiddler or browser dev tools to inspect requests.

Log server-side exceptions.

Ensure content-length and boundaries are correct in multipart body.

10. Wrap-up

This guide demonstrated creating a Silverlight UI to pick a file, validate it, upload via multipart/form-data to an ASP.NET endpoint, and handle progress and errors. For production, prefer server-side validation, HTTPS, and handling large files via streaming or chunking.

If you want, I can provide a full sample project (client and server) with HttpWebRequest chunked upload and resume support.

Troubleshooting Silverlight File Upload Errors and Fixes

How to Implement Silverlight File Upload: Step-by-Step Guide

Prerequisites

Overview of the approach

1. Create the Silverlight project and host

2. Build the UI (XAML)

3. Let users pick files (OpenFileDialog)

4. Client-side validation

5. Uploading the file from Silverlight

6. Server-side: Receive and save the file (ASP.NET handler)

7. Security and robustness tips

8. Large files and advanced scenarios

Example: Simple HttpWebRequest upload (outline)

9. Testing and debugging

10. Wrap-up

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