securityException in Silverlight: dialogs must be user initiated

Question

I'm trying to create a Silverlight application that downloads a file accessed by a URL. I tried using WCF, but now I'm attempting to do it with Webclient. When I try using this sample code, I'm getting a securityException error that says "Dialogs must be user initiated." Can someone please explain what I'm doing wrong? Thanks.

using System;
using System.IO;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;

namespace SilverlightApplication1
{
    public partial class MainPage : UserControl
    {
        #region Constructors
        public MainPage()
        {
            InitializeComponent();

           // SaveFileDialog sfd = new SaveFileDialog();

        }
        #endregion

        #region Handlers

        void webClient_OpenReadCompleted(object sender, OpenReadCompletedEventArgs e)
        {
            SaveFileDialog sfd = new SaveFileDialog();
            if ((bool)sfd.ShowDialog())
            {
                StreamReader sr = new StreamReader(e.Result);
                string str = sr.ReadToEnd();

                StreamWriter sw = new StreamWriter(sfd.OpenFile());
                sw.Write(str);
           }
        }

        private void download_Click_1(object sender, RoutedEventArgs e)
        {
            WebClient webClient = new WebClient();
            webClient.OpenReadCompleted += new OpenReadCompletedEventHandler(webClient_OpenReadCompleted);
            webClient.OpenReadAsync(new Uri("http://www.productimageswebsite.com/images/stock_jpgs/34891.jpg", UriKind.Absolute));
        }
        #endregion
    }
}

possible duplicate of ["Dialogs must be user-initiated." with SaveFileDialog in Silverlight 3](http://stackoverflow.com/questions/1355078/dialogs-must-be-user-initiated-with-savefiledialog-in-silverlight-3) — CodeNaked, Aug 05 '11 at 16:05
I agree this to be a duplicate but the answers to the previous are unsatisfactory (IMO) and the question is a little old. I'll answer here. — AnthonyWJones, Aug 05 '11 at 21:20

score 1 · Accepted Answer · edited Aug 06 '11 at 10:24

The basic problem as the answers to the older questions point out is that the OpenReadCompleted event occurs asynchronously with the button click. There is no way for silverlight be be sure that code execting in the event handler is a result of a user action.

What is needed to turn things around, get the user to pick the save destination before invoking the download. Here is a button click event that handles the lot:-

private void Button_Click(object sender, RoutedEventArgs e)
{
    SaveFileDialog sfd = new SaveFileDialog();
    if (sfd.ShowDialog() ?? false)
    {

        WebClient client = new WebClient();
        client.OpenReadCompleted += (s, args) =>
        {
            using (Stream output = sfd.OpenFile())
            {
                args.Result.CopyTo(output);
                output.Flush();
            }
        };
        client.OpenReadAsync(new Uri("http://www.productimageswebsite.com/images/stock_jpgs/34891.jpg", UriKind.Absolute));
    }
}

BTW had you been successfull your use of StreamReader / StreamWriter may well have messed things up, these are for reading and writing text. In this case a simple call to CopyTo does the trick.

Thanks for the help, any clue why I'm getting this error? Unhandled Error in Silverlight Application An exception occurred during the operation, making the result invalid. Check InnerException for exception details. at System.ComponentModel.AsyncCompletedEventArgs.RaiseExceptionIfNecessary() at System.Net.OpenReadCompletedEventArgs.get_Result() at SilverlightApplication1.MainPage.<>c__DisplayClass2.b__0(Object s, OpenReadCompletedEventArgs args) at System.Net.WebClient.OnOpenReadCompleted(OpenReadCompletedEventArgs e) at System.Net.WebClient.... — Vinny, Aug 08 '11 at 13:06
@Vinny: Doesn't sound like that is related directly to this question and its really hard reading technical details in a comment. Put together a new question containing all the relevant details. — AnthonyWJones, Aug 09 '11 at 08:02

securityException in Silverlight: dialogs must be user initiated

1 Answers1