Application Dispatcher doesn't update and doesn't give errors

Question

I have an application and i need to download a lot of files. Actually to download i use this code:

System.Net.ServicePointManager.DefaultConnectionLimit = Int32.Parse(Properties.Settings.Default["download_threads"].ToString());
var block = new System.Threading.Tasks.Dataflow.ActionBlock<string>(async url =>
{
    await DownloadLibraries(url);
}, new ExecutionDataflowBlockOptions { MaxDegreeOfParallelism = Int32.Parse(Properties.Settings.Default["download_threads"].ToString()) });

foreach (var url in urls)
{
    block.Post(url);
}

block.Complete();
await block.Completion;

It works just fine, it downloads everything i need with parallel downloads. Inside the DownloadLibraries method i want to update a label. Here is the code:

Application.Current.Dispatcher.Invoke(new Action(() =>
{
    string urlnum = this.filesToDownload.Content.ToString().Split('/')[0];
    if (Array.IndexOf(urls, url) > Int32.Parse(urlnum))
        this.filesToDownload.Content = Array.IndexOf(urls, url) + "/" + count.ToString();

    if ((Array.IndexOf(urls, url) * 100) > totalProgress.Value)
        this.totalProgress.Value = (Array.IndexOf(urls, url) * 100) / count;
}));

It doesn't give me any error but it doesn't update the label either. If i do Console.Write((Array.IndexOf(urls, url) * 100) / count); it works fine, i can see in the output space in visual studio the percentage going up but the label doesn't update at all. What could be the problem?

I tried it with a similar test program and for me your solution worked perfectly. Could you try setting MaxDegreeOfParallelism to 1? — Istvan Reiter, Feb 07 '16 at 14:52

score 0 · Accepted Answer · answered Feb 07 '16 at 12:26

You should call .Invoke() on the element's Dispatcher:

this.filesToDownload.Dispatcher.Invoke(new Action(() =>
{
    string urlnum = this.filesToDownload.Content.ToString().Split('/')[0];
    if (Array.IndexOf(urls, url) > Int32.Parse(urlnum))
        this.filesToDownload.Content = Array.IndexOf(urls, url) + "/" + count.ToString();

    if ((Array.IndexOf(urls, url) * 100) > totalProgress.Value)
        this.totalProgress.Value = (Array.IndexOf(urls, url) * 100) / count;
}));

@giogiowefj does it being run? Try placing a breakpoint inside the Action. — AgentFire, Feb 07 '16 at 15:23

Application Dispatcher doesn't update and doesn't give errors

1 Answers1