How do I wait for something to finish in C#?

Question

 private void Download_Click(object sender, EventArgs e)
        {
            label1.Text = "Downloading...";
            WebClient wc = new WebClient();
            string program = "Program";
            string link = "https://linkhere.com";
            string download = wc.DownloadString(link);
            string path = "Program\\" + program + ".zip";
            string patch = "Program";
            Directory.CreateDirectory(patch);
            wc.DownloadFile(download, path);
            label1.Text = "Downloaded!";
        }

I want to make the label1.Text = "Downloaded!"; to happen after it downloads the program.

_"I want to make the label1.Text = "Downloaded!"; to happen after it downloads the program."_ - thats exactly what should happen as you've chosen the synchronous version of that download method. — Jamiec, Jan 06 '22 at 11:37
welcome to StackOverflow. Please edit you post and try to be more precise on the problem: what is the exact difference between the expected and actual outcome of your code. Up to now we don't really see the problem — Mong Zhu, Jan 06 '22 at 11:40

score 2 · Answer 1 · answered Jan 06 '22 at 11:40

2

You need to make the download asynchronous to prevent the deadlock.

private async void Download_Click(object sender, EventArgs e)
{
    label1.Text = "Downloading...";
    WebClient wc = new WebClient();
    string program = "Program";
    string link = "https://linkhere.com";
    string download = wc.DownloadString(link);
    string path = "Program\\" + program + ".zip";
    string patch = "Program";
    Directory.CreateDirectory(patch);
    await wc.DownloadFileAsync(download, path);
    label1.Text = "Downloaded!";
}

answered Jan 06 '22 at 11:40

Yuriy Faktorovich

67,283
14
105
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2

`DownloadFileAsync` != `DownloadFileTaskAsync` (it's not awaitable) -- WebClient really needs to be disposed of. – Jimi Jan 06 '22 at 19:35
@Jimi it's pretty standard practice to have an instance of WebClient running for the lifetime of the class. What version of .net are you on? – Yuriy Faktorovich Jan 06 '22 at 20:02
1

That's a local object. -- The .Net version is not factor. – Jimi Jan 07 '22 at 00:15
2

The most important thing is that `DownloadFileAsync` is not awaitable, it's event-driven. – Jimi Jan 07 '22 at 00:31
@Jimi you're doing something wrong, it is awaitable – Yuriy Faktorovich Jan 07 '22 at 02:42
2

`public void DownloadFileAsync (Uri address, string fileName);` -- declared `void`: how do you await `void`? Doesn't matter, it's not awaitable, as mentioned it's event-driven. The awaitable method is the `DownloadFileTaskAsync` counterpart (which of course returns a `Task`). – Jimi Jan 07 '22 at 06:03
1

@dr.null It's not about awaiting an async call in an `async void` method, it's DownloadFileAsync that is not awaitable. It's an [AsyncOperation](https://referencesource.microsoft.com/#System/compmod/system/componentmodel/AsyncOperation.cs,e6f378e28a257e11), i.e., it's *asynchronous* in the *old* terms, driven by events, it cannot be handled as a Task, simply because it's not. – Jimi Jan 07 '22 at 15:42
@Jimi aha, got it. Thank you Jim. – dr.null Jan 07 '22 at 15:54

score 0 · Answer 2 · answered Jan 06 '22 at 11:41

0

The DownloadFile docs say "This method blocks while downloading the resource", so I'm not sure what could be different about your situation, or if there even is a problem.

I suspect that you never see "Downloading..." because the UI does not update in between the two label1.Text update calls. Adding Application.DoEvents() after the first .Text update may help.

answered Jan 06 '22 at 11:41

Peter B

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As for the `Application.DoEvents`, please read [this](https://stackoverflow.com/a/5183623/14171304). – dr.null Jan 06 '22 at 12:13

score 0 · Answer 3 · answered Jan 06 '22 at 12:03

0

Please Use tasks and events to handle the situation.

answered Jan 06 '22 at 12:03

Pran

1
1

As it’s currently written, your answer is unclear. Please [edit] to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers [in the help center](/help/how-to-answer). – Community Jan 06 '22 at 12:06

score 0 · Answer 4 · answered Jan 06 '22 at 13:06

You can modify your download to with this as reference.

    public static async Task Main()
    {
        Task task1 = new Task(() => ActionToWork1());
        Task task2 = new Task(() => ActionToWork2());
        
        task1.Start();
        task2.Start();
        await Task.WhenAll(task1, task2);
        Console.WriteLine("All task done.");    
    }
    
    private static void ActionToWork1(){
        Console.WriteLine("Working on Task 1"); 
    }
    
    private static void ActionToWork2(){
        Console.WriteLine("Working on Task 2"); 
    }

How do I wait for something to finish in C#?

4 Answers4

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