Unity C# - Execute async task within a Coroutine and wait for it to finish

Question

I'm completely new to Unity development and I'm trying to integrate an asynchronous functionality into an existing Coroutine but I have faced several issues so far. My issues:

1. The Unity app completely freezes, probably because it was blocked by a thread. I implemented this code in traditional C# (console app) without having any issues.(Fixed now in Unity after some modifications)
2. The download task begins but it never finishes . This happens only when I run it as APK. On Unity debugging on PC works fine.

My code:

public void Validate()
{
     StartCoroutine(DoWork());
}


 private IEnumerator DoWork()
 {
    bool success;
    //Perform some calculations here
    ..
    ..
    success = true;
    //
    yield return new WaitForSeconds(3);
    if(success){
        GetInfo(_files);
    }
 
 }
 
 async void GetInfo(List<string> files)
 {
     await StartDownload(files);
     
     //After completing the download operation, perform some other actions in the background
     ...
     ...
     //
     
     //When done, change the active status of specific game objects
 }
 
 
 public async Task StartDownload(List<string> files){
    
    var t1 = GetFileSizesAsync(files);
    var t2 = DownloadFilesAsync(files);
    
    await Task.WhenAll(t1, t2);
 
 }
 
  public async Task GetFileSizesAsync(List<string> urls)
  {
        foreach (var url in urls)
           GetFileSize(url);
           
        txtSize.text = totalSizeMb +"MB";
  }
  
   private void GetFileSize(string url)
   {
         var uri = new Uri(url);
        var webRequest = HttpWebRequest.Create(uri);
        webRequest.Method = "GET";
        try
        {
            var webResponse = webRequest.GetResponse();
            var fileSize = webResponse.Headers.Get("Content-Length");
            var fileSizeInMegaByte = Math.Round(Convert.ToDouble(fileSize) / 1024.0 / 1024.0, 2);
            totalSizeMb = totalSizeMb + fileSizeInMegaByte;
          
        }
        catch (Exception ex)
        {

        }
        finally
        {
            webRequest.Abort();
        }
   }
   
   
   public async Task<List<string>> DownloadFilesAsync(List<string> urls)
    {
        var result = new List<string>();
        
        foreach (var url in urls)
           var download = await DownloadFile(url);
            if(download)
                result.Add(url);
            
        return response;
    }
    
    private async Task<bool> DownloadFile(string url)
    {
        WebClient webClient = new WebClient();
        var uri = new Uri(url);
        var saveHere = "C:\\...";
        try
        {
            await webClient.DownloadFileTaskAsync(uri, saveHere);
            return true;
        }
        catch (Exception ex)
        {
            return false;
        }
    }

Can you tell me what I'm doing wrong here? I've tried several ways but couldn't manage to find a proper solution.

Thank you!

Answer 1

I would rather make it

async Task GetInfo(List<string> files){ ... }

And then in your Coroutine do

var t = Task.Run(async () => await GetInfo(files));

while(!t.IsCompleted)
{
    yield return null;
}

// Or also
//yield return new WaitUntil(() => t.IsCompleted);

if(!t.IsCompletedSuccesfully)
{
    Debug.LogError("Task failed or canceled!");
    yield break;
}

---

Note however:

When done, change the active status of specific game objects

This can't be done async! It has to happen in the Unity main thread! Therefore you would probably rather return something from your GetInfo task and activate the objects in the Coroutine when done.

after the loop and yielding you could then access the return value via

var result = t.Result;

---

Your web requests are currently totally redundant! You start get requests only to check how big the received content is but immediately throw away that received content ... then you start a second request to actually download the files (again).

In general I would recommend to rather use a UnityWebRequest.Get you can directly yield in the Coroutine in combination with a DownloadHandlerFile which allows you to directly download the content into a local file instead of into runtime memory.

---

Also

var saveHere = "C:\\...";

is hopefully not what you are trying to use as path on Android ;)

Answer 2

First of all. The freezing is definitely being done by the IEneumerator as I don't see a yield statement. What's a yield statement? Uhhhh...Google it. lel

Second of all. Wouldn't a normal void work just fine?

Third of all. I don't know much about async's since I'm pretty new to them but I'm fairly certain you don't need them for:

Task GetFileSizesAsync(List urls)

AND

async Task<List> DownloadFilesAsync(List urls)

I may be wrong tho.