UIActivityIndicator is not working correctly Xamarin IOS - ios

Question

I am including UIActivityIndicator in my UIViewController.
I need to bring a file from FTP using.
I have a button on my ViewController, upon clicking that button, download will start. I put a UIActivityIndicator (aiReceive) on my ViewController, That is appearing in stopped state on my view controller, but only animate upon completing file download.
I am making a iPad App in Xamarin IOS.
I added the Async Method, but i am getting the below error now.
The await operator can only be used when its containing lambda expression is marked with the async modifier
public partial class FirstViewController : UIViewController
{
public override void ViewDidLoad()
{
base.ViewDidLoad();
btnReceiveData.TouchUpInside += (object sender, EventArgs e) =>
{
//BTProgressHUD.Show("Receiving Data..."); --> This Component is also not working,
aiReceive.StartAnimating();
await GetFileAsync());
BTProgressHUD.Dismiss();
};
}
async Task GetFileAsync()
{
using (var client = new HttpClient())
{
try
{
aiReceive.StartAnimating(); /* --> Inimation is not starting at this point. Animation Start After Downloading file, download takes time, i want to show animation in the mean while.*/
using (WebClient ftpclient = new WebClient())
{
try
{
ftpclient.Credentials = new System.Net.NetworkCredential("UserName", "Password");
string sourceFilePath = #"ftp://ftp.google.com/FileName.pdf";
var FileDownloadStart = UIAlertController.Create("Info", "Data file received.", UIAlertControllerStyle.Alert);
FileDownloadStart.AddAction(UIAlertAction.Create("Ok", UIAlertActionStyle.Default, null));
UIApplication.SharedApplication.KeyWindow.RootViewController.PresentViewController(FileDownloadStart, true, null);
//Downloading file from FTP.
ftpclient.DownloadFile(sourceFilePath, "C:\");
var FileDownloadAlert = UIAlertController.Create("Info", "Data file received.", UIAlertControllerStyle.Alert);
FileDownloadAlert.AddAction(UIAlertAction.Create("Ok", UIAlertActionStyle.Default, null));
UIApplication.SharedApplication.KeyWindow.RootViewController.PresentViewController(FileDownloadAlert, true, null);
}
catch (Exception ex)
{
File.Delete(EpazzDirectory + AuditorId.ToString());
var ExceptionAlert = UIAlertController.Create("Exception", ex.Message, UIAlertControllerStyle.Alert);
ExceptionAlert.AddAction(UIAlertAction.Create("Ok", UIAlertActionStyle.Default, null));
UIApplication.SharedApplication.KeyWindow.RootViewController.PresentViewController(ExceptionAlert, true, null);
}
}
}
}
}
}

Answer 1

You're blocking the UI thread, and that will prevent the changes you want to make to the UI from taking effect (in this case UIActivityIndicator spinning animation).
The best way to do this is using async/await like:
aiReceive.StartAnimating();
await YourFTPRequestAsync();
aiReceive.StopAnimating();
Here are official MSDN documentation on async\await and a sample driven hint on how it works