// Very old-school implementations use an IAsyncResult by Jeffrey Richter from an old MSDN article:
// https://docs.microsoft.com/en-us/archive/msdn-magazine/2007/march/implementing-the-clr-asynchronous-programming-model
// This example code uses the much simpler Task/TaskCompletionSource approach introduced in .NET 4.0.
public IAsyncResult BeginDownloadAndSave(AsyncCallback callback, object state)
{
var tcs = new TaskCompletionSource <object>(state);
_downloadFromInternet.BeginDownload(ar =>
{
string data;
try
{
data = _downloadFromInternet.EndDownload(ar);
}
catch (Exception exception)
{
tcs.TrySetException(exception);
return;
}
_saveToDatabase.BeginSave(data, ar =>
{
try
{
_saveToDatabase.EndSave(ar);
}
catch (Exception exception)
{
tcs.TrySetException(exception);
return;
}
tcs.TrySetResult(null);
}, null);
}, null);
return(tcs.Task);
}
public IAsyncResult BeginDownloadAndSave(AsyncCallback callback, object userState)
{
var localState = new State(userState);
_downloadFromInternet1.BeginDownload(Download1Callback, localState);
_downloadFromInternet2.BeginDownload(Download2Callback, localState);
return(localState.TaskCompletionSource.Task);
}