C# - A simple way to call a method async? - events

Question

i am developing a c# user-control # work. the control just loads some infos & data and displays it.
now i want to provide the user of the control with an option to load the data asynchron .. smth like this:
Cntrl.LoadSmthAsync(..)
Cntrl.LoadSmthComplete //EventHandler to give feedback if the Load was successfull.
i decided to make the Download function Async and provide return values throu EventHandlers. but that code got rather complicated .. after all.
here some code to understand what the control should do:
public byte[] LoadByPos(int pos)
{
string url = Pos2Url(pos);
// update gui
this.textBox1.Text = url;
byte[] res = LoadByUrl(url);
// update gui
this.textBox2.Text = BytesToString(res);
return res;
}
public byte[] LoadByUrl(string url)
{
return Download(url);
}
//primary problem: download function
private byte[] Download(string url)
{
System.Threading.Thread.Sleep(1000 * 30);
return StringToBytes(url);
}
//secondary problem: an other function
private string Pos2Url(int pos)
{
System.Threading.Thread.Sleep(1000 * 5);
return pos.ToString();
}
// LoadByPosAsync
public delegate void LoadByPosDoneHandler(Object sender, byte[] e);
public event LoadByPosDoneHandler LoadByPosDone;
public void LoadByPosAsync(int pos)
{
string url = Pos2Url(pos);
// update gui
this.textBox1.Text = url;
LoadByUrlDone += new LoadByUrlDoneHandler(LoadByPosAsync_LoadByUrlDone);
LoadByUrlAsync(url);
}
public void LoadByPosAsync_LoadByUrlDone(object sender, byte[] e)
{
// update gui
this.textBox2.Text = BytesToString(e);
LoadByUrlDone = null;
LoadByPosDone(sender, e);
}
//LoadByUrlAsync
public delegate void LoadByUrlDoneHandler(Object sender, byte[] e);
public event LoadByUrlDoneHandler LoadByUrlDone;
public void LoadByUrlAsync(string url)
{
DownloadDone += new DownloadDoneHandler(LoadByUrlAsync_DownloadDone);
DownloadAsync(url);
}
private void LoadByUrlAsync_DownloadDone(object sender, byte[] e)
{
LoadByUrlDone(sender, e);
}
//DownloadAsync
private delegate void DownloadDoneHandler(Object sender, byte[] e);
private event DownloadDoneHandler DownloadDone;
private void DownloadAsync(string url)
{
BackgroundWorker bw_DownloadAsync = new BackgroundWorker();
bw_DownloadAsync.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bw_DownloadAsync_RunWorkerCompleted);
bw_DownloadAsync.DoWork += new DoWorkEventHandler(bw_DownloadAsync_DoWork);
bw_DownloadAsync.RunWorkerAsync(url);
}
void bw_DownloadAsync_DoWork(object sender, DoWorkEventArgs e)
{
byte[] res = Download((string)e.Argument);
e.Result = res;
}
void bw_DownloadAsync_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
DownloadDone(sender, (byte[])e.Result);
}
is there an easier way to accomplish what i am intending to do ?
thx in advance

Answer 1

Is there an easier way to accomplish what I am intending to do?
There's the implementation side separately, but if you're using .NET 4 I would strongly advise you not to use this model for asynchrony. Rather than using event handlers, I'd encourage you to use Task<T>. You can use TaskCompletionSource to create the task if you don't have any inherent support for it, and it means your API will be much easier to use in C# 5, due to the async/await support. At that point, your UI-thread method would look like this:
public async Task<byte[]> LoadByPos(int pos)
{
string url = await Pos2UrlAsync(pos);
// update gui
this.textBox1.Text = url;
byte[] res = await LoadByUrlAsync(url);
// update gui
this.textBox2.Text = BytesToString(res);
return res;
}
The asynchrony will simply flow through your code naturally.