Wait untill an event raised and then continue code

Question

I developed an application with Windows Forms using C#(visual studio 2010). This application should connect to a server and get data, then process that data.

public partial class Form1 : Form
{
    public string Result = "";

    MyServer server = new MyServer();

    public Form1()
    {
        InitializeComponent();

        server.RecieveMessage += new MyServer.RecieveMessageEventHandler(server_RecieveMessage);
    }

    void server_RecieveMessage(object sender, string message)
    {
        Result = message;
    }


    public string SendCommand(string Command)
    {


        server.Send(Command);

        //wait untill RecieveMessage event raised


        //process Data is recieved

        server.Send(AnotherCommand);

        //wait untill RecieveMessage event raised


        //process Data is recieved

        ....

            //till i get what i want
        return Result;
    }

So I want to wait after server.Send(Message) until I get the result on event. Sometimes it takes 4 to 5 seconds until I get the result. What do I have to do?

Answer 1

One possible way of doing this asynchronously is using TaskCompletionSource<T>. It could look like this:

public async Task<string> SendMessageAsync(string message)
{
    var tcs = new TaskCompletionSource<string>();

    ReceiveMessangeEventHandler eventHandler = null;
    eventHandler = (sender, returnedMessage) =>
    {
        RecieveMessage -= eventHandler;
        tcs.SetResult(returnedMessage);
    }

    RecieveMessage += eventHandler;

    Send(message);
    return tcs.Task;
}

Now, when you want to call it and asynchronously wait for the result, you do this:

public async void SomeEventHandler(object sender, EventArgs e)
{
    var response = await server.SendMessageAsync("HelloWorld");
    // Do stuff with response here
}

SendMessageAsync will asynchronously yield control back to the caller until the message is received. Then, once it resumes on the next line, you can alter the response.