Wait inside method until event is captured

Question

I have this issue with a method in C#. I made a method that calls a function from a dll its called Phone.GetLampMode(); Now Phone.GetLampMode doesnt return anything. The data gets returned in a event the 'onGetLampModeResponse' event. Is there a way i can wait in my method until i get the data from the onGetLampModeResponse event?

public bool checkLamp(int iLamp)
{
    Phone.ButtonIDConstants btn = new Phone.ButtonIDConstants();
    btn = Phone.ButtonIDConstants.BUTTON_1;
    btn += iLamp;
    Phone.GetLampMode(btn, null);

    return true;
}

private void Phone_OnGetLampModeResponse(object sender, Phone.GetLampModeResponseArgs e)
{
    var test = e.getLampModeList[0].getLampMode.ToString();    
}

Answer 1

One solution is to use AutoResetEvent:

public bool checkLamp(int iLamp)
{
    Phone.ButtonIDConstants btn = new Phone.ButtonIDConstants();
    btn = Phone.ButtonIDConstants.BUTTON_1;
    btn += iLamp;

    AutoResetEvent waitHandle = new AutoResetEvent(false); 

    // Pass waitHandle as user state
    Phone.GetLampMode(btn, waitHandle);

    // Wait for event completion
    waitHandle.WaitOne();

    return true;
}

private void Phone_OnGetLampModeResponse(object sender, Phone.GetLampModeResponseArgs e)
{
    var test = e.getLampModeList[0].getLampMode.ToString();

    // Event handler completed
    // I guess there is some UserState property in the GetLampModeResponseArgs class
    ((AutoResetEvent)e.UserState).Set();
}

NOTE: Ad you're using Phone as a static class/variable, one can think you're developing on Windows Phone... If it is the case, do note that the whole concept of WP and async programming is to not lock the UI thread in a such way.

Answer 2

You can wrap the handler in an asynchronous method, which should look something like this (untested):

public async Task<bool> checkLamp(int iLamp)
{
    Phone.ButtonIDConstants btn = new Phone.ButtonIDConstants();
    btn = Phone.ButtonIDConstants.BUTTON_1;
    btn += iLamp;

    var tcs = new TaskCompletionSource<bool>();
    var handler = (sender, e) => {
        Phone.OnGetLampModeResponse -= handler;
        var test = e.getLampModeList[0].getLampMode.ToString();
        tcs.SetResult(true);
    };
    Phone.OnGetLampModeResponse += handler;

    Phone.GetLampMode(btn, null);

    return tcs.Task;
}

In your calling method, you would write:

var returnValue = await checkLamp(iLamp);

This has the advantage that your user interface does not block while the process is waiting for the response.

Here's a blog entry on this issue. Note that Framework 4.5 is required.

• http://blogs.msdn.com/b/lucian/archive/2012/11/28/how-to-await-a-button-click.aspx