Question

I have a WPF user control called TimerUserControl where contains a timer. And I have another user control where show questions, this one has a NextQuestion function.

The timer has 2 minutes like an interval, and I’d like to invoke the NextQuestion function when it has done. I think I have to use delegates, but I’m not sure.

UPDATE 1:

public partial class TimeUserControl : UserControl
{
    public int _totalSeconds;
    public int _secondsRemaining;
    public DispatcherTimer timerSecondsLeft;

    public TimeUserControl()
    {
        InitializeComponent();

        timerSecondsLeft = new DispatcherTimer();
        timerSecondsLeft.Tick += new EventHandler(timerSecondsLeft_Tick);
        timerSecondsLeft.Interval = new TimeSpan(0, 0, 1);
    }

    public bool TimesUp
    {
        get;
        set;
    }

    public void SetSeconds(int seconds)
    {
        timerSecondsLeft.Stop();

        if (seconds == 0)
        {
            TimeTextBlock.Text = "There's no time! Hurray";
        }
        else
        {
            _totalSeconds = seconds;
            _secondsRemaining = seconds;

            TimeTextBlock.Text = string.Format("It remains {0} seconds. Don't take long!", _totalSeconds);
            timerSecondsLeft.Start();
        }
    }

    public void timerSecondsLeft_Tick(object sender, EventArgs e)
    {
        _secondsRemaining--;

        if (_secondsRemaining <= 0)
        {
            timerSecondsLeft.Stop();

            TimesUp = true;
            TimeTextBlock.Text = "Time's up. Press Enter to next problem.";

            // HERE WILL INVOKE NEXTQUESTION FUNCTION
        }
        else
        {
            TimeTextBlock.Text = string.Format("It remains {0} seconds. Don't take long!", _secondsRemaining);
        }
    }
}

Look in the code, the comment is this possible ussing delegates?

Answer 1

So you need to do a few things. You have to add some code to you’re user control.

// Declare this outside your usercontrol class
public delegate void TimerExpiredEventHandler(object sender, EventArgs e);

This is what needs to be added to your code for the user control.

public partial class TimerUserControl : UserControl
{
    public event TimerExpiredEventHandler Expired;

    public void OnExpired(EventArgs e)
    {
        if (Expired != null)
            Expired(this, e);
    }

public void timerSecondsLeft_Tick(object sender, EventArgs e)
{
    _secondsRemaining--;

    if (_secondsRemaining <= 0)
    {
        timerSecondsLeft.Stop();

        TimesUp = true;
        TimeTextBlock.Text = "Time's up. Press Enter to next problem.";

        // Fire the event here.
        OnExpired(EventArgs.Empty);
    }
    else
    {
        TimeTextBlock.Text = string.Format("It remains {0} seconds. Don't take long!", _secondsRemaining);
    }
}

}

Now you need to subscribe to this event inside whatever is calling this usercontrol in the first place.

public partial class ParentForm : Form
{
    private void ParentForm_Load(object sender, EventArgs e)
    {
         var timer = new TimerUserControl();
         //Subscribe to the expired event that we defined above.
         timer.Expired += new EventArgs(Timer_Expired);
    }

    public void Timer_Expired(object sender, EventArgs e)
    {
        //Handle the timer expiring here. Sounds like you are calling another function, so do that here.
    }
}