Pause execution of a method without locking GUI. C#

Question

I'm working on a card game in C# for a project on my Intro to OOP paper and have got the game working now but am adding "flair" to the GUI.

Currently cards are dealt and appear on the UI instantaneously. I want to have to program pause for a moment after dealing a card before it deals the next.

When a game is started the following code runs to populate the PictureBoxes that represent them (will be a loop eventually):

        cardImage1.Image = playDeck.deal().show();
        cardImage2.Image = playDeck.deal().show();
        cardImage3.Image = playDeck.deal().show();
        cardImage4.Image = playDeck.deal().show();
        cardImage5.Image = playDeck.deal().show();
        ...

I have tries using System.Threading.Thread.Sleep(100); between each deal().show() and also inside each of those methods but all it achieves is locking up my GUI until all of the sleeps have processed then display all of the cards at once.

I have also tried using a combination of a timer and while loop but it resulted in the same effect.

What would be the best way of achieving the desired result?

Answer 1

The problem is that any code that you run on the UI will block the UI and freeze the program. When your code is running (even if it's running Thread.Sleep), messages (such as Paint or Click) sent to the UI will not be processed (until control returns to the message loop when you exit your event handler), causing it to freeze.

The best way to do this is to run on a background thread, and then Invoke to the UI thread between sleeps, like this:

//From the UI thread,
ThreadPool.QueueUserWorkItem(delegate {
    //This code runs on a backround thread.
    //It will not block the UI.
    //However, you can't manipulate the UI from here.
    //Instead, call Invoke.
    Invoke(new Action(delegate { cardImage1.Image = playDeck.deal().show(); }));
    Thread.Sleep(100);

    Invoke(new Action(delegate { cardImage2.Image = playDeck.deal().show(); }));
    Thread.Sleep(100);

    Invoke(new Action(delegate { cardImage3.Image = playDeck.deal().show(); }));
    Thread.Sleep(100);

    //etc...
});
//The UI thread will continue while the delegate runs in the background.

---

Alternatively, you could make a timer and show each image in the next timer tick. If you use a timer, all you should do at the beginning is start the timer; don't wait for it or you'll introduce the same problem.

Answer 2

I would try puting the code that deals the deck ( and calls Thread.Sleep) in another thread.

Answer 3

The cheap way out would be to loop with calls to Application.DoEvents() but a better alternative would be to set a System.Windows.Forms.Timer which you would stop after the first time it elapses. In either case you'll need some indicator to tell your UI event handlers to ignore input. You could even just use the timer.Enabled property for this purpose if it's simple enough.

Answer 4

Normally I'd simply recommend a function like this to perform a pause while allowing the UI to be interactive.

  private void InteractivePause(TimeSpan length)
  {
     DateTime start = DateTime.Now;
     TimeSpan restTime = new TimeSpan(200000); // 20 milliseconds
     while(true)
     {
        System.Windows.Forms.Application.DoEvents();
        TimeSpan remainingTime = start.Add(length).Subtract(DateTime.Now);
        if (remainingTime > restTime)
        {
           System.Diagnostics.Debug.WriteLine(string.Format("1: {0}", remainingTime));
           // Wait an insignificant amount of time so that the
           // CPU usage doesn't hit the roof while we wait.
           System.Threading.Thread.Sleep(restTime);
        }
        else
        {
           System.Diagnostics.Debug.WriteLine(string.Format("2: {0}", remainingTime));
           if (remainingTime.Ticks > 0)
              System.Threading.Thread.Sleep(remainingTime);
           break;
        }
     }
  }

But there seems to be some complication in using such a solution when it is called from within an event handler such as a button click. I think the system wants the button click event handler to return before it will continue processing other events because if I try to click again while the event handler is still running, the button depresses again even though I'm trying to drag the form and not click on the button.

So here's my alternative. Add a timer to the form and create a dealer class to handle dealing with cards by interacting with that timer. Set the Interval property of the timer to match the interval at which you want cards to be dealt. Here's my sample code.

public partial class Form1 : Form
{

  CardDealer dealer;

  public Form1()
  {
     InitializeComponent();
     dealer = new CardDealer(timer1);
  }

  private void button1_Click(object sender, EventArgs e)
  {
     dealer.QueueCard(img1, cardImage1);
     dealer.QueueCard(img2, cardImage2);
     dealer.QueueCard(img3, cardImage1);
  }
}

class CardDealer
{
  // A queue of pairs in which the first value represents
  // the slot where the card will go, and the second is
  // a reference to the image that will appear there.
  Queue<KeyValuePair<Label, Image>> cardsToDeal;
  System.Windows.Forms.Timer dealTimer;

  public CardDealer(System.Windows.Forms.Timer dealTimer)
  {
     cardsToDeal = new Queue<KeyValuePair<Label, Image>>();
     dealTimer.Tick += new EventHandler(dealTimer_Tick);
     this.dealTimer = dealTimer;
  }

  void dealTimer_Tick(object sender, EventArgs e)
  {
     KeyValuePair<Label, Image> cardInfo = cardInfo = cardsToDeal.Dequeue();
     cardInfo.Key.Image = cardInfo.Value;
     if (cardsToDeal.Count <= 0)
        dealTimer.Enabled = false;
  }

  public void QueueCard(Label slot, Image card)
  {
     cardsToDeal.Enqueue(new KeyValuePair<Label, Image>(slot, card));
     dealTimer.Enabled = true;
  }
}