It would appear I’m going to start pumping out little “lessons learned” articles over the next few weeks, as I’ve learned an absolute TON from building my King Poker app. Today’s lesson is about capturing keystrokes.
Many of you have probably done this before: you want to recognize a specific key that has been pressed when a user is entering something into a TextBox. Maybe you want to take action when they press the Enter key, for example. This is generally simple enough, you just set up a KeyDown (or KeyUp, depending on your needs) event on the TextBox in question, and then just check every time the event fires until you find the key you’re looking for.
That’s not what I wanted to do.
To give you some context, here’s a screenshot of my app:
For the cards in question, I want to hold the three Queens, and then re-deal, hoping to get the 4th Queen, or maybe one of the Wild Deuces. (If I’m very lucky, BOTH!)
As the game currently stands, it is designed for use on a touch screen or with a mouse. Clicking/tapping on a card will mark it as “HELD,” and won’t replace it when you click the “DEAL” button. But you have to actually move your fingers or mouse to each card to mark them. For speed players, they’d prefer physical buttons that can be pressed over having to touch a screen.
This is where my key capture needs come in.
I don’t have a control that I can just drop a KeyDown event on. I want to be able to monitor keystrokes at all times. For this, we can simply wire up an event in the code-behind file, and capture it there. Here’s what it looks like:
protected override void OnNavigatedTo(NavigationEventArgs e)
{
Window.Current.CoreWindow.KeyDown += CoreWindow_KeyDown;
}
void CoreWindow_KeyDown(Windows.UI.Core.CoreWindow sender, Windows.UI.Core.KeyEventArgs args)
{
switch (args.VirtualKey)
{
case Windows.System.VirtualKey.Number1:
if (HoldRound) HoldCard(Card0);
else SetBet(1);
break;
case Windows.System.VirtualKey.Number2:
HoldCard(Card1);
break;
case Windows.System.VirtualKey.Number3:
HoldCard(Card2);
break;
case Windows.System.VirtualKey.Number4:
HoldCard(Card3);
break;
case Windows.System.VirtualKey.Number5:
if (HoldRound) HoldCard(Card4);
else SetBet(5);
break;
case Windows.System.VirtualKey.Space:
Deal();
break;
}
}
protected override void OnNavigatingFrom(NavigatingCancelEventArgs e)
{
Window.Current.CoreWindow.KeyDown -= CoreWindow_KeyDown;
}
As you can see above, I subscribe to the Window.Current.CoreWindow.KeyDown event, which fires before anything else gets access to the key event. This is also a great way to capture keystrokes before they get to your TextBox controls, etc.
Once I’ve got this event rigged up (and un-rigged it with my OnNavigatingFrom event), I can now easily provide physical keys for my power users by enabling the #1 – #5 keys to hold the cards rather than having to move their mouse all over the screen. In addition, I’ve also set the Spacebar up to provide “Deal” functionality, which means they never need the mouse once they start playing the game. Here’s a look at the cards held:
And finally, in case you were wondering, here’s what I drew (I got that wild 2) to get my four of a kind!
Summary
So there you have it. A simple way to capture keystrokes in C# and XAML applications for Windows 8/Windows RT applications. Many apps have a need for this in some way (even if it’s to provide a shortcut or even an Easter Egg), so consider this in your applications as well.
JEFF BLANKENBURG 
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