Using Keyboard Input in WPF - Page 2
       by kirupa  |  7 March 2007

In the previous page you downloaded the partial source file and received a quick tour of what the code does. In this page let's write some code and create something useful using keyboard input.

Detecting the Key Pressed
Let's start by detecting which key was pressed. For example, let's say that every time the letter K is pressed, we play a default system sound. The code for doing that would be:

private void KeyDownEventHanlder(object sender, KeyEventArgs e)

{

if (e.Key == Key.K)

{

System.Media.SystemSounds.Exclamation.Play();

}

}

If you were to add the above non-grayed out lines to your KeyDownEventHandler method and run the program, everything still looks the same. When you start typing in your textbox, and more importantly, when you hit the letter K on your keyboard, the default Windows exclamation sound will play. All of your other keys simply display their letters on the screen, but you single out the letter K to also play a sound when pressed.

Let's look in detail at how the key detection works. First, I access my event argument e's Key property:

private void KeyDownEventHanlder(object sender, KeyEventArgs e)

{

if (e.Key == Key.K)

{

System.Media.SystemSounds.Exclamation.Play();

}

}

The Key property keeps track of the key currently being pressed because your KeyDownEventHandler runs every time you press down on a Key. I place e.Key as part of a condition for my if statement because I want to check whether the key currently pressed matches the key that I want pressed, which is K:

private void KeyDownEventHanlder(object sender, KeyEventArgs e)

{

if (e.Key == Key.K)

{

System.Media.SystemSounds.Exclamation.Play();

}

}

The check whether our e.Key value is equal to the letter K which is represented by Key.K. When the letter pressed matches the letter we want, the if statement becomes true and whatever we wish to execute....well, executes!

This is great for individual letters, but what if you want to provide some sort of Save functionality where your users have to press two keys such as Ctrl + S? The above approach won't work too well, solet's look at how to do that in the next section.

Note

The information from the following section is almost entirely based on my blog post on this topic: http://blog.kirupa.com/?p=68

Detecting Key Combinations
Key combinations are a fancy pair of words to describe pressing/holding multiple keyboard buttons to perform a command. For example, if you have ever used Ctrl + S to Save, Ctrl + C, to Copy, or Alt + F4 to close an application, then you have used key combinations. There are many such combinations, and while I provided some common ones, many applications ranging from Flash to Visual Studio provide their own key combinations to help save you some time. Let's add some key combinations to our little program also.

To add key combinations, modify/overwrite your KeyUpEventHandler with the following code:

private void KeyUpEventHanlder(object sender, KeyEventArgs e)

{

// Ctrl + S

if ((Keyboard.Modifiers == ModifierKeys.Control) && (e.Key == Key.S))

{

MessageBox.Show("Save!");

}

 

// Ctrl + N

if ((Keyboard.Modifiers == ModifierKeys.Control) && (e.Key == Key.N))

{

MessageBox.Show("New!");

}

 

// Ctrl + O

if ((Keyboard.Modifiers == ModifierKeys.Control) && (e.Key == Key.O))

{

MessageBox.Show("Open!");

}

}

If you run your application again and give your textbox focus (i.e. clicking inside it), pressing either Ctrl + S, Ctrl + N, or Ctrl + O will display a corresponding dialog box. On the next page, let's look at the interesting parts of the above code that cause it to work in greater detail!

Onwards to the next page!

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