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Wednesday, October 15, 2008

Displaying keyboard keypress values in C#

Following code will display the names of all keys pressed by the user.(Press x to exit)

// This example demonstrates:
// the Console.CancelKeyPress event,
// the ConsoleCancelEventHandler delegate,
// the ConsoleCancelEventArgs.SpecialKey property, and
// the ConsoleCancelEventArgs.Cancel property.
using System;
class ConsoleApplication1
{
public static void Main()
{
ConsoleKeyInfo cki;
// Clear the screen.
Console.Clear();
// Turn off the default system behavior when CTRL+C is pressed. When
// Console.TreatControlCAsInput is false, CTRL+C is treated as an
// interrupt instead of as input.
Console.TreatControlCAsInput = false;
// Establish an event handler to process key press events.
Console.CancelKeyPress += new ConsoleCancelEventHandler(myHandler);
while (true)
{
// Prompt the user.
Console.Write("Press any key, or 'X' to quit, or ");
Console.WriteLine("CTRL+C to interrupt the read operation:");
// Start a console read operation. Do not display the input.
cki = Console.ReadKey(true);
// Announce the name of the key that was pressed .
Console.WriteLine(" Key pressed: {0}\n", cki.Key);
// Exit if the user pressed the 'X' key.
if (cki.Key == ConsoleKey.X) break;

}
}
/*
When you press CTRL+C, the read operation is interrupted and the
console cancel event handler, myHandler, is invoked. Upon entry
to the event handler, the Cancel property is false, which means
the current process will terminate when the event handler terminates.
However, the event handler sets the Cancel property to true, which
means the process will not terminate and the read operation will resume.
*/
protected static void myHandler(object sender, ConsoleCancelEventArgs args)
{
// Announce that the event handler has been invoked.
Console.WriteLine("\nThe read operation has been interrupted.");
// Announce which key combination was pressed.
Console.WriteLine(" Key pressed: {0}", args.SpecialKey);
// Announce the initial value of the Cancel property.
Console.WriteLine(" Cancel property: {0}", args.Cancel);
// Set the Cancel property to true to prevent the process from terminating.
Console.WriteLine("Setting the Cancel property to true...");
args.Cancel = true;
// Announce the new value of the Cancel property.
Console.WriteLine(" Cancel property: {0}", args.Cancel);
Console.WriteLine("The read operation will resume...\n");
}
}
/*
This code example produces results similar to the following text:
Press any key, or 'X' to quit, or CTRL+C to interrupt the read operation:
Key pressed: J
Press any key, or 'X' to quit, or CTRL+C to interrupt the read operation:
Key pressed: Enter
Press any key, or 'X' to quit, or CTRL+C to interrupt the read operation:
The read operation has been interrupted.
Key pressed: ControlC
Cancel property: False
Setting the Cancel property to true...
Cancel property: True
The read operation will resume...
Key pressed: Q
Press any key, or 'X' to quit, or CTRL+C to interrupt the read operation:
Key pressed: X
*/

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