Console.CancelKeyPress Console.CancelKeyPress Console.CancelKeyPress Console.CancelKeyPress Event

Definition

Occurs when the Control modifier key (Ctrl) and either the C console key (C) or the Break key are pressed simultaneously (Ctrl+C or Ctrl+Break).

public:
 static event ConsoleCancelEventHandler ^ CancelKeyPress;
public static event ConsoleCancelEventHandler CancelKeyPress;
member this.CancelKeyPress : ConsoleCancelEventHandler 
Public Shared Custom Event CancelKeyPress As ConsoleCancelEventHandler 

Examples

The following example demonstrates how the CancelKeyPress event is used. When you press Ctrl+C, the read operation is interrupted and the myHandler event handler is invoked. Upon entry to the event handler, the ConsoleCancelEventArgs.Cancel property is false, which means that the current process will terminate when the event handler terminates. However, the event handler sets the ConsoleCancelEventArgs.Cancel property to true, which means that the process will not terminate and the read operation will resume.

using namespace System;

void OnCancelKeyPressed(Object^ sender, 
    ConsoleCancelEventArgs^ args)
{
    Console::WriteLine("{0}The read operation has been interrupted.",
        Environment::NewLine);

    Console::WriteLine("  Key pressed: {0}", args->SpecialKey);

    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...{0}",
        Environment::NewLine);
}

int main()
{       
    // Clear the screen.
    Console::Clear();

    // Establish an event handler to process key press events.
    Console::CancelKeyPress += 
        gcnew ConsoleCancelEventHandler(OnCancelKeyPressed);

    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.
        ConsoleKeyInfo^ keyInfo = Console::ReadKey(true);

        // Announce the name of the key that was pressed .
        Console::WriteLine("  Key pressed: {0}{1}", keyInfo->Key, 
            Environment::NewLine);

        // Exit if the user pressed the 'X' key.
        if (keyInfo->Key == ConsoleKey::X)
        {
            break;
        }
    }
}
// The example displays output similar to the following:
//    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
using System;

class Sample 
{
    public static void Main()
    {
        ConsoleKeyInfo cki;

        Console.Clear();

        // Establish an event handler to process key press events.
        Console.CancelKeyPress += new ConsoleCancelEventHandler(myHandler);
        while (true) {
            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;
        }
    }

    protected static void myHandler(object sender, ConsoleCancelEventArgs args)
    {
        Console.WriteLine("\nThe read operation has been interrupted.");

        Console.WriteLine("  Key pressed: {0}", args.SpecialKey);

        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");
    }
}
// The example displays output similar to the follwoing:
//    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
Class Sample
    Public Shared Sub Main() 
        Dim cki As ConsoleKeyInfo
        
        Console.Clear()
        
        ' Establish an event handler to process key press events.
        AddHandler Console.CancelKeyPress, AddressOf myHandler

        While True
            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}" & vbCrLf, cki.Key)
            
            ' Exit if the user pressed the 'X' key.
            If cki.Key = ConsoleKey.X Then Exit While
        End While
    End Sub

    Protected Shared Sub myHandler(ByVal sender As Object, _
                                   ByVal args As ConsoleCancelEventArgs) 
        Console.WriteLine(vbCrLf & "The read operation has been interrupted.")
        
        Console.WriteLine("  Key pressed: {0}", args.SpecialKey)
        
        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..." & vbCrLf)
    End Sub
End Class
' The example diplays output similar to the following:
'    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

Remarks

This event is used in conjunction with System.ConsoleCancelEventHandler and System.ConsoleCancelEventArgs. The CancelKeyPress event enables a console application to intercept the Ctrl+C signal so the event handler can decide whether to continue executing or terminate. For more information about handling events, see Handling and Raising Events.

When the user presses either Ctrl+C or Ctrl+Break, the CancelKeyPress event is fired and the application's ConsoleCancelEventHandler event handler is executed. The event handler is passed a ConsoleCancelEventArgs object that has two useful properties:

  • SpecialKey, which allows you to determine whether the handler was invoked as a result of the user pressing Ctrl+C (the property value is ConsoleSpecialKey.ControlC) or Ctrl+Break (the property value is ConsoleSpecialKey.ControlBreak).

  • Cancel, which allows you to determine how to your application should respond to the user pressing Ctrl+C or Ctrl+Break. By default, the Cancel property is false, which causes program execution to terminate when the event handler exits. Changing its property to true specifies that the application should continue to execute.

Tip

If your application has simple requirements, you can use the TreatControlCAsInput property instead of this event. By setting this property to false, you can ensure that your application always exits if the user presses Ctrl+C. By setting it to true, you can ensure that pressing Ctrl+C will not terminate the application.

The event handler for this event is executed on a thread pool thread.

Security

UIPermission
for modifying safe top-level windows and subwindows. Associated enumeration: SafeTopLevelWindows

Applies to

See Also