Keyboard Input

Keyboard input has some “limitations” due mainly on how Linux handle the keyboards on terminal:

• No key up event. Only the key down event is available. This is because in Linux terminal there is no keyboard concept: only characters coming to your application.
• Some different key combinations generate the same output character, making impossible for TVision2 to detect keystrokes like Ctrl+I (because generates the TAB character) or Ctrl+M because generates the CR generated also by the ENTER key.

Currently if running under Windows, these combinations (like Ctrl+I) are properly handled. This can lead to a different behavior of the application when running under Linux or under Windows, and it will be addressed on a future release.

Processing Keyboard events

You need a behavior to process a keyboard event. In the Update method the BehaviorContext<T> parameter received contains a Events property (of type ITvConsoleEvents) which all events (pending to process) for this iteration. You can use the methods of this property to get a keyboard event and inspect it:

public bool Update(BehaviorContext<TControlState> updateContext)
{
    if (!updateContext.Events.HasKeyboardEvents) return false;
    var keyEvents = updateContext.Events.KeyboardEvents;
    var consoleKeyInfo = evt.AsConsoleKeyInfo();      // Returns the event as a System.ConsoleKeyInfo struct
    if (...) {
      evt.Handle();       // Mark this event as "Handled". 
    }
}

Handling events

Events can be marked as “handled” by calling its Handle() method. When a keyboard event is marked as “handled” it is no longer returned in the ITvConsoleEvents.KeyboardEvents property, so it won’t be available for the next behaviors. A behavior can process an event and not call its Handle() method. In this case, this same event will be available to the next behavior, so it could be processed twice (or more).

As getting the first available (non handled) keyboard event is a typical scenario the ITvConsoleEvents interface provides a convenient method called AcquireFirstKeyboard:

var @event = events.AcquireFirstKeyboard(evt => evt.AsConsoleKeyInfo().Key == _hotkey, autoHandle: true);

You need to pass a predicate, and the method will return the first non handled event that satisfies this predicate (if any). The autoHandle parameter controls if the event is marked as handled when is returned. If its value is false you need to manually handle the event (calling Handle()) if appropiate.

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