/// <summary>
/// Determines whether the specified object can be converted into a <see cref="String"/>.
/// </summary>
/// <param name="value">The object to evaluate for conversion.</param>
/// <param name="context">Context information that is used for conversion.</param>
/// <returns>
/// <see langword="true"/> if the <paramref name="value"/> can be converted into a
/// <see cref="String"/>; otherwise, <see langword="false"/>.
/// </returns>
public override bool CanConvertToString(object value, IValueSerializerContext context)
{
var gesture = value as MultiKeyGesture;
return(gesture != null &&
ModifierKeysConverter.IsDefinedModifierKeys(gesture.Modifiers) &&
MultiKeyGestureConverter.IsDefinedKey(gesture.Key));
}
private void OnPreviewKeyDown(object sender, KeyEventArgs eventArgs)
{
if ((eventArgs == null) || !MultiKeyGestureConverter.IsDefinedKey(eventArgs.Key))
{
Reset();
return;
}
var timeSinceLastKeyPress = TimeSpan.FromMilliseconds(eventArgs.Timestamp - _lastKeyPress);
if (timeSinceLastKeyPress > MaximumDelayBetweenKeyPresses)
{
// Took too long to press next key.
Reset();
return;
}
if (ShouldIgnoreKey(eventArgs.Key))
{
// When a modifier key is set, we ignore certain keys (LeftCtrl, RightCtrl, ...).
// I.e. the user can release/press LeftCtrl multiple times. We only track the relevant keys.
eventArgs.Handled = true;
return;
}
if (eventArgs.Key == Key.Escape)
{
// Cancel multi-key gesture.
eventArgs.Handled = true;
Reset();
return;
}
if (Keyboard.Modifiers != Modifiers)
{
// Wrong modifiers.
Reset();
return;
}
Debug.Assert(_currentKeyIndex > 0, "At least one key of MultiKeyGesture should have been pressed.");
if (_keys[_currentKeyIndex] != eventArgs.Key)
{
// Wrong key pressed.
Reset();
return;
}
_currentKeyIndex++;
if (_currentKeyIndex < _keys.Count)
{
// We are still in the multi-key gesture, waiting for next key stroke.
_lastKeyPress = eventArgs.Timestamp;
eventArgs.Handled = true;
return;
}
// Match complete!
// Report a success on the next call of Matches().
_reportMatch = true;
// Set eventArgs.Handled to prevent other key gestures from firing.
// For example: If we have detected "Ctrl+K, Ctrl+X" then we do not want "Ctrl+X" (Cut)
// to be fired.
eventArgs.Handled = true;
// However, now we have a problem! eventArgs.Handled is set, so the KeyDown event is
// canceled and Matches() never gets called. To solve this problem, we re-raise a dummy
// KeyDown event with Key.None. This way Matches() gets called again.
// [MartinG: Sorry, for this little "hack", but this is the only way, we can prevent
// conflicting key gestures such as "Ctrl+X" (Cut) from firing.]
_currentTarget.Dispatcher.BeginInvoke(
DispatcherPriority.Input,
new Action(
() => _currentTarget.RaiseEvent(
new KeyEventArgs(
eventArgs.KeyboardDevice,
eventArgs.InputSource,
eventArgs.Timestamp,
Key.None)
{
RoutedEvent = Keyboard.KeyDownEvent
}))
);
}
public override bool Matches(object targetElement, InputEventArgs inputEventArgs)
{
if (_currentTarget != null)
{
if (_currentTarget == targetElement)
{
if (_reportMatch)
{
// We have already checked the key (see OnPreviewKeyDown) and found a match.
Reset();
return(true);
}
else
{
// We have already installed an event handler:
// The check is happening in OnPreviewKeyDown. We can exit here.
return(false);
}
}
else
{
// We are already within a multi-key gesture. But suddenly the targetElement has changed.
Reset();
}
}
KeyEventArgs eventArgs = inputEventArgs as KeyEventArgs;
if ((eventArgs == null) || !MultiKeyGestureConverter.IsDefinedKey(eventArgs.Key))
{
return(false);
}
// ----- Check first key stroke
if (Keyboard.Modifiers != Modifiers)
{
// Wrong modifiers.
return(false);
}
if (eventArgs.Key != _keys[0])
{
// Wrong key.
return(false);
}
// First key matches!
_lastKeyPress = eventArgs.Timestamp;
if (_keys.Count == 1)
{
// The current multi-key gesture only has one key.
return(true);
}
// We need to check more than one key.
// --> Install an event handler for PreviewKeyDown.
UIElement uiElement = targetElement as UIElement;
if (uiElement == null)
{
// We currently can only check for multiple keys if the target is an UIElement.
throw new InvalidOperationException(Invariant($"MultiKeyGesture has invalid target element ({targetElement}). The target element needs to be of type UIElement."));
}
_currentTarget = uiElement;
_currentTarget.PreviewKeyDown += OnPreviewKeyDown;
_currentKeyIndex = 1;
return(false);
}