WPF: Virtual Keyboard

Creating a virtual keyboard in WPF can be quite an obstacle. As far as I can tell, WPF does not directly support simulating keyboard strokes. As a result, you have two options:

• Import the SendInput function from a C++ DLL (User32.dll i believe it is)
• Manually write the output in the cases you want to.

The 2nd option isn't too bad to handle. This way also prevents you from having to handle each button separately, but I'm sure you could work around that in a way similar to what I've done here.

Basically, create your keyboard layout within it's own panel or grid, with each key being a button. Once you've done this, you can do a foreach loop on each button, where if it's a letter (usually the Button.Content.Length == 1), send it to one event handler, otherwise, send the button to a special event handler. Also, make sure every button is not focusable (Button.IsFocusable = false).

1foreach (Button b in KeyboardPanel.Children)
2{
3    b.Focusable = false;
4
5    if (b.Content.ToString().Length <= 1)
6    {
7        b.Click += new RoutedEventHandler(keyboardButton_Click);
8    }
9    else
10    {
11        b.Click += new RoutedEventHandler(keyboardButtonSpecial_Click);
12    }
13} 

Once you've done this, the implementation is similiar to this:

662
663
664
665        void keyboardButtonSpecial_Click(object sender, RoutedEventArgs e)
666        {
669            switch (((Button)sender).Content.ToString())
670            {
671                case "Space":
672                    if (System.Windows.Input.Keyboard.FocusedElement.GetType() == typeof(TextBox))
673                    {
674                        TextBox box = ((TextBox)System.Windows.Input.Keyboard.FocusedElement);
675                        int newIndex = box.CaretIndex + 1;
676                        box.Text = box.Text.Insert(box.CaretIndex, " ");
677                        box.CaretIndex = newIndex;
678                    }
679                    break;
680                case "Shift":
681                    if (isKeyboardUppercase())
682                        setKeyboardUppercase(false);
683                    else
684                        setKeyboardUppercase(true);
685                    break;
686                case "Tab":
687                    ((UIElement)System.Windows.Input.Keyboard.FocusedElement).MoveFocus(new System.Windows.Input.TraversalRequest(System.Windows.Input.FocusNavigationDirection.Next));
688                    break;
689                case "Delete":
690                    if (System.Windows.Input.Keyboard.FocusedElement.GetType() == typeof(TextBox))
691                    {
692                        System.Windows.Forms.SendKeys.SendWait("{BACKSPACE}");
693                    }
694                    break;
695                case "Enter":
696                    if (System.Windows.Input.Keyboard.FocusedElement.GetType() == typeof(TextBox))
697                    {
698                        TextBox box = ((TextBox)System.Windows.Input.Keyboard.FocusedElement);
699                        if (box.AcceptsReturn)
700                        {
701                            int nIndex = box.CaretIndex + 1;
702                            box.Text = box.Text.Insert(box.CaretIndex, Environment.NewLine);
703                            box.CaretIndex = nIndex;
704                        }
705                    }
706                    break;
707            }
708        }
709
710        bool isKeyboardUppercase()
711        {
712            if (Char.IsUpper((keyboardLetterA.Content.ToString().ToCharArray())[0]))
713                return true;
714            else
715                return false;
716        }
717
718        void setKeyboardUppercase(bool upper)
719        {
720            foreach (Button b in KeyboardPanel.Children)
721            {
722                if (b.Content.ToString().Length <= 1
723                {
724                    if (upper)
725                        b.Content = b.Content.ToString().ToUpper();
726                    else
727                        b.Content = b.Content.ToString().ToLower();
728                }
729            }
730        }
731
732        void keyboardButton_Click(object sender, RoutedEventArgs e)
733        {
735            if (System.Windows.Input.Keyboard.FocusedElement.GetType() == typeof(TextBox))
736            {
737                TextBox box = ((TextBox)System.Windows.Input.Keyboard.FocusedElement);
738                int newIndex = box.CaretIndex + 1;
739                box.Text = box.Text.Insert(box.CaretIndex, ((Button)sender).Content.ToString());
740                box.CaretIndex = newIndex;
741
742                if (Char.IsUpper((((Button)sender).Content.ToString().ToCharArray())[0]))
743                {
744                    setKeyboardUppercase(false);
745                }
746
747            }
748        }
749        #endregion

In here, you can see I've got several things going on. If you push Shift on my keyboard, it'll change the content of the letters to uppercase or lowercase, based on what they already were. (I test this by looking at the letter A key's content).

I also only type if we're currently focused into a TextBox. For the program I was using this in, I had no need for typing unless we're focused in a TextBox. Since i know I'm in a TextBox, i can look for the Caret and type at that point.

Look at the "DELETE" Key (it's actually Backspace, it was just improperly named). I've left this bad code "as-is" to show the other way you could handle some input. If I'm in WPF, obviously I would like to keep Windows Forms out of my application if possible. After looking at this, the answer seemed somewhat obvious (and similiar to all the other methods of input):

1                case "Delete":
2                    if (System.Windows.Input.Keyboard.FocusedElement.GetType() == typeof(TextBox))
3                    {
4                        TextBox box = ((TextBox)System.Windows.Input.Keyboard.FocusedElement);
5                        int newIndex = box.CaretIndex - 1;
6                        if (newIndex >= 0)
7                        {
8                            box.Text = box.Text.Remove(box.CaretIndex - 1, 1);
9                            box.CaretIndex = newIndex;
10                        }
11                    }
12                    break;

This method handles deleting characters in logic, and now eliminates the need for System.Windows.Forms.

The applications for a virtual keyboard like this? I'd say for added accessibility, and touch-screen applications where users may not want to move their fingers from the monitor to a keyboard for typing small things.