I had built onscreen keyboards for several software applications, but I had never made one full-fledged keyboard with 101+ keys. So, I decided to tackle this project and build my onscreen keyboard in C#. In this article, I have shared my approach and the source code, so you will have a starting point if you wish to continue.
If you have ever built software for touchscreen devices, you know that having an onscreen keyboard is an essential component. Windows comes with an Onscreen keyboard as one of its built-in Ease of Access tools.
Windows OSK is a solution, but you don’t have much control over its functions and behavior, let alone building new tasks to it!
In this article, I show what are the basic methods to build an onscreen keyboard for Windows and customize it.
I had built onscreen keyboards for several software applications, but I had never made one full-fledged keyboard with 101+ keys. In a recent project, we needed a complete onscreen keyboard to be included and we can control it.
So, I ended working on this project and what you see here is the results of my work. You can expand it and build it to suit your needs.
The Key Method
The “key” to build your Onscreen Keyboard, is to use
This method sends keystrokes to the active application. For example, if you want to click a button and send the
TAB keystroke, you use the following method:
If your request does not represent valid keystrokes, you will get an
ArgumentException in your code.
- Sometimes, you need to send more than one character to get a specific key.
For example, to specify the open parentheses sign, use “
- The plus sign (+), caret (^), percent sign (%), tilde (~), and parentheses () have special meanings to
SendKeys. To specify one of these characters, enclose it within braces
- To specify characters that aren’t displayed when you press a key, such as ENTER or TAB, and keys that represent actions rather than characters, you must use specific codes.
Handling SHIFT, CTRL, and ALT
Combination keys, such as CTRL + Key, SHIFT + Key, and ALT + Key, are possible by using caret (^), plus(+), and percent sign (%).
To specify to hold down CTRL while S is pressed, followed by D without SHIFT, use “^SD”.
To specify to hold down SHIFT and press A and B, use “+(AB)”.
Planning the Keyboard Layout
I decided to go by the layout of my physical keyboard:
I opened a new C# Winforms with the .NET Framework project in Visual Studio.
I added my keys, according to the physical keyboard layout:
For the majority of the keys, you can use a button control, except for these special keys, which need to be
So, when the CAPSLOCK key is in the on mode, you have a checked
CheckBox that identifies capital letters. CAPSLOCK off creates keystrokes for lowercase letters.
For keys with two characters, such as 2 (@) or 7 (&), we have to check the status of the SHIFT button and generate the proper keystroke accordingly.
SHIFT + 2 should send
Similar situations apply to the combination keys such as CTRL + C (Copy), CTRL + P (Paste), and so on.
if (capslock.Checked || lshift.Checked || rshift.Checked)
SendKeys.Send("B"); lshift.Checked = false; rshift.Checked = false;
To identify when any of the checkboxes are in a checked state, I use background color:
if (capslock.Checked == true)
capslock.BackColor = System.Drawing.ColorTranslator.FromHtml("#0076D7");
capslock.BackColor = System.Drawing.ColorTranslator.FromHtml("#333333");
Now that I have complete control of my onscreen keyboard, I want to add custom keys. Imagine Custom keys as a shortcut to send two or more characters in one keystroke.
Some more cosmetic details include adding a row with CAPS, Insert, and NUM LOCK key status. I change the visibility of the labels for CAPS and NUM depends on the On or Off status of the corresponding keys. I also added the code to change the background color of the keys as you hover the mouse over them.
Border Style Issue
If you select the None option from your form properties for the
FormBorderStyle, you will not be able to move your keyboard around the screen and change its position.
If you don’t mind the standard Windows border, you can choose an option that best fits your taste and usage of your keyboard.
I wanted to get rid of the border and have my border style. So this is what I have done:
- I set the
- Placed all my keys to a
panel, which is sitting on the main form
- Changed the form’s background color to create a contrast with the
panel’s background color
Now I have my colors and make-shift border, but how can I move my onscreen keyboard?
The trick here requires a Win32 API:
[DllImportAttribute("user32.dll")] public static extern int SendMessage
(IntPtr hWnd, int Msg, int wParam, int lParam);
[DllImportAttribute("user32.dll")] public static extern bool ReleaseCapture();
private void Form1_MouseDown(object sender, MouseEventArgs e)
if (e.Button == MouseButtons.Left)
SendMessage(Handle, WM_NCLBUTTONDOWN, HT_CAPTION, 0);
I have an onscreen keyboard with customized background and border style, which I can move around the screen and add custom keys to it.
Points of Interest
As I was working on this project, I came up with so many ideas to expand the normal onscreen keyboard to something much more. The Custom keys was one that I implemented in this code.
- 9th August, 2021: First release of this code
I hope to get another chance to work on this project again, and perhaps port it to Xamarin.