Tip 174: Using the GetKeyState Function to Determine the State of Virtual Keys

December 5, 1995

Abstract

This article explains how to retrieve the current state of any virtual key in a Microsoft® Visual Basic® application.

Determining the State of Virtual Keys

The Microsoft® Windows® application programming interface (API) GetKeyState function can be used in a Microsoft Visual Basic® application to retrieve the current state of any virtual key. To use this function, include the following Declare statement in the General Declarations section of your form:

Private Declare Function GetKeyState Lib "user32" (ByVal nVirtKey As Long) As
   Integer

The GetKeyState function will return the state (key is up, key is down, key is toggled on or off) of the virtual key you pass to the function.

In the example program below, you want to retrieve the state of the three toggle keys—caps lock, num lock, and scroll lock. To do this, you call the GetKeyState function with the virtual-key code for each individual key you want to test. For example, to retrieve the state of the caps lock key, you execute the statement:

Key = GetKeyState(VK_CAPITAL)

The value returned by the GetKeyState function can then be tested. If the low-order bit is 1, then the toggle key is on. If the low-order bit is 0, then the toggle key is off. Therefore, you can use the statement:

If Key And 1 Then

to test if the toggle key is on.

Example Program

This program shows how to use the GetKeyState function to determine whether a toggle key (caps lock, num lock, scroll lock) is on or off.

1. Create a new project in Visual Basic. Form1 is created by default.
   
   
2. Add the following Constant and Declare statements to the General Declarations section of Form1 (note that the Declare statement must be typed as a single line of code):

   Private Declare Function GetKeyState Lib "user32" (ByVal nVirtKey As Long) 
      As Integer
   Const VK_NUMLOCK = &H90
   Const VK_SCROLL = &H91
   Const VK_CAPITAL = &H14
   

3. Add a Command Button control to Form1. Command1 is created by default.
   
   
4. Add the following code to the Click event for Command1.

   Private Sub Command1_Click()
       Dim Key As Integer
   
       Key = GetKeyState(VK_NUMLOCK)
       If Key And 1 Then
           text1.Text = "Num Lock is On"
       Else
           text1.Text = "Num Lock is Off"
       End If
   
       Key = GetKeyState(VK_SCROLL)
       If Key And 1 Then
           Text2.Text = "Scroll Lock is On"
       Else
           Text2.Text = "Scroll Lock is Off"
       End If
   
       Key = GetKeyState(VK_CAPITAL)
       If Key And 1 Then
           Text3.Text = "Caps Lock is On"
       Else
           Text3.Text = "Caps Lock is Off"
       End If
   End Sub
   

5. Add three Text Box controls to Form1. Text1, Text2, and Text3 are created by default.

Run the example program by pressing f5. Click the Command Button. The state of the num lock, scroll lock, and caps lock keys appears in the corresponding Text Box controls.