<Previous Lesson> <<Home>> <Next Lesson>

In previous lessons, we have only learned how to trigger events or control program flow  by clicking the mouse. In this chapter, you will learn how to use the keyboard to trigger an event using the keyboard beside using the mouse. When the user presses a key on the keyboard, it will trigger an event or a series of events. These events are called the keyboard events. In Visual Basic, the three basic event procedure to handle the key events are KeyPress, Keydown and KeyUp

38.1 ASCII

The key event occurs when the user presses any key that corresponds to a certain alphanumeric value or an action such as Enter, spacing, backspace and more. Each of those value or action is represented by a set of code known as the ASCII . ASCII stands for American Standard Code for Information Interchange.  ASCII stands for American Standard Code for Information Interchange. Computers can only understand numbers, so an ASCII code is the numerical representation of a character such as 'a' or '@' or an action of some sort. ASCII was developed a long time ago and now the non-printing characters are rarely used for their original purpose.In order to write code for the Key events , we need to know the ASCII and the corresponding values. Some of the commond ASCII values are  shown in Table 38.1.

Table 38.1: ASCII Values

For more detail table, please refer to  http://www.asciitable.com/

38.2 Common Key Events Constants.

In Visual Basic 6, it employs a set of constants that correspond to the ASCII values. We can use the constants instead of the ASCII. The following tablle shows the constants and the corresponding ASCII values.

38.3 Writing code for the key events

 We can write code for the three key events i.e. keyPress, KeyDown and KeyUp.

Example 38.1

Private Sub Form_KeyPress(KeyAscii As Integer)
If KeyAscii = 13 Then  ' 13 is the ASCII value for the Enter key
Print "You have pressed the Enter key"
Else
Print "You have pressed other key"

End If

End Sub

 

In this example, the program can detect the pressing of Enter key and the keys other than the Enter key.

Example 38.2

If you wish to detect and display the key pressed by the user, simply type the following code:

Private Sub Form_KeyPress(KeyAscii As Integer)

Print Chr(KeyAscii)

End Sub

The function Chr will convert the ASCII values to the corresponding characters as shown in the ASCII table.

Example 38.3

Private Sub Form_KeyPress(KeyAscii As Integer)

For i = 65 To 90
Print Chr(KeyAscii)
Next

End Sub

In this example, we use the For ...Next loop to display the alphabet A to Z by pressing any key on the keyboard.

Example 38.4

Private Sub Form_KeyPress(KeyAscii As Integer)

If KeyAscii = 13 Then
For i = 97 To 122
Print Chr(i)
Next
End If

End Sub