Learn Visual Basic 6.0

2. The Visual Basic Language

Example 2-2: Savings Account - Key Trapping

1. Note the acceptable ASCII codes are 48 through 57 (numbers), 46 (the decimal point), and 8 (the backspace key). In the code, we use symbolic constants for the numbers and backspace key. Such a constant does not exist for the decimal point, so we will define one with the following line in the general declarations area:
   
   Const vbKeyDecPt = 46
   
   
2. Add the following code to the three procedures: txtDeposit_KeyPress, txtInterest_KeyPress, and txtMonths_KeyPress.
   
   Private Sub txtDeposit_KeyPress (KeyAscii As Integer)
   �Only allow number keys, decimal point, or backspace
   If (KeyAscii >= vbKey0 And KeyAscii <= vbKey9) Or KeyAscii = vbKeyDecPt Or KeyAscii = vbKeyBack Then
   Exit Sub
   Else
   KeyAscii = 0
   Beep
   End If
   End Sub
   
   Private Sub txtInterest_KeyPress (KeyAscii As Integer)
   �Only allow number keys, decimal point, or backspace
   If (KeyAscii >= vbKey0 And KeyAscii <= vbKey9) Or KeyAscii = vbKeyDecPt Or KeyAscii = vbKeyBack Then
   Exit Sub
   Else
   KeyAscii = 0
   Beep
   End If
   End Sub
   
   Private Sub txtMonths_KeyPress (KeyAscii As Integer)
   �Only allow number keys, decimal point, or backspace
   If (KeyAscii >= vbKey0 And KeyAscii <= vbKey9) Or KeyAscii = vbKeyDecPt Or KeyAscii = vbKeyBack Then
   Exit Sub
   Else
   KeyAscii = 0
   Beep
   End If
   End Sub
   
   (In the If statements above, note the word processor causes a line break where there really shouldn�t be one. That is, there is no line break between the words Or KeyAscii and = vbKeyDecPt. One appears due to page margins. In all code in these notes, always look for such things.)
   
   
3. Rerun the application and test the key trapping performance.

Counter Hit


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