BUG: KeyDown & KeyUp Events Receive Same Key Codes

• Microsoft Visual Basic Standard and Professional Editions for MS-DOS, version 1.0

SYMPTOMS

In Visual Basic for MS-DOS, the KeyDown and KeyUp events receive the same key codes for some standard ASCII and extended keys. For example, the F1 key and the lowercase "p" both return a KeyCode value of 112. Because the KeyPress event occurs only for standard keys, you can determine which key was pressed by monitoring whether a KeyPress event occurred.

WORKAROUND

You can work around the problem because the KeyDown and KeyUp events are called when you press an extended key, whereas the KeyPress event is called when you press a standard ASCII key. If you set a variable in the KeyPress event, you can then determine if an ASCII key was pressed. An example is shown below in the More Information section.

STATUS

Microsoft has confirmed this to be a bug in the Standard and Professional Editions of Microsoft Visual Basic version 1.0 for MS-DOS. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

This behavior differs from Microsoft Visual Basic for Windows which gives different KeyCode values for standard ASCII versus enhanced keys.

Note that the Form_KeyDown, Form_KeyUp, and Form_KeyPress occur only if there are no controls on the form. To detect keys when you do have controls on a form, you must check for the keys in each control that can have the focus.

There are three form events that can get called when you press a key: KeyDown, KeyPress, and KeyUp. When you press an extended key, only the KeyDown and KeyUp events get called. When you press a standard key, all three events get called.

Step-by-Step Workaround Example

1. Start VBDOS.EXE.



2. From the File menu select New Form... (FORM1.FRM). Form1 is created by default.



3. Exit the Form Designer, save all changes.



4. Add the following code to the module level of Form1:

   
      DIM SHARED Extended AS INTEGER 




5. Add the following code to the Form_KeyDown event procedure of Form1:

   
      SUB Form_KeyDown (KeyCode AS INTEGER, Shift AS INTEGER)
        Extended = -1
      END SUB 




6. Add the following code to the Form_KeyPress event procedure of Form1:

   
      SUB Form_KeyPress (KeyAscii AS INTEGER)
         Extended = 0
      END SUB 




7. Add the following code to the Form_KeyUp event procedure of Form1:

   
      SUB Form_KeyUp (KeyCode AS INTEGER, Shift AS INTEGER)
         Const KEY_F1 = 112
         IF Extended THEN
            SELECT CASE KeyCode
               CASE KEY_F1
                  PRINT "F1"
               ' Add more CASE statements to trap more keys.
            END SELECT
         ELSEIF KeyCode >= 32 OR KeyCode < 127 THEN
            PRINT CHR$(KeyCode)
         END IF
      END SUB 




8. Press F5 to run the application. This program traps the F1 and p keys. To trap more extended keys, add more lines to the SELECT CASE statement. To trap more standard ASCII characters, add more IF statements.

Additional query words: VBmsdos buglist1.00 1.00

Keywords :
Version : MS-DOS:1.0
Platform : MS-DOS
Issue type :