KeyDown, KeyUp Events

Purpose

Occur when the user presses (KeyDown) or releases (KeyUp) a key while an object has the focus.

Syntax

Sub object_KeyDown([index%,] Code&, Shift&)

Sub object_KeyUp([index%,] Code&, Shift&)

object:Ocx Object
index:iexp
Code&, Shift&:Short exp

Description

The KeyDown and KeyUp event syntaxes have these parts:

index% - An integer that uniquely identifies a control or form if it's in an array.

Code& - A key code, such as VK_F1 (the F1 key) or VK_HOME (the HOME key). To specify key codes, use the API VK_* constants. For a comprehensive list of key codes, see Key Codes and ASCII Values.

shift& - An integer that corresponds to the state of the SHIFT, CTRL, and ALT keys at the time of the event. The shift argument is a bit field with the least-significant bits corresponding to the SHIFT key (bit 0), the CTRL key (bit 1), and the ALT key (bit 2).

Shift1
Control2
Alt4

These bits correspond to the values 1, 2, and 4, respectively. Some, all, or none of the bits can be set, indicating that some, all, or none of the keys are pressed. For example, if both CTRL and ALT are pressed, the value of shift is 6.

KeyDown and KeyUp aren't invoked for:

- The ENTER key if the form has a Command control with the Default property set to True.

- The ESC key if the form has a Command control with the Cancel property set to True.

- The TAB key.

KeyDown and KeyUp interpret the uppercase and lowercase of each character by means of two arguments: keycode, which indicates the physical key (thus returning A and a as the same key) and shift, which indicates the state of shift + key and therefore returns either A or a.

Example

Form frm1 = "KeyDown, KeyUp Events", 20, 20, 300, 300

Do

Sleep

Until Me Is Nothing

 

Sub frm1_KeyDown(Code&, Shift&)

Print "KeyDown - Code& = "; Code&

If Shift& And 1

Print "Shift pressed"

Else If Shift& And 2

Print "Ctrl pressed"

Else If Shift& And 4

Print "Alt pressed"

EndIf

EndSub

 

Sub frm1_KeyUp(Code&, Shift&)

Print "KeyUp - Code& = "; Code&

If Shift& And 1

Print "Shift pressed"

Else If Shift& And 2

Print "Ctrl pressed"

Else If Shift& And 4

Print "Alt pressed"

EndIf

EndSub

Remarks

Use the Screen_KeyPreview event to create global keyboard-handling routines. This event sub receives these events before controls or the form receives the events.

Known Issues

According to previous documentation, by setting Code& to 0, the keypress would then be ignored; this does not happen.

To cancel the input from the keyboard, there are two methods available:

  1. Use the Screen_KeyPreview event to catch the key combination early. Then, once you have processed it, set Cancel? to True.

  2. To cancel a simple keypress - let's say you want to disable the letter 'A' on the keyboard - use the older Keypress event as below:

    3. OpenW 1 : Win_1.PrintWrap = True : FontName = "courier new"

    Do : Sleep : Until Win_1 Is Nothing

     

    Sub Win_1_KeyPress(Ascii&)

    If Chr(Ascii&) = "A" Or Chr(Ascii&) = "a"

    Ascii& = 0

    Else

    Print Chr(Ascii&);

    EndIf

    EndSub


  3. However, to intercept and cancel a more complex combination such as Ctrl-V (which is used to paste text in textboxes), a combination of KeyDown and Keypress is required as shown below.

    4. Global diskey?, disv?

    OpenW 1

    Ocx TextBox tb = "", 10, 10, 200, 150 : .MultiLine = True : .BorderStyle = 1

    Ocx Command cmd = "Disable Ctrl-V", 230, 10, 100, 22

    Clipboard.SetText "GFA Basic "

    tb.SetFocus

    Do : Sleep : Until Win_1 Is Nothing

     

    Sub cmd_Click

    Local tbss As Int32 = tb.SelStart // Stores Textbox Caret position

    If disv? Then cmd.Caption = "Disable Ctrl-V"

    If Not disv? Then cmd.Caption = "Enable Ctrl-V"

    disv? = Not disv?

    tb.SetFocus                       // Returns focus to Textbox

    tb.SelStart = tbss                // Replaces the caret where it was

    EndSub

     

    Sub tb_KeyDown(Code&, Shift&)

    Debug Code&

    If disv?                       // If Ctrl-V is disabled

    If Shift& = 2 And Code& = 86 // If Ctrl-V pressed

    diskey? = True             // Disable Keypress

    EndIf

    EndIf

    EndSub

     

    Sub tb_KeyPress(Ascii&)

    If diskey?

    Ascii& = 0          // Cancels the keypress

    diskey? = False     // Resets the diskey? flag

    EndIf

    EndSub

    On occasions when using the example above with different 'shift key' combinations, the key press after the disqualified key combination may be ignored or not printed; if this happens, insert 'diskey? = False' as the first line of the KeyDown sub.

See Also

Form, KeyPress, Screen_KeyPreview

{Created by Sjouke Hamstra; Last updated: 01/03/2017 by James Gaite}