Writing a keyboard interception program using VB

We know that in some programs, there are some shortcuts (such as: Shift key to minimize, ESC key to exit, Ctrl+S to save, Alt+x to exit, etc.). There have been some introductions in the past that it can be done using the Win32 API, but it is too cumbersome. In fact, VB itself has already provided us with this function.

Let's create a new form Form1. For keyboard operations, we can see three events: KeyPress(), KeyDown and KeyUp. I will introduce them respectively below:

The KeyPress() event occurs when the user presses and releases an ANSI key (ANSI is the visible ASCII characters 1-127).

grammar

Private Sub object_KeyPress(［index As Integer,］keyascii As Integer) KeyPress event syntax contains the following parts:

partial description

object is an object expression whose value is "applied to" an object in the list.

index is an integer that uniquely identifies a control in the control array (only available for control arrays).

keyascii is an integer that returns a standard numeric ANSI key code. Keyascii passes an object by reference, making changes to it possible.

Send a different character. Changing keyascii to 0 cancels the keystroke so that the object receives no characters.

illustrate

The object with focus receives this event. A form can receive this event only if the KeyPreview property is set to True. A KeyPress event can reference any printable keyboard character, a character from the standard alphabet or one of a few special characters in combination with the CTRL key, and the ENTER or BACKSPACE key. The KeyPress() event procedure is useful when intercepting keystrokes entered in a TextBox or ComboBox control. It can instantly test the validity of keystrokes or format characters as they are entered. Changing the value of the keyascii parameter will change the characters displayed.

You can use the following expression to convert the keyascii parameter to a character:

Chr(KeyAscii) then performs string manipulation and back-translates the character into an ANSI number that the control can interpret through this expression: KeyAscii = Asc(char) Functionality that cannot be handled by KeyPress() can be handled by KeyDown() and KeyUp () event to handle: Syntax Private Sub object_KeyDown([index As Integer,] keycode As Integer, shift As Integer) Private Sub object_KeyUp([index As Integer,] keycode As Integer, shift As Integer) KeyDown and KeyUp events include the following parts: Part Description object An object expression whose value is "applied" to an object in the list. Index is an integer, which is used to uniquely identify a control in the control array (only available for control arrays). keycode is a key code, such as vbKeyF1 (F1 key) or vbKeyHome (HOME key). shift is an integer that responds to the state of the SHIFT, CTRL, and ALT keys when this event occurs. The shift, CTRL, and ALT keys correspond to the values ​​1, 2, and 4 in these bits, respectively. For example: If both CTRL and ALT keys are pressed, the value of shift is 6.

illustrate

For both events, the focused object receives all keystrokes. A form can only gain focus if it has no visible and valid controls. Although the KeyDown() and KeyUp() events can be applied to most keys, they are most commonly applied to: extended character keys such as function keys, navigation keys, keyboard modifier keys and key combinations, distinguishing numeric keypads from regular numbers Key; when you need to respond to both pressing and releasing a key, you can use the KeyDown and KeyUp event procedures.

The KeyDown and KeyUp events cannot be referenced in the following situations: the form has a CommandButton control and the ENTER key when the Default property is set to True. The form has a CommandButton control, and when the Cancel property is set to True, the ESC key, TAB key, KeyDown and KeyUp use two parameters to interpret the uppercase and lowercase forms of each character: keycode - displays the physical key (replace A and a Returns as the same key) and shift-displays the status of the shift+key key and returns one of A or a.

If you need to test the shift parameter, you can use the shift constant defined in the parameter. This constant has the following values:

Constant value description

vbShiftMask 1 HIFT key bit

shield.

VbCtrlMask 2 CTRL key

bit mask.

VbAltMask 4 ALT key bits

shield.

This constant acts as a bit mask, which can be used to test any key combination.

Note: If the KeyPreview property is set to True, a form receives this event before the controls on the form. You can use the KeyPreview property to create global keyboard handling routines.

With the above knowledge, we can create a perfect program with shortcut keys. For example, in a program we need to use Ctrl+S to save, Shift to minimize, Alt+X and ESC to exit:

First start VB and select a new EXE file, pull a TextBox on the Form1 form, and set the KeyPreview property of Form1 to True, double-click Form1, select the KeyPress event of the Form, and enter the following code:

Private Sub Form_KeyPress(KeyAscii as Integer) 'Esc key to exit, VbEscape can be replaced by 27. If KeyAscii=VbEscape then End End Sub Enter the following code in the KeyDown event of Form: Private Sub Form_KeyDown(KeyCode as Integer,Shift as Integer) 'Processing Ctrl＋X,Shift,Alt＋X If Shift=2 And KeyCode=VbKeyS Then Print#FileNum,Form1.Text1.Text 'Ctrl+S save, VbKeyS=83 If shift=2 then Form1.WindowState=1 'Shift minimize If Shift=4 And KeyCode=VbKeyX Then End 'Alt+X exit, VbkeyX=88 End Sub in Enter the following code in the Load event of Form: Private Sub Form_load() Dim FileNum as integer FileNum=FreeFile Open App.Path+"Sample.txt" For Append As#FileNum End Sub