Visual Basic.NET How to Program (PDF)

514 Graphical User Interface Concepts: Part 1 Chapter 12
Keyboard Events, Delegates and Event Arguments
Handled Indicates whether the event was handled.
KeyCode Returns the key code for the key as a Keys enumeration.
This does not include modifier-key information.
Used to test for a specific key.
KeyData Returns the key code for a key as a Keys enumeration,
combined with modifier information. Contains
all information about the pressed key.
KeyValue Returns the key code as an Integer, rather than as a
Keys enumeration. Used to obtain a numeric representation
of the pressed key.
Modifiers Returns a Keys enumeration for any modifier keys
pressed (Alt, Control and Shift). Used to determine
modifier-key information only.
Fig. 12.31 Keyboard events, delegates and event arguments (part 2 of 2).
Figure 12.32 demonstrates the use of the key-event handlers to display a key pressed
by a user. The program is a form with two Labels. It displays the pressed key on one
Label and modifier information on the other.
Initially, the two Labels (lblCharacter and lblInformation) are empty. The
lblCharacter label displays the character value of the key pressed, whereas lblInformation
displays information relating to the pressed key. Because the KeyDown and
KeyPress events convey different information, the form (FrmKeyDemo) handles both.
The KeyPress event handler (lines 18–23) accesses the KeyChar property of the
KeyPressEventArgs object. This returns the pressed key as a Char and displays the
result in lblCharacter (line 22). If the pressed key is not an ASCII character, then the
KeyPress event will not fire, and lblCharacter remains empty. ASCII is a common
encoding format for letters, numbers, punctuation marks and other characters. It does not support
keys such as the function keys (like F1) or the modifier keys (Alt, Control and Shift).
1 ' Fig. 12.32: KeyDemo.vb
2 ' Displaying information about a user-pressed key.
3
4 Imports System.Windows.Forms
5
6 Public Class FrmKeyDemo
7 Inherits Form
8
9 ' KeyPressEventArgs display label
10 Friend WithEvents lblCharacter As Label
11
12 ' KeyEventArgs display label
13 Friend WithEvents lblInformation As Label
14
Fig. 12.32 Demonstrating keyboard events (part 1 of 3).