Visual Basic.NET How to Program (PDF)

508 Graphical User Interface Concepts: Part 1 Chapter 12
12.8 PictureBoxes
A picture box (class PictureBox) displays an image. The image, set by an object of class
Image, can be in a bitmap, a GIF (Graphics Interchange Format), a JPEG (Joint Photographic
Expert Group), icon or metafile format. (Images and multimedia are discussed in
Chapter 16, Graphics and Multimedia.)
The Image property specifies the image that is displayed, and the SizeMode property
indicates how the image is displayed (Normal, StretchImage, Autosize or Center-
Image). Figure 12.27 describes important properties and events of class PictureBox.
The program in Fig. 12.28 uses PictureBox picImage to display one of three
bitmap images—image0, image1 or image2. These images are located in the directory
images (in the bin/images directory of our project), where the executable file is also
located. Whenever a user clicks picImage, the image changes. The Label
(named lblPrompt) at the top of the form displays the text Click On Picture Box to
View Images.
PictureBox
properties and events Description / Delegate and Event Arguments
Common Properties
Image Sets the image to display in the PictureBox.
SizeMode Enumeration that controls image sizing and positioning. Values are
Normal (default), StretchImage, AutoSize and CenterImage.
Normal places image in top-left corner of PictureBox, and
CenterImage puts image in middle (both truncate image if it is too
large). StretchImage resizes image to fit in PictureBox.
AutoSize resizes PictureBox to hold image.
Common Events (Delegate EventHandler, event arguments EventArgs)
Click Generated when user clicks the control. Default event when this control
is double clicked in the designer.
Fig. 12.27 PictureBox properties and events.
1 ' Fig. 12.28: PictureBoxTest.vb
2 ' Using a PictureBox to display images.
3
4 Imports System.IO
5 Imports System.Windows.Forms
6
7 Public Class FrmPictureBox
8 Inherits Form
9
10 Private imageNumber As Integer = -1
11
12 ' instructions display label
13 Friend WithEvents lblPrompt As Label
Fig. 12.28 Using a PictureBox to display images (part 1 of 2).