ppt lesson 03

Microsoft Visual Basic 2005 BASICS

Lesson 3

Events and Code

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Objectives

Describe events and how events are key to Windows programs.

Access the Code window. Add code to a command button. Add a picture to a form.

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Objectives (cont.)

Set picture properties. Use code to set properties. Set the Cancel and Default command

button properties. Create a stand-alone Windows program.

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Events

Event-driven system Computer is constantly waiting for the user

to take some action With the mouse, keyboard, or other device

Action triggers an event Software in the computer attempts to find

something to do with that action

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Events (cont.)

When you create an object It is up to you to write the code that will

handle the events. Event procedure

Code that handles a specific event

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Accessing the Code Window

Add code to a command button Open the form that contains the command

button. Double-click the command button.

The Code window will appear.

Subroutine Section of code to perform a specific task

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Accessing the Code Window (cont.)

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Adding Code to a Command Button

Add code to the Code window Simply enter the code from the keyboard.

You can insert and delete text and use cut, copy, and paste.

IntelliSense technology Anticipates what you are about to key

Completes your statement for you

Visual Basic is not case sensitive.

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Adding Code to a Command Button (cont.)

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Adding a Picture to a Form

PictureBox control Provides a framework for displaying a

picture on a form

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Adding a Picture to a Form (cont.)

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Adding a Picture to a Form (cont.)

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Adding a Picture to a Form (cont.)

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Adding a Picture to a Form (cont.)

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Setting Image Properties

Image controls Have an extensive set of properties that

can be changed

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The Name Property

Name property Names the PictureBox control

The pic prefix is often used when naming PictureBox controls.

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The SizeMode Property

SizeMode property Allows you to specify what to do when

picture and space available do not match Values

Normal Center StretchImage AutoSize

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The SizeMode Property (cont.)

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The SizeMode Property (cont.)

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The Visible Property

Visible property Gives you

control over when a picture is visible to the user

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Use Code to Set Properties

Change a property by specifying Name of the control Property Value

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Use Code to Set Properties (cont.)

The item to the right of the dot is called a method.

In object-oriented programming You do not actually set the property. You ask an object to set its own property

by sending it a message.

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Use Code to Set Properties (cont.)

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Use Code to Set Properties (cont.)

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Adding Access Keys to Command Buttons

Access key Declared in the Text property in Visual

Basic programs Allows a user to activate a command

without using a mouse

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Setting the AcceptButton and CancelButton Form Properties

AcceptButton property Names the command button to be used

when the user presses the Enter key CancelButton property

Names the command button to be used when the user presses the Esc key

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Summary

Windows is an event-driven environment. In an event-driven system, the user triggers events that control the work.

To control what happens when an event occurs, you must write event procedures for each event that you want to handle.

To access the Code window, double-click an object, such as a command button.

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Summary (cont.)

Visual Basic code is written in sections called subroutines.

Adding code is much like working in a word processor. The basic text-editing features are available. In addition, Visual Studio 2005 has IntelliSense features to help format your program code.

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Summary (cont.)

The End statement ends a program. The PictureBox tool allows you to add a

PictureBox control to a form. Using the (Name) property, you can give

a PictureBox control a name. That name will be used when you refer to the control in code.

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Summary (cont.)

Setting the SizeMode property to StretchImage causes a picture to resize to fit the dimensions of the PictureBox control. Setting the SizeMode property to AutoSize causes a PictureBox control to resize to fit the picture loaded into it.

The Visible property controls whether an object is shown or hidden.

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Summary (cont.)

Setting properties in code is one of the most common uses for Visual Basic code. Setting properties in code allows you to change properties while a program runs.

A command button with an ampersand (&) in front of a letter in the Text property causes that letter to become an access key.

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Summary (cont.)

The command button named in the form’s AcceptButton property will be activated when the user presses the Enter key. The command button named in the form’s CancelButton property will be activated when the user presses the Esc key.