Transcript Visual Basic.net Windows Programming

Chapter 1
Mr. Wangler
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Visual Basic is used to create Windows,
Web, and command line applications.
An application makes the computer a useful
tool by enabling the user to perform a task,
such as word processing.
Buttons, check boxes, and text boxes are
common objects in a Windows application.
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Visual Basic language is an object oriented
programming language
Objects – appear on the screen (buttons,
check boxes, ….)
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Performing tasks with objects is the basis of
an OOP application.
A Windows application is event-driven.
Event-Driven application – executes code in
response to events.
Event – can occur when the user interacts
with an object, such as clicking a button.
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Project – contains all files required to
execute an application.
Design Window (Form) – displays the
application interface where objects are
added, deleted, and sized.
Toolbox – contains controls that are used to
create objects.
Solution Explorer Window – is used to
switch between the Design and Code
Window
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Properties Window – lists the properties of a
selected object.
Properties – defines its appearance, behavior,
position, and other attributes.
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A Windows application interface includes at
least one form.
A form is a graphical object that contains a
title bar, a system menu, and Minimize,
Maximize, and Close buttons.
A new Visual Basic Windows application
automatically includes on Form object.
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A Form object has properties just like a tool
that define its appearance, behavior, position,
and other attributes.
The Text property of a form defines what is
displayed in its title bar.
Pressing Enter or clicking outside the
Properties window applies the new Text
property value to the Form.
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The Toolbox in Visual Basic contains controls.
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Control – is used to add objects to a form.
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Control Objects – display information or get
user input.
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Name – identifies a control for the
programmer. It is good programming style
to begin Label object names with lbl.
Text – is the text displayed in the label.
Font – controls the font style and size of the
text.
Text Alignment – is the alignment of text in
a label.
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For most objects, the Name property should
always be set to a descriptive name. A proper
name begins with the appropriate prefix and
then describes the purpose of the object.
Following proper naming conventions is
GOOD PROGRAMMING STYLE.
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After the first time selecting Save from the
File menu or clicking on the Save button will
save your project.
An application should be saved frequently to
avoid losing changes.
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To run an application click the Start button
(Play button) on the toolbar or select Start
from the Debug menu.
To terminate a running application, click
the Stop Debugging button or select Stop
Debugging from the Debug menu.
Running an application means that a
program is first converted to a language the
computer understands in a process called
compiling.
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Prefix for Main Menu: mnu
Windows applications typically include menus
that contain commands.
A menu is modified in the Design window by
clicking a MenuItem object and typing a new
name.
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Applications contains sets of instructions
called program code.
Program Code – tells the computer how to
perform tasks.
Each line of code is called a statement.
In Visual Basic some code is automatically
generated for a form and the objects on the
form.
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Procedure - is a block of code written to
perform specific tasks.
Event Procedure – is a type of procedure that
performs tasks in response to user
interaction with an object.
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Assignment Statement – used in a procedure
to change a value at run time.
One use of assignment statements is to set
an object property at run time.
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Object.Property = Value
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Object = the control object name
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Property = the name of a property for that
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Value = is a valid property setting
object
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A dot(.) is required between Object and
Property to access the property.
The equal sign (=) assigns the property on
the left of the equal sign the value on the
rights of the equal sign.
Assignment Statements allow a single label to
display different text at run time.
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When a dot (.) is typed in a statement, an
AutoList of options is displayed.
The options displayed in an AutoList
depend on what was typed just before the
dot.
Me is used in the assignment statement so
that object names are displayed when a dot
is typed. Me refers to the Form object.
Selecting from an AutoList can reduce
typing errors in code. AutoList is also a
good way to choose values in an
assignment statement.
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A group of radio buttons is often used in an
application to enable the user to choose from
a set of options.
Name = prefix = rad
Text = text displayed next to the button
Checked = can be set to either True or False
to display the radio button as selected or not.
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Only one radio button in a group can be
checked at any given time. Therefore,
changing the Checked value of one button to
True automatically changes the other buttons
in the group to False.
The click event procedure executes when the
user clicks a button.
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A GroupBox is used to group related radio
buttons.
A GroupBox object must be added to a form
before adding RadioButton objects. Radio
buttons are then added to the group box by
clicking the RadioButton control and the
clicking the group box.
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Dragging a group box moves it and all the
controls within it together.
Name = prefix = grp
Text = is the text displayed at the top of the
group box.
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Comments are used to explain and clarify
program code for other programmers.
Comments have no effect on the way an
application runs.
The single quotation mar (‘) must begin a
comment. Anything after the single quotation
mark is considered a comment for that line of
the program only.
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Multiline comments can be created by placing
a quotation mark at the beginning of each
line.
Comments are good programming style and
should be used wherever code may be
confusing.
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Visual Basic.NET includes a set of built-in
arithmetic operators for:
Exponentiation (^)
Multiplication (*)
Division (/)
Addition (+)
Subtraction (-)
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Arithmetic operators are used to form a
numeric expression.
A numeric expression is not enclosed in
quotation marks because quotation marks
indicate text.
Since a label displays text, the value is
automatically converted to text.
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Visual Basic evaluates a numeric expression
using a specific order of operations, or
operator precedence.
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1. Exponentiation
2. Multiplication and Division
3. Addition and Subtraction
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Two operators of the same precedence, for
example + and -, are evaluated in order from
left to right.
The operators within parentheses are
evaluated first.
It is good programming style to include
parentheses when there is any confusion or
question about the numeric expression.
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The button is commonly used in Windows
application interfaces.
Name = prefix = btn
Text = is the text displayed on the button
A click event procedure is usually coded for a
Button object and executes when the user
clicks the button.