2 form and controls 1

8/3/2019 2 Form and Controls 1

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Part 1 : Forms and Controls

F5227VB.NET PROGRAMMING

TOPIC 2


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VB.NET Controls

Navigate IDE

A Text Box Walkthrough

A Button Walkthrough

A Label Walkthrough

A List Box Walkthrough

The Name Property

A Help Walkthrough Fonts / Auto Hide


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Starting a New Project

Default: Windows

Application


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The Integrated Development Environment

(IDE)

Menu bar provides many menu items

Examples include File and Edit menus

Toolbar lies below menu bar

Provides shortcuts to the menu bar

Toolbox

Contains various icons representing VB controls

Solution Explorer Shows all forms, references, classes, and modules the

current project contains


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The IDE

Menu bar

Blank form

in IDE

Toolbox Toolbar


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Solution Explorer and Properties Window

Solutions Explorer

shows all the forms,

references, classes,

and modules in theproject

Properties window

shows all the

properties of the

selected object


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The Code Window

Tabs at top let you toggle between the form and

the code window

Comments

appear green

in the IDE

Object-oriented syntax:

object and property

separated by dot (period)

Procedure box

lists events

the object inthe object box

recognizes

Object boxlists all

objects in

the form


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Understanding the IDE

Design time

When you are placing controls on the form

When you are writing code in the code window

RuntimeWhen the code in your project comes to life,

responding to events Press Start on the Debug menu in the IDE

Press the F5 key in the IDE Press the start button in the IDE


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Interfaces of VB Objects

Forms and controls are objects

Objects have interfaces:

1) Properties: typically relate to appearance of

objects2) Events: user or system actions recognized by

the object Procedures written to handle events

3) Methods: actions that objects are capable ofperforming


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1) Properties

Special types of data associated with object

Most relate to appearance of objects

i.e. Label1.BackColor = Color.Red

Some relate to behavior of objects

i.e. btnNext.Enabled True

Object and property separated by dot

(period) Property must be given a value


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2) Events

User or system actions the object recognizes

i.e. a button has a Click event

Event procedure

Procedure written to handle a specific eventAlso called event handler

Syntax: Private Sub ObjectName_Event

Code surrounded by Sub End Sub

Private refers to the scope of the procedure

Object and event separated by underscore


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3) Methods

Actions objects are capable of performing

i.e. Me.Close()

Syntax: Object.Method(Parameter List)

Parameter list: arguments passed in to the

method

Parameter list must be enclosed in parentheses,

even if no parameters are required


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A Text Box Walkthrough

Drag Text Box from ToolBox

Sizing

Delete

Properties

Text, Color, Font, Size, Location, Visible,

Enabled


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A Button Walkthrough

Add the button

Change the Text property


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A Label Walkthrough

Add the Label

Change the Text property

Resize the control


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A List Box Walkthrough

Add the List Box

Add data

Resize the control


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The Name Property

How the programmer refers to a control in code

Name must begin with a letter

Must be less than 215 characters long

May include numbers and the underscore

Naming convention: use appropriate 3 character

naming prefix

First three letters identifies the type of control Remaining letters identifies the purpose

E.g. a text box to store a social security number would be

called txtSocialSecurity


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Common Control Name Prefixes

Control Prefix Examplebutton btn btnComputeTotallabel lbl lblInstructionslist box lst lstOutputtext box txt txtAddress


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Fonts

Proportional width fonts take up less space

for "I" than for "W" like Microsoft Sans Serif

Fixed-width fonts take up the same amount

of space for each character like CourierNew

Fixed-width fonts are good for tables


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Auto Hide

Hides tool windows when not in use

Vertical push pin icon indicates auto hide is

disabled

Click the push pin to make it horizontal andenable auto hide


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Viewing the Code

The GUI Forms Designer generates textual

code

Prior to VB programmers wrote everything in

textual code Click on the Form1.VB tab to see the code

(not the design tab)


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An Event Procedure Walkthrough

An event is an action, such as:

The user clicks on a button

A form is minimized

The mouse enters or exits a control

The form is re-drawn

Usually, nothing happens until an event

occurs

Th th t i ti


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The three steps in creating a

VB.NET program:

1. Create the interface; that is, generate,

position, and size the objects.

2. Set properties; that is, configure the

appearance of the objects.3. Write the code that executes when events

occur.


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Changing Properties

Properties are changed in code with the following:

controlName.property = setting

This is an assignment statement

Examples:txtBox.ForeColor = Color.Red

txtName.Text = "Hello There"

txtName.Visible = False

txtName.Location.X = 100


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Adding Code to an Event

To add code for an event: In the VB Code Window select the control on the left side

menu and the event of interest on the right side menu

Or double-click the control in the designer to bring up themost common event for that control

Other methods for opening the Code window: If the Code window is visible, click on it

Double-click anywhere on the Form window Select the Code option from the View menu

Press the F7 method key anywhere on the design form

Select the View Code icon from the Project Window


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Program Region


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Event Procedures

Private Sub objectName_event(ByVal senderAs

System.Object, ByVal eAs System.EventArgs)

Handles objectName.event

For now you can ignore most of this, aside from knowing thename of the subroutine:

Private Sub objectName_event() Handles

objectName.event


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Structure of an Event Procedure

Private Sub objectName_event(...)

Handles objectName.event

statements Your code goes hereEnd Sub


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IntelliSense

Automatically pops up to give the programmer

help.


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Code for Walkthrough

Private Sub txtFirst_TextChanged(...)

Handles txtFirst.TextChanged

txtFirst.ForeColor = Color.Blue

End Sub

Private SubbtnRed_Click(...)

Handles btnRed.Click

txtFirst.ForeColor = Color.Red

End Sub

Private Sub txtFirst_Leave(...)

Handles txtFirst.Leave

txtFirst.ForeColor = Color.Black

End Sub


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Assigning properties in code

The following won't work:

Form1.Text = "Demonstration"

The current form is referred to by the

keyword Me.

Me.Text = "Demonstration"

The Declaration Statement of an


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The Declaration Statement of an

Event Procedure

A declaration statement for an event procedure:

Private Sub btnOne_Click(...) HandlesbtnOne.Click

The name can be changed at will. For examplePrivate Sub ButtonPushed(...) HandlesbtnOne.Click

Handling more than one event:Private Sub ButtonPushed(...) HandlesbtnOne.Click, btnTwo.Click


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The MessageBox.Show Method

The MessageBox.Show method is used to display a boxwith a message for the user

The message box also contains a title and an icon

General forms of the MessageBox.Show method

MessageBox.Show(text) MessageBox.Show(text, caption)

MessageBox.Show(text, caption, buttons)

MessageBox.Show(text, caption, buttons, icon)

MessageBox.Show(text, caption, buttons, icon, defaultbutton)

To do: Add a MessageBox.Show to the button clickevent


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Console.WriteLine

Another handy way to output information is to the Console:

Console.WriteLine("Hello there")

Outputs the message in double quotes and adds a

newline

Console.Write("Hello again. ")

Outputs the message in double quotes without a

newline

Useful for debugging, dont have to push the OK button and

clutter up the screen with message boxes

Adding Additional Event


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Adding Additional Event

Procedures

Comments

Explanatory remarks made within a program

Indicated by an apostrophe () or the keyword Rem

Statement categories An executable statement causes some specific action

to be performed by the compiler or interpreter

A nonexecutable statement is a statement that

describes some feature of either the program or itsdata but does not cause the computer to perform

any action


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Focus on Program Design and Implementation:

Creating a Menu of Forms

A main menu form can be displayed as an

applications opening window to provide the

user with a summary of what the applicationcan do

The main menu form is created as either:

A set of buttons A menu bar


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A Sample Main Menu Screen

Focus on Program Design and Implementation:

Creating a Menu of Forms


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Adding a Second Form

From the Project menu, select Add New Item, and then WindowsForm Default name is Form2.vb

To display a form:Dim varName As New FormNamevarName.Show()

E.g.:Dim secondForm as New Form2secondForm.Show()

To make the current form invisible but retain its variables andcomponents:

Me.Hide() (could display again with Show())

To destroy a form and unload its variables and components:Me.Close() (need to create a new one to display again)


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Knowing About: The Help Facility

Visual Basics Help Facility can be accessed byselecting either the Contents, Search, orIndex options from the Help menu

The Contents tab displays a Table of Contentsfor the documentation

The Index tab provides both a general indexof topics and a text box for user entry of a

specific topic The Search tab provides a means of entering

a search word or phrase


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Getting Help from the Help Menu

Enter search

term in the

Look for box

Double-click

an item in

the list box

Double-click an item in the lower center pane; upper center pane

shows results



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(Continued)

Dynamic Help

The Dynamic Help window displays a list of help

topics that changes as you perform operations

To open the Dynamic Help window, click Help onthe menu bar and then click Dynamic Help

Context-sensitive Help

Context-sensitive Help immediately displays a

relevant article for a topic

To use this facility, select an object and press F1

Common Programming Errors and


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Common Programming Errors andProblems

A common problem is not being able to locate

all of the elements needed to create an

application

Can usually get these windows back from theView menu

A common error is forgetting to save a

project at periodic intervals at design time


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Summary

Event-based programs execute program codedepending on what events occur, whichdepends on what the user does

GUIs are graphical user interfaces that

provide the user with objects that recognizeevents

The term design time refers to the periodof time when a Visual Basic application is

being developed under control of Visual Basic The term run time refers to the period of

time when an application is executing


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Summary

A Visual Basic program consists of a visual partand a language part

Basic steps for developing a Visual Basicprogram:

Create the GUI Set the properties of each object on the interface

Write procedural code

A form is used during design time to create agraphical user interface for a Visual Basicapplication

The most commonly placed objects on a form arebuttons, labels, and text boxes

2 form and controls 1

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