Unit II Basic VB

8/8/2019 Unit II Basic VB

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Understanding concepts in VB

The user interface is the link between the user and the application. The

usability of the application depends on the interface. While creating anapplication in VB, the form is the basic element of the user interface.

Controls are then added to provide specific functionality. Both these

objects can be modified by the programmer by changing their

properties, methods and events.


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Designing the interface

To Draw a Control on a form

To remove a control from the form

To move / resize a control

Aligning controls

Container control / child control


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Naming Controls

The names of controls and forms must satisfy the following

criteria: It must begin with a letter.

must contain only letters, numbers and underscore character(

_ ).

Punctuation characters and spaces are not allowed.

must not be longer than 40 characters.


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Which of the following are valid object names:

Name

Lbx12

@Rs

_lb1

123_label

?1

Star1

%age

Valid / Invalid

Valid

Invalid

Invalid

Invalid

Invalid

Valid

Invalid


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We can use a prefix to describe a class, followed by a

descriptive name for the control. Using this naming

convention makes the code more self-descriptive and

alphabetically groups similar objects in the object list box.

E.g. we can name a checkbox control as ChkReadOnly


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Control Prefix

Label Lbl

Frame Fra

Chekbox chk

Combobox Cbo

Hscrollbar Hsb

Timer Tmr DirListBox Dir

Shape Shp


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Control Prefix

Image Img

Line Lin

PictureBox Pic

TextBox Txt

CommandButton Cmd

OptionButton Opt

ListBox Lst


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Properties

Properties are the object attributes. The controls / objects that

we draw on a form, have some properties associated with

them. After a control is added to a form, the programmer can

set the characteristics of the controls and the form such as

size color, screen location or the state of the control, such as

enabled or disabled.


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A few common properties are :

Name

Appearance

Backcolor

Forecolor Font

Caption

Width

Height

Left

Top Enabled

Visible


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Working with Forms

In VB, the Form acts as the container for all the controls that

make up the interface. The form is the top-level object in a VBapplication, and every application starts with the Form.


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Characteristics of a form:

y Title bar: on which the forms caption is displayed.

y Control menu: On left end of the title bar is the control menu icon.Clicking this icon opens the control menu. The control menucontains the following commands:

1. Restore

2. Move

3. Size4. Minimize

5. Maximize

6. Close


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On the right side of the title bars are the three buttons:

1. Minimize

2. maximize3. close buttons

Clicking these buttons perform the associated function.


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Customizing form properties:

Property Description

MinButton Specifies whether a minimize window button appears on

the form.

MaxButton Specifies whether a maximize window button appears on

the form.

Controlbox This property displays the control menu, if it is set to true.

By default it is true. We can set it to false to hide the

control menu icon and disable the control menu.When the controlbox property is set to false the three

buttons (Minimize, Maximize and close) on the title bar

also gets disabled.


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Borderstyle This property determines the borders style for a Form

and also its appearance. It can take any of the

following values:Value Description

0-None No border for form. Form

cannot be resized. This

setting should be avoided.

1-Fixed Single Visible border. Form cannot be

resized.

2- Sizeable Visible border. Form can be

moved and resized.


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Value Description

3- Fixed dialog For fixed dialog boxes

4- Fixed tool window Form has a closed button

only; cant be sized.

5- Sizeable Tool Window Same as the fixed tool /

window, but the Form can

be resized.


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Backcolor Specifies the forms background color.

Enabled Determines whether the form is active.

Font Produces a font dialog box in which we can set the

texts font name, style and size

Icon Describes the icon graphic image displayed on the

taskbar when the user minimizes the form

Moveable Specifies whether the user can move the form at

runtime.

Picture Determines the graphic image that appears on the

forms background at runtime.


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Setting the startup form

An application generally has more than one form. When an

application starts, the main form that gets loaded first of all iscalled Startup form.

By default, the first form in the application is designated as the

start up form. If we want a different form to display when the

application starts, we must change the startup form.


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To change the startup form

1. From the project menu, choose Project properties.

2. Choose general tab3. In start up object list box, select the form we want as the new

startup form.

4. Choose OK.


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Loading ,Showing and Hiding forms

A form can be in one of the following states:

(i) Not loaded : Form lives on the disk file and doesnt take upany resources ( such as memory etc.)

(ii) Loaded and hidden: Form is loaded into memory and is

ready to be displayed.

(iii) Loaded and shown : Form is shown and the user can

interact with it.


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State of a form can be changed by using Load, Unload, show

and Hide methods.

Loading ,Unloading forms

Load

Unload


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The load method does not display the form on the desktop, it

just loads the form in the memory.

The unload method removes a form from the memory and the

resources occupied by it are released so that they can be

used by other applications


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Showing Forms

Syntax

< formname>.show []

The argument can take one of the following values:

0 Modeless (Default) allows the user to switch to any

other form of the application

1 Modal A modal form takes control of

the application and does not letthe user work with other parts

of the application unless this

form is closed.


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Note : The Show method also loads the form if it is not

loaded already.

Hiding forms

.hide

A hidden form remains in memory and can be displayed instantly

with show method.


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Label Control

A label control displays text that user cannot directly change. The

actual text displayed in a label is controlled by its caption property.

MajorProperties of Label control are:

y 1. Caption - the propery used to display text in the label control

y 2. Font the property used to specify the display font, style and size

for the caption of the label

y 3. BackColorand ForeColor- colors of the background and the text


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y 4. BackStyle - Opaque or Transparent - whether the background isvisible or not

y 5. Name the property used to name the label control.

y 6. Alignment specifies the alignment of labels caption. Alignment

can be left justified, right justified or centered.


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y 7. Wordwrap this property is used to set the word wrapping option

for the caption text. By default, if the text exceeds the width of the

label, the text wraps to the next line. If the text goes beyond the

height of label, then it is clipped. If we set this property to True then

the text is wrapped and expanded vertically.

y 8. Autosize this property causes the control to horizontally expand

and adjust to the size of its contents

y 9. Borderstyle- this property, if set to 1, the label appears with a

border.


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Textbox Control

Textboxes are versatile controls that can be used to get input fromthe user or to display text.

Major properties of a textbox control are:

1. Name: property to specify name

2. Text : property to specify text to be displayed in the textbox.This text can be accessed as well as edited.

3. Font the property used to specify the display font, style and size forthe caption of the label


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4. Maxlength: property used to set the maximum number of charactersallowed in the textbox

Note : The amount of text that can be placed in a multiline Textboxcontrol is limited approximately to 32 KB. A single line textbox can

hold only 255 characters.

5. Enabled : this property is used to set a value that determines if thetext box can respond to the events that are generated by the user

6.Multiline: this property, allows multiple lines of text in the text box.

7. Scrollbar: this property allows us to attach a built in scrollbar to thetextbox, so that the user can scroll text in the textbox, when theprogram is running.


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8. PasswordCharacter: This property is important if we plan to

read a password through textbox. If we specify a character in

this property, then in place of the text being entered, these

characters are displayed.

9. Seltext: property that returns the selected text.

10. Selstart: property that returns or sets the position of the first

character of the selected text.

11. SelLength: property that returns the length of the selected

text.


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BackColor

Sets the colour of the CommandButton's background. This

property only takes effect when the Style property is set to 1 -

Graphical.

Cancel

If this property is set to True, pressing the Escape key at runtime

will activate the CommandButton's Click event. Only one

CommandButton on the Form can have this property set to

True.


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Default

This property determines if the command button responds to an

Enter keypress even if another control has the focus. The

CommandButton, which has this property set to True, will also

appear with a darker border.

Enabled

When this property is set to False, the user is not able to interact

with the CommandButton in any way e.g. it cannot be clickedon or have focus. The caption will appear greyed out.


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Font

In design time, this brings up the Font dialog box to allow us to

choose the font name, style, size and whether the Strikeout

and Underline attributes are set.

Height

Sets the height of the CommandButton.

Left

Sets the X coordinate of the CommandButton.


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Top

Sets the Y coordinate of the CommandButton.

VisibleDetermines whether the CommandButton appears on the

Form. I.e. if set to False, the CommandButton will be

unavailable to the user - even by trying to set focus to it with

the tab key.

Width

Sets the width of the CommandButton.


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Picture

Sets the picture, which is displayed in the background of the

CommandButton. The Style property needs to be set to 1 -

Graphical for this property to work.

Style

This needs to be set to 1 - Graphical if you want to use the

graphical properties of the CommandButton (apart from

Fonts).


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TabIndex

Sets the order in which the controls will get focus when the tab

key is pressed. The control that has 0 as its TabIndex will have

focus when the Form is loaded.

TabStop

If you set this to False, the CommandButton will not get focus

when the tab key is pressed.

Tag

This property can be set to a string if you need to store any extra

information related to the CommandButton.


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ToolTipText

When this property is set, the text will popup over the

CommandButton when the user hovers the mouse pointer over

it. This can be useful if we cannot fit all the text you need to in

the Caption.


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Assigning access keys

To assign a keyboard access key to a command button, we need

to place an ampersand (&) in front of the letter that is to be

used as access key, while setting the caption property of

command button.

For example, if we want to assign Alt + P as the access key for a

print command button, we can set the caption property to&Print. VB shows this key by underlining it i.e. this caption

appears as Print.


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Frame control

A frame control is used to group various controls. A frame

control is a container control , i.e. it contains other controls

in it. It does not carry out any job / action by itself , it does not

respond to any events by itself.


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Major properties of frame control

Caption

P

roperty to display text in the frame control

Font

Property to set font, style, and size of captioned text of frame

(Name)

property to name the frame


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Visible

Property used to set a value indicating whether the frame should bevisible ( value True) or not (value false)

BorderstyleProperty used to specify the style of border.

0- None

1- Fixed single

Appearance

Property used to set look of the frame

0 Flat

1- 3D


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OptionButton Control (Radio Button)

The option buttons are used to offer a small set of options from

which a user can choose one.

Option buttons should always work as part of a group; selecting

one option button immediately clears all the other

buttons in the group.

Option button groups operate in a container control, such as aframe. Therefore, different sets of option button groups should

be placed in their own frame on the form.


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Major properties of option button control are :

Caption

P

roperty to display text for option button

Name

Property to name the option button

Value

Property to set the state of option button. If set to True, the

option button appears selected.


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Alignment

Property to set the alignment of the option button.

0- Left justify option button appears on the left of caption

1-Right justify option button appears on the right of thecaption.

Style

This property is used to set the appearance style which can either be 0-standard (default) or1- graphical ( it makes option button appearas a command button.


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Enabled

Property used to set a value that determines whether a

checkbox can respond to user-generated events


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Checkbox control

The checkbox controls are used for offering a small set of

choices from which a user can choose one or more options.

A check box indicates whether a particular condition is on or off.

Checkboxes work independently of each other, a user

can select any number of checkboxes at the same time.


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Major properties of checkbox control are :

Caption

Property the specify text to be displayed.

Name

Property to specify name

Alignment

Property to set the alignment of the checkbox.0- Left justify checkbox appears on the left of caption

1-Right justify checkbox appears on the right of thecaption.


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Enabled

Property used to set a value that determines whether a

checkbox can respond to user-generated events

Value

Property used to specify the state of checkbox. If its value is :

0 or Unchecked , it means the checkbox is unchecked

1 or Vbchecked it means the checkbox is checked

2 or Vbgrayed it means the checkbox is disabled

.


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ListBox Control

The listbox control presents a list of choices to the user. The

choices are presented in one or more columns. If the number

of items exceeds what can be displayed in a list box,

scrollbars automatically appear on the control.


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Major properties of listbox control are :

Multiselect : This property determines whether the user can select

the lists multiple items or not. This property must be set at design

time. At runtime we cant change this property, we can only read itsvalue.

It can take following values:

0 multiple selection not allowed, default setting1 Simple multiple selection (mouse click, pressing space bar)

2 Extended multiple selection (Shift key + mouse click/ Ctrl + mouse

click)


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Sorted this property determines whether the items inthe list is sorted or not.

( Value True / False)

Style 0 Standard appearance

1 Checkbox appearance

Listindex Gives the index of selected item in the list. I fmultiple items are selected, then listindexproperty stores the index of most recentlyselected items.


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Newindex this property returns the index of the item most

recently added to the listbox


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Adding items to list at runtime

Syntax

.Additem ,

Deleting items from the list

Syntax

.Removeitem


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Clearing the List

.Clear

Accessing items in the list

.list()

Counting the number of items in list

.listcount


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Combo Box

It combines the features of a listbox and a textbox.

Combo box is similar to a listbox control it contains multiple

items of which the user may select one, but it takes less

space on screen.

It is an expandable listbox control, which can grow when theuser wants to make a selection and retract after the selection

is made.


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Hscrollbar and Vscrollbar controls

A scrollbar is a long stripe with an indicator that lets the user select avalue between the two ends of a control.

The scrollbar comes in two forms :

a) Horizontal scrollbar HScrollbar

b) Vertical Scrollbar VScrollbar

The only difference between the two is their orientation. The left end (in a horizontal scroll bar) and the top end ( in a vertical scroll bar)corresponds to its minimum value and the other end corresponds toits maximum value.


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The current value of the scrollbar control is determined by the

position of the indicator ( or scrollbox) which is scrolled

between the minimum and the maximum values.

The basic properties are:

Min this property returns the scrollbars minimum

value

Max this property returns the scrollbars maximum

value


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value this property returns the current value of

scrollbar

Largechange specifies the change in value if user clicks on

the scrollbar in an area other than the indicatorand the arrow keys

Smallchange specifies the change in value if the user clicks at

the arrow keys of the scrollbar.


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The scroll bar controls use the Scroll and Change events to

monitor the movement of the scroll box along the scroll bar.

Event Description

Change occurs after the scroll box is moved

Scroll occurs as the scroll box is moved. Does

not occur if the scroll arrows or scrollbar


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Image Control

Image control is used to display graphics. Image control can

display graphics in the following formats: bitmaps (BMP),

device independent bitmaps (DIB), metafiles (WMF),enhanced metafiles (EMF), GIF and JPEG files, and icons

(ICO) and cursor( CUR) files.

Image controls can be used as a substitute for command buttonsas items in a toolbar.


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Some properties of image control

Appearance 0 Flat

1 3D . We can view the result of this property

if we set a border to the image control.

Borderstyle 0 None

1 Fixed Single

Picture this property determines which picture is

displayed in the image box.


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Loading graphics into Imagebox Control

Pictures can be loaded into the imagebox control at design time

by selecting the Picture property.

If we want to load or change image at runtime, we can do this by

using the picture property and the Loadpicture function.

E.g.

Image1.Picture= Loadpicture(c:\images\fountain.gif)


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To clear the graphics from the image control, we set the picture

property to Nothing;

Image1.Picture= Nothing

Or use the loadpicture function without specifying the file name:

Image1.Picture=Loadpicture


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Picturebox control

The picture control is used to display graphics, to act as

container for other controls and display output from graphics

methods or text using the print statement.

Picturebox control is similar to the image control in that each can

be used to display graphics in the application and each

supports the same file formats. The picture box control ,contains additional functionality which the image control does

not for example the ability to act as a container for other

controls and support for graphics methods.


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Picture box control can display graphics in the following formats:

bitmaps (BMP), device independent bitmaps (DIB), metafiles

(WMF), enhanced metafiles (EMF), GIF and JPEG files, and

icons (ICO) and cursor( CUR) files.


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Some properties of picture box control

Appearance 0 Flat

1 3D . We can view the result of this property

if we set a border to the picture box

control.

Borderstyle 0 None

1 Fixed Single

Picture this property determines which picture is

displayed in the picture box.


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Autosize this property determines whether picture box is

automatically resized to display its image

entirely.

True Control is resized to the dimensions ofthe image it conatins.

False Only the part of the image that can fit in

the control is displayed


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Loading graphics into Picture box Control

Pictures can be loaded into the picture box control at design time

by selecting the Picture property.

If we want to load or change picture at runtime, we can do this

by using the picture property and the Loadpicture function.

E.g.

picture 1.Picture= Loadpicture(c:\images\fountain.gif)


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To clear the graphics from the picture control, we set the picture

property to Nothing;

picture 1.Picture= Nothing

Or use the loadpicture function without specifying the file name:

picture 1.Picture=Loadpicture


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Difference between Image box control and picture box control

Image box control is used only to display graphics.

Picture box control can be used to display graphics and can also beused as a container control. It also provides support for graphics

properties and methods. Picture Box controls support all the

properties related to graphic output, including AutoRedraw,

ClipControls, HasDC, FontTransparent, CurrentX, CurrentY, and all

the Drawxxxx, Fillxxxx, and Scalexxxx properties.P

ictureBoxcontrols also support all graphic methods, such as Cls, PSet, Point,

Line, and Circle and conversion methods, such as ScaleX, ScaleY,

TextWidth, and TextHeight.


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The sizing behavior of the image control differs from that of

picture box control. It has the Stretch property while the

picture box has as Autosize property.

Stretch property of Image box

this property determines whether the image is resized if the sizeof the imagebox control is different from the picture loaded into

it.

True: image is resized to fill the area of imagebox control.

false: Imagebox control behaves like a picture box control with

Autosize property set to true.


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Autosize Property of picture box

this property determines whether picture box is automatically

resized to display its image entirely.

True Control is resized to the dimensions of the image it

conatins.

False Only the part of the image that can fit in the control isdisplayed


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The image box control is good for displaying graphics and uses

fewer resources than picturebox controls. The picture box

control provides methods for drawing at runtime and is much

more flexible than image box control.


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Timer Control

The Timer control allows you to perform a task at a specified

interval or to wait for a specified length of time.

Following are the facts about Timer control:

It is not visible to the user at run-time

The actions that you want to happen at the specified interval

are coded in the Timer's Timerevent.


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We specify the interval at which we want actions to occur, in

the Timer control's Interval property. The value is specified in

milliseconds (1000 milliseconds = 1 second). The timer

control triggers a timer event after each interval of time goes

by.

The interval property contains a value that must range from 1to

65535.


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We turn the timer "on" or "off" by setting its Enabled property

to True or False, respectively. The Enabled property is set to

True by default. Also setting the interval property to 0 disables

the timer control.


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Program for Blinking text

The Timer control can be used to make an object on your screenappear to blink. This is done by toggling the Visible property

of the object on and off at short intervals. The Visible propertyis available to nearly all controls. It is a Boolean property thatdetermines whether or not the control is visible to the user atrun time by setting its value to True or False To build a simpledemo, perform the following steps.

Start a new VB project.

Place a label on the form and name it lblProcess. Set its Captionto Processing . . ..


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Set it to a large font and set its Forecolor property to the color of

your choice. Center it on your form.

Place a timer on the form and name it tmrBlink. Set its Interval

property to 250.

In the tmrBlink_Timerevent, place the following single line ofcode:

lblProcess.Visible = Not lblProcess.Visible

Run the project. The label will blink

Unit II Basic VB

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