Copyright (c) 2003 by Prentice Hall Provided By: Qasim Al- ajmi Chapter 3 Some Visual Basic Controls and Events Visual Basic. NET

Copyright (c) 2003 by Prentice Hall Provided By: Qasim Al-ajmi

Chapter 3Some Visual Basic Controls and

Events

Visual Basic. NET


Objectives

Have a clear understanding of the important features and the role various controls play in the user interface for data-entry operations

Set the tab order for the controls placed on the form

Understand the nature and uses of various events


Obtaining Open-Ended Input

Text box– Has a Text property– Should have a label giving a clue what goes in the box

Masked Edit Box– Has a Mask property

Mask can contain placeholders (#,A) or literals (-,())– Has a Text property

The exact content of the box, including literals– Has a ClipText property

Content of the box, without literals


Focus

Control must have focus to accept data input– Press Tab key until you get to the control– Click on the control– By code, using the Focus method

Focus method should be part of button click events or error handling procedures

When a text box gets focus, a blinking cursor appears in box

Enter event is triggered when a control receives focus


Comparing Text Properties

Setting at design time– Can only be done with text box

Setting at runtime– With text box, can set to anything– With masked edit, text must match mask pattern

Clearing at runtime– With text box, set to zero-length string– 3 steps for masked edit:

Clear the mask Set text to zero-length string Redefine the mask


Highlighting Text

SelectedText property of text box gives the text that is highlighted

– Corresponding property for masked edit: SelText SelectionStart property of text box gives the position

where highlight begins– Corresponding property for masked edit: SelStart

SelectionLength property of text box gives the length of highlighted text

– Corresponding property for masked edit: SelLength


Highlighting the Text

Len(txtName.Text) returns number of characters. SelectionLength = Len(txtName.Text) will cause all characters in text box to be selected


Highlighting the Text

Text in txtName is highlighted when user tabs in. User can type new name without using the Delete key to get rid of old text. Makes application more friendly


Arranging Many Controls

Group box– Used to group related data fields– Controls inside box treated as one logical unit

If you delete the group box, all controls deleted

Tab controlTab control– Organizes a window into logical tabbed pages

Both considered “containers”– They have the capability to hold other controls


Data with Limited Number of Choices

Radio button– Only one button in a group can be selected

Good for mutually exclusive options, i.e. Male or Female– To allow multiple radio buttons to be selected on a window,

use multiple containers Check box

– User can select as many items as he/she wants Good for independent, rather than mutually exclusive options

Both have Text and Checked properties– Text property is the text next to the control– Checked can be True or False


Longer List of Known Items

List box– Contains a list of items a user can select from– User can not enter items not in the list– User may have option to select multiple items

Good alternative to check boxes Combo box

– Contains a list of items a user can select from– User may enter items not in the list– User can only select one item

Good alternative to radio buttons


Common Methods and Properties

SelectedItem property– Indicates the item selected (the text)

SelectedIndex property– Indicates the position of the item clicked

The first item has a SelectedIndex value of 0 Items.Add method

– Adds items to list box or combo box Items.Count property

– Gives the number of items in the list or combo box


Selecting Items from the List Box

SelectionMode property determines how items are selected– When set to One, only one item can be selected– When set to MultiSimple or MultiExtended, user

can select multiple items GetSelected method used to determine

whether or not an item is selected– Syntax: Listbox.GetSelected(Index)


Selecting Items from the Combo Box

Combo box has a text box area and list box DropDownStyle property determines whether

or not user can enter data not in list– DropDown style (default)

Fixed height; user can select from list or enter text– Simple style

Adjustable height; user can select from list or enter text– DropDownList style

user can only select an item from the list


Graphics in the Visual Interface

The Picture box– Has an Image property– Has a SizeMode property

Normal: size of picture box drawn on form sets boundary for the picture

StretchImage: size of image adjusted to fit the picture box AutoSize: size of picture box adjusted to fit image CenterImage: image appears in center of picture box

Use only company logos or art that is professionally designed for this application


Setting the Image Property

Setting at design time– Set the Image property in the Properties box

Setting at runtime– Use the Image.FromFile method to load the

picture If you use this image, you run the risk that someone has

moved or deleted the file Write a routine to allow the user to select the picture in

the event it has been moved or deleted


Naming Conventions: Prefixes


Setting Tab Order

Tab order: the order in which a VB control receives focus when user presses Tab key– Determined by control’s TabIndex property

Tab order is an important component of a user-friendly interface– user should not jump all over the form when

he/she tabs Form must have focus to set tab order


The Tab Order


Common Events

Form Load event– occurs when form is loaded into memory

before form is displayed– all controls are set to initial states

Click event– occurs when a user clicks a control

normally associated with a button SelectedIndexChanged event

– occurs when the user selects an item in the list box or combo box


Common Events

KeyPress event– occurs when the user presses a key

often used for data validation Enter event

– occurs when a control receives focus performs some “preparatory” activities

Leave event– occurs when user leaves a control

perform some finishing touches, such as field validation


An Application ExampleThe Environ-Pure Project

Analyze and define requirements– An easy to use interface to take orders from distributors

Define the controls needed for the visual interface– Determine the data fields to be entered– Determine the appropriate type of control for each data field

Set the Tab Order– Window has a vertical layout, so tab order should flow from

top to bottom


An Application ExampleThe Environ-Pure Project

Code the Event Procedures– Several types of procedures needed

Form Load procedure sets default values Validation procedures needed for several controls Radio buttons should be enabled only if this is a rush order Need procedures to save the data and to exit the application

Test the Project– Create a test plan to test every control– Try to make the application break!


The Visual Interface


Summary

Different controls have different uses– text boxes for open-ended data– masked edit boxes for data with defined pattern– radio buttons for data with limited number of mutually

exclusive choices– check boxes for data with limited number of independent

choices– list boxes for relatively large list with independent choices– combo boxes for relatively large list with mutually exclusive

choices


Summary

Containers are used to hold other items– group boxes used to group related data fields– tab controls used to group data into tabbed pages

Change tab order of controls to make interface more user-friendly– form must have focus to change tab order


Summary

Different events can have different uses– Form Load event initializes values of variables and controls– Click event responds to user clicks on buttons, etc– SelectedIndexChanged event occurs when the user clicks

on list boxes and combo boxes– KeyPress event previews keystrokes before displaying in

control– Enter event performs preparatory tasks, such as

highlighting text– Leave event performs finishing touches

Documents

Copyright (c) 2003 by Prentice Hall Provided By: Qasim Al- ajmi Chapter 3 Some Visual Basic Controls and Events Visual Basic. NET