lecture 3 - displaying dialog boxes (vb 2008)

8/14/2019 Lecture 3 - Displaying Dialog Boxes (VB 2008)

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Lecture 3: Displaying Dialog Boxes


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Introduction VB .NET provides a number of built-in Dialog Boxes

Each of which provides Dialog-based advanced functionality: Displaying Messages to Users; Allowing users to Choose Fonts and Color; Allowing users to Open and Save files; Allowing users to Print from your Application.

These help you to provide a professional GUI for your Applications

Very quickly and quite impressively (RAD Development). This, and next lecture, we will discuss 4 standard Dialog Boxes:

The MessageBox (weve seen this!) But now, we examine it in more detail (more buttons; icons, etc)

The FontDialog Control

Which supports the easy, UI-based changing of Font and text-properties. The SaveFileDialog Control

Which supports the easy, Dialog-based saving of files.

The OpenFileDialog Control That allows users to conveniently open files.


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Dialog Boxes 1: The MessageBox

The Dialog Box used most often is the MessageBox As we know, MessageBoxes support:

Display information to users Warnings, Error Messages, Informative Messages, etc

Collect information, regarding a simple choice (A Button Click).

We have already used simple MessageBoxes, quite a bit

To display messages via MessageBox.Show().

As we will see, Show() takes various parameters, to display: A Message (1st parameter)

A Caption/Title (2nd parameter)

A Set of Buttons (3rd

parameter) A Display Icon (4th parameter)

Which Button is Default (5th parameter).

First, lets look at icons


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Selecting a Display Icon

One of severalDisplay Iconscan be selected for display Using the MessageBoxIcon Enumeration (a set ofSystem Constants)

An Error Icon Use the System Constant, MessageBoxIcon.Error Also called the Stop Icon:

MessageBoxIcon.Stop

A Question Icon

Use: MessageBoxIcon.Question A Warning Icon MessageBoxIcon.Warning

Also called the Exclamation Icon: MessageBoxIcon.Exclamation

An Information Icon (MessageBoxIcon.Information) Also called the Asterisk Icon:

MessageBoxIcon.Asterisk

No Icon MessageBoxIcon.None

Which is to be used is specified by using the System Constant in the Show() Method of MessageBox (4th parameter).

We discuss this, shortly


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MessageBox Buttons

Several button combinationscan be displayed Using the MessageBoxButtons Enumeration ()

AbortRetryIgnore i.e., MessageBoxButtons.AbortRetryIgnore in the 3rd parameter of Show() Displays Abort, Retry, and Ignore buttons.

OK Displays an OK button

OKCancel Displays OK and Cancel buttons

RetryCancel Displays OK and Cancel buttons

YesNo Displays Yes and No buttons

YesNoCancel Displays Yes, No, and Cancel buttons

Which is displayed is specified in MessageBox.Show() Note that operation is Modal:

Users must click one, for the main program to continue

Information about which is clicked will be returned to the call point


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Setting the Default Button

A Default button may be selected.

Using the MessageBoxDefaultButton Enumeration. This is the button activated when the user hits

The Default button is specified using the following options: Button1 (the Default value)

The 1st button from the left in the MessageBox is the Default. i.e., MessageBoxDefaultButton.Button1

Button2 The 2nd button in the MessageBox is the Default.

Button3 The 3rd button in the MessageBox is the Default.

If fewer buttons are on the MessageBox than the option indicates The Default button is selected by cycling clockwise. So forMessageBoxButtons.YesNo, the 3rd button is Yes.

This is specified in the 5th parameter of MessageBox.Show()


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The Show Method

A MessageBox is displayed using the Show() Method.

The full Syntax of the Show() method is:

MessageBox.Show( text, caption, Buttons, Icon, DefaultButton )

Any/All parameters may be omitted or used as desiredSo MessageBox.Show( text ) MessageBox.Show( text, caption )are also OK, for instance

Among these parameters: Text is a String orString Variable.

Used to display text in the main area.

Caption is also a String orString Variable. Used to display text in the title bar.

Buttons represents the MessageBoxButtons enumeration.

Icon represents the MessageBoxIcons enumeration.

DefaultButton represents the MessageBoxDefaultButton enumeration.


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The DialogResult Enumeration When a MessageBox Button is clicked by a user...

Information about the Event is returned to the point of call.

i.e., the point in the code where Show() was called. What is returned is a defined value of the DialogResult enumeration.

Which indicates which button was actually chosen. Note: what is done with that information is up to the programmer!

DialogResult enumeration members are quite intuitive:

Each type ofButton has a corresponding DialogResult value: Abort Cancel Ignore No None

OK Retry Yes

Each value is represented in the standard enumeration style e.g.: RetryDialogResult.Retry

Such a returned value can be used in a conditional

expression.


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MessageBox Example


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MessageBox Example (Cont.)


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The FontDialog

The FontDialog Class supports UI-based font selection To help users choose which font to use in displaying their data (text).

Available fonts: those installed on the users system.

The FontDialogcan be used as either a:1. VB.NET Class, by

Declaring an Instancein the code;

Setting its propertiesin code.

2. VB .NET Control, by Dragging the Control

from the ToolBox. Setting its properties in code,

or in the Properties Window.

Either way, it will have the same methods, properties, and events And will be displayed, as shown above By invoking the OpenFileDialogs ShowDialog() Method.


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FontDialog Properties and Methods

FontDialog has the following Properties : Name: name of the Control instance ( as usual ).

Color:Indicates the color selected in the Dialog.

Font: Indicates the font selected in the Dialog.

MaxSize / MinSize: Indicates the maximum / minimum selectable font size ( in points ).

ShowApply: Indicates whether the Dialog contains an Apply button.

ShowColor: Indicates whether the Dialog displays the Colorchoice.

ShowEffects: Indicates whether the Dialog contains options for special effects ( underline, text color, etc ).

ShowHelp: Indicates whether the Dialog displays a Help button.

Note that user choices do not take effect automatically We must ask the FontDialog what the user as chosen, and code the effect!

We will use only one Method ofFontDialog: ShowDialog(), which displays the Dialog, as usual.


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FontDialog: Example

Lets open and use the TextEditorfrom our previous lecture


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FontDialog: Example (cont)

To demonstrate proper functionality, here we change:

The text Font to Comic Sans MS Bold12pt

The text Color to light purple.

lecture 3 - displaying dialog boxes (vb 2008)

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