Multiple Forms, Standard Modules, And Menus Chapter 7 Multiple Forms, Standard Modules, And Menus

Chapter 7 Introduction

Chapter 7 Topics How to add multiple forms to a project How to create a standard module Holds procedures and functions not associated with a specific form Creating a menu system Context menus With commands and submenus that the user may select from

Section 7.1 Multiple Forms Visual Basic Projects May Have Multiple Forms A Form Designated as the Startup Object Is Displayed When the Project Executes Other Forms in a Project Are Displayed by Programming Statements

Form Names Each form has its specific name Programs refer to a form by this name VB assigns a default name Form1 to forms A form’s Name property allows us to set or change the form name Standard prefix for form names is frm Each form also has a file name (.vb extension) Forms are stored on disk using this name To change the file name: Right click in Solution Explorer, select Rename

Adding a New Form to a Project Click Add New Item on the toolbar Or Project on menu, then Add Windows Form Add New Item dialog box appears Click on Windows Form under Templates Change the default name if you wish Click the Open button New form now appears in: Design window Solution Explorer

Switching from Forms to Form Code Design window has two tabs for each form One for form design One for the code associated with a form For two forms named frmMain and frmError, can select from the following tabs: frmMain.vb[Design] Main form design frmMain.vb Main form code frmError.vb[Design] Error form design frmError.vb Error form code

Changing the Startup Form First form created in a project becomes the startup object The form displayed when application runs To make another form the startup object Right-click project name in Solution Explorer Click Properties Click down arrow in Startup Form box Select new startup form from drop-down list Click Ok

Classes and Instances The form design is a class It’s only a design or description of a form Think of it like a blueprint A blueprint is a detailed description of a house A blueprint is not a house The form design can be used to create one or more instances of the form Like building a house from the blueprint In order to use a form in a program, we must first create an instance of it from the design

Creating an Instance of a Form Dim statement used to create instance of form To create an instance of frmError: frmError is the form design name (the class) New frmError creates an instance of the form Variable errorForm refers to the form instance and is used to perform operations on the form The form is not yet visible, but it now exists Show or ShowDialog makes the form visible Dim ObjectVariable As New ClassName() Dim errorForm As New frmError()

Modal Forms & ShowDialog Method A modal form prevents the user from changing focus to another form in the application as long as it remains open For example: Variable errorForm represents an instance of frmError as shown in the previous slide The ShowDialog method displays the form instance named errorForm as a modal form Must close errorForm in order to change focus to another form in the application errorForm.ShowDialog()

Modeless Forms & Show Method A modeless form allows the user to change focus at will to another form in the application while that form remains open For example: Variable errorForm represents an instance of frmError as shown previously The Show method displays the form instance named errorForm as a modeless form Can change focus to other forms in the application while errorForm remains open errorForm.Show()

Closing a Form A form may close itself using the Close method and referring to itself as "Me": As in Me.Close() Private Sub btnClose_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) _ Handles btnClose.Click Me.Close() End Sub

Hiding a Form Closing a Form eliminates it from memory To retain the form in memory but remove it from the display, use the Hide Method: To redisplay the form use the ShowDialog or Show method Me.Hide()

More on Modal and Modeless Forms Display of a modal form causes execution of calling statements to halt until form is closed Display of a modeless form allows execution to continue Tutorial 7-1 demonstrates these differences statement; messageForm.ShowDialog() ' Statements below will ' not execute until the ' Form is closed statement; messageForm.Show() ' Statements below will ' execute right after the ' Form is displayed

The Form Load Event The Load event is triggered just before the form is initially displayed Any code needed to prepare the form prior to display should be in the Load event If some controls should not be visible initially, set their Visible property in the Load event Double click on a blank area of the form to set up a Load event as shown below Private Sub frmMain_Load(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles MyBase.Load End Sub

The Form Activated Event The Activated event is triggered when focus switches to the form from another form or application The Load event is triggered once when the form is initially displayed The Activated event is also triggered when the form is initially displayed Occurs immediately after the Load event The Activated event may be triggered many more times while a form is being displayed

The Form Closing Event The Closing event is triggered as the form is being closed, but before it has closed The Closing event can be used to ask the user if they really want the form closed Private Sub frmMain_Closing(ByVal sender As Object, _ ByVal e As System.ComponentModel.CancelEventArgs) _ Handles MyBase.Closing If MessageBox.Show(“Are you Sure?”, “Confirm”, _ MessageBoxButtons.YesNo) = DialogResult.Yes Then e.Cancel = False ‘continue, close form Else e.Cancel = True ‘cancel form close End If End Sub

The Form Closed Event Closed event triggered after a form is closed Note that it is now too late to prevent the form from being closed (it is already)

Using Objects on a Different Form When code in a form refers to an object, it is assumed that object is in that same form You can refer to an object in another form Simply preface the object name with the variable name associated with that form frmGreeting has a control named lblMessage Set Text property to Hello before displaying Dim greetingForm As New frmGreeting() greetingForm.lblMessage.Text = "Hello!" greetingForm.ShowDialog()

Class-level Variables in a Form Class-level variables are Private by default This means they are not accessible by code in other forms If you want to access from other forms, they must be declared with the Public qualifier: Public sngTotal As Single ' Instead of the declaration ' Dim sngTotal As Single

Public/Private Procedures in a Form Procedures, by default, are Public They can be accessed by code outside of their Form To make a procedure invisible outside its own form, declare it to be Private Tutorial 7-2 provides an opportunity to work with a multiple form application

Section 7.2 Standard Modules A Standard Module Contains Code - Declarations and Procedures - That Are Used by Other Files in a Project

Standard Modules A separate .vb file not associated with a form Contains no Event Procedures Used for code to be shared by multiple forms Procedures or variables used by one form should be declared in that form Procedures or variables used by many forms should be declared in a standard module

Standard Module Syntax Module ModuleName [Module Contents] End Module ModuleName is normally same as .vb file Module Contents are sub procedures and functions which can be Private - only used by functions in that module Public - can be called from outside of the module If not specified, a procedure is public

Adding a Standard Module Click Add New Item on the toolbar Or Project on menu, then Add Module Add New Item dialog box appears Click on Module under Templates Change the default name if you choose Click the Open button A new empty module now appears in: Code window Solution Explorer

Module Level Variables These are declared within a module But outside of any functions or sub procedures in that module If declared Dim or Private, the scope is the module (called module scope) If declared Public, the scope is the entire application (called global scope) Tutorial 7-3 demonstrates the use of a standard module in an application

Application with No Startup Form Must change the startup form to Sub Main Main must be a public sub procedure It must be in a standard module When the application starts No Form will be displayed Main will be given control

You Use the Menu Designer to Create a Menu System Section 7.3 Menus Visual Basic Allows You to Create a System of Drop-down Menus for Any Form in Your Application You Use the Menu Designer to Create a Menu System

Components of a Menu System Menu Name Menu Command Submenu Each drop-down menu has a menu name Each drop-down menu has a list of actions or commands that can be performed Some commands may lead to a submenu

Components of a Menu System Shortcut Key (F7) Access Key (L) Commands can be performed by A key or key combination called a shortcut key A single letter and the Alt key called an access key Menu must be open to use an access key Shortcut key works when menu is not displayed

Components of a Menu System Checked Menu Command Separator Bar A disabled menu command can’t be selected at present and shows as a light color (grayed out) A checked menu command toggles between the checked (if on) and unchecked (if off) states A separator bar helps group similar commands

MainMenu Control Add to form with double-click on MainMenu control in Toolbox Menus & Toolbars section The MainMenu control is displayed in the component tray (bottom of Design window) May have many MenuItem objects with the following key properties: MenuItem name used by VB to identify it MenuItem text displayed to the user Actions in the form of a MenuItem click event Submenu Separator bar

MenuItem Object Names Should begin with mnu Then by convention are spelled, specifying their hierarchical position: mnuFile mnuFileSave mnuFilePrint

MenuItem Text Properties The text property holds the item description displayed to the user If an access key is assigned, that letter must be preceded with an ampersand Object Name Text Property Access Key mnuFile &File F mnuFileSave &Save S mnuFileExit E&xit X

Menu Designer The Menu Designer allows menu creation by filling in a box with the menu text: Enter the next menu name Enter first command in the File menu

Shortcut Keys Keyboard based shortcuts that execute menu commands without using the menu system For example, ctrl-c to Copy to the clipboard These are set via the Shortcut property of each menu item A shortcut is displayed to the user only if the ShowShortcut property is set to true

Disabled MenuItem Objects A menu item is grayed out (disabled) with the Enabled property Paste option is initially disabled and only enabled after something is cut or copied Code initially disables the Paste option Following a cut or copy, Paste is enabled mnuEditPaste.Enabled = False mnuEditPaste.Enabled = True

Adding Separator Bars Right-click menu item, select Insert Separator Separator inserted above the menu item Or create a menu item with one hyphen (-) as the text property

Submenus When selecting a menu item in the designer, a Type Here box appears to its right Begin a submenu by setting up this menu item If a menu item has a submenu, a solid right-pointing arrow will be shown for this item

Inserting, Deleting, & Rearranging To insert a new menu item within the list Right-click the item to follow the new one Choose Insert New from the shortcut menu Use Menu Designer to add new menu items at the end by entering the text to appear To remove a menu item Right-click on the item Choose Delete from the shortcut menu The Menu Designer can rearrange items using a click and drag approach

MenuItem Click Event Procedures Menus and submenus require no code Commands require a click event procedure Double click on the menu item Event procedure created in the code window Programmer supplies the code to execute Double click the MenuItem object named mnuFileExit to create the following Private Sub mnuFileExit_Click(ByVal sender as System.Object, _ ByVal e as System.EventArgs) Handles mnuFileExit.Click Me.Close() End Sub Programmer supplied code Click event procedure created by VB

Standard Menu Items In general follow the conventions that most application menu systems use File is leftmost item with access key Alt-F File item has Exit command, access key Alt-X Help is the rightmost item Help menu has an About command Tutorial 7-4 demonstrates how to create a menu system

Context Menus A pop-up menu that appears on a right-click Context menus are designed for a particular control or set of controls To set up a Context Menu: Double-click ContextMenu control in the ToolBox to add it to the component tray Build menu system using Menu Designer Build Click event procedures as needed Use ContextMenu property of form controls to link desired control(s) to the menu

Section 7.4 The High Adventure Travel Agency Price Quote Application Build an application with multiple forms, a standard module, and a menu system