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Multiple Forms,


How to add multiple forms to a project. How to create a ... Plus if there is a access key, it is preceded with an ampersand, e.g. Object Name Text Property ... – PowerPoint PPT presentation

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Title: Multiple Forms,

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

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

7.2Multiple Forms
  • Visual Basic .NET Projects May Have Multiple
  • If One of the Forms Is the Startup Object, It Is
    Displayed When the Project Executes
  • The Other Forms Are Displayed by Programming

Form Names
  • Each Form has its specific name
  • This name is set/changed with the Name Property
  • Each form also has a file name (.vb)
  • To change the file name
  • Right click its entry in the Solution Explorer
  • Choose Rename

Adding a New Form
  • Add New Item on the tool bar
  • The Add New Item dialog box appears
  • Click on Windows Form under Templates
  • Change the default name if you wish
  • Click Open

Switching between Design and Code
  • The Design window has the following tabs
  • frmMain.vbDesign Form Design Itself
  • frmError.vbDesign Error Form Design
  • frmMain.vb Main Code
  • frmError.vb Error Code

Classes and Instances
  • When you create a Form at design time, you are
    just creating a general description of a Form(It
    does not actually exist at that moment)
  • Analogy It is a blueprint of a Form
  • An Instance must be created to actually have a
    Form at run time
  • Analogy What the blueprint describes is actually

Creating an Instance of a Form
  • It must be declared, syntax
  • For example
  • It is still not visible, but a form object has
    been instantiated
  • Refer to it using the variable errorForm

Dim ObjectVariable As New ClassName()
Dim errorForm As New frmError()
Modal Form/ShowDialog Method
  • When a Modal Form is displayed, no other form in
    the application can receive the focus until the
    modal form is closed
  • Use the ShowDialog Method to display a modal form

Modeless Form/Show Method
  • A Modeless Form allows the user to switch focus
    to another form in the same application
  • Use the Show Method to display a modeless form

Closing a Form
  • A form may close itself using the Close Method
    and referring to itself as "Me"
  • As in

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 simply make it not visible, use the Hide
  • To bring it back use the ShowDialog() or Show()

More About Modal and Modeless
statement messageForm.ShowDialog() ' Statements
below will ' not execute until the ' Form is
closed statement
statement messageForm.Show() ' Statements below
will ' execute right after the ' Form is
displayed statement
A Form's Load Event
  • The Load Event is triggered just before the form
    is initially displayed
  • If code needs to execute at this time, it must be
    contained in that event handling procedure

Private Sub frmMain_Load(ByVal sender As
System.Object, _ ByVal e As System.EventArgs)
Handles MyBase.Load End Sub
A Form's Activated Event
  • The Activated Event is triggered when the user
    switches to the from from another form or another
  • It is also triggered after the Load Event

A Form's Closing Event
  • This Event is triggered as the form is in the
    process of closing, but before it has closed
  • For instance, one might want to ask the user if
    they really want the form closed

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

Accessing Objects on a Different Form
  • When code in a form refers to an object, it is
    assumed that that object is in the same form
  • To refer to an object in another form, preface
    the object name with the variable name associated
    with that form

Dim greetingForm As New frmGreeting() greetingForm
.lblMessage.Text "Hello!" greetingForm.ShowDialo
Class-level Variables and Multiple Forms
  • Class-level variables are Private by default
  • This means they are not accessible by code in
    other forms
  • If you wish them to be, they must be declared
    with the Public qualifier

Public total As Single ' Instead of the
declaration ' Dim total As Single
Procedures Have Similar Access Rules
  • Procedures, by default, are Public
  • They can be accessed by code outside of their
  • To prevent this from happening, declare them to
    be Private

7.3Standard Modules
  • A Standard Module Contains Code - Declarations
    and Procedures - That Are Used by Other Files in
    a Project

Furthermore, Standard Modules
  • Are not associated with a Form
  • Contain no Event Procedures
  • Are saved in files with a .vb extension
  • Are used to hold code that is used by multiple
    Forms, or for command-line programs

Standard Module Syntax
Module ModuleName Module Contents End Module
  • A Module will contain Sub procedures and
    Functions, they can be
  • Private - only used by functions in that Module
  • Public - can be called from outside of the Module

Module Level Variables
  • These are declared within a Module
  • But not within Functions or Sub procedures in
    that Module
  • If declared Dim or Private, their scope is the
    Module (called module scope)
  • If declared Public, their scope is the
    application (called global scope)

Application with No Startup Form
  • Designate a Public Sub procedure named "Main" as
    the startup object
  • It must be in a Standard Module
  • When the application starts
  • No Form will be displayed
  • "Main" will be given control

  • Visual Basic .NET Allows You to Create a System
    of Drop-down Menus for Any Form in Your
  • You Use the Menu Designer to Create a Menu

Components of a Menu System, I
Menu Name
Shortcut Key
Checked Menu Command
Menu Command
Separator Bar
Components of a Menu System, II
  • Menu Names - each drop-down menu has a name
  • Menu Command - the list of actions in the
    drop-down list
  • Shortcut Key - a key or combinations of keys to
    activate the command from the keyboard

Components of a Menu System, III
  • Disabled Menu Command - a command that is not
    applicable is grayed out (and is not selectable)
  • Checked Menu Command - some commands are toggles
    - checked when on, unchecked when off

Components of a Menu System, IV
  • Submenu - a command may lead to another menu
  • Separator Bar - a horizontal bar used to separate
    groups of commands

MainMenu Control
  • When used, the MainMenu control appears in the
    component tray (at the bottom of the Design
  • It is composed of MenuItem Objects, such as
  • Menu Name
  • Menu Command
  • Separator Bar
  • Sub-Menu Command

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

MenuItem Text Properties
  • The text property is the text that appears on the
  • Plus if there is a access key, it is preceded
    with an ampersand, e.g. Object Name Text
    Property mnuFile File mnuFileSave Save mnuFil
    eExit Exit

Menu Designer
  • The Menu Designer speeds creation of menus with a
    fill in the box with text scheme

Enter the next menu name
Enter first command in the File menu
Shortcut Keys
  • These are the key shortcuts that get one directly
    to the command action without going through the
    menu system(e.g., CTRL-C for Edit/Copy)
  • These are set via the Shortcut Property of each
    menu item

Disabled MenuItem Objects
  • The status of a menu item (enabled vs. disabled)
    is controlled by the Enabled property True is

mnuEditPaste.Enabled True
Adding Separator Bars
  • Either make the menu items Text property equal
    to "-" (hyphen)
  • Or right-click an existing menu item and select
    Insert Separator (it will be inserted above the
    menu item)

Inserting, Deleting, RearrangingMenu Items
  • To Insert a new menu item above an existing one,
    right-click to use the context sensitive menu
  • To Insert a new item at the end, use the Menu
  • To Delete a menu item, right-click/Delete
  • To Rearrange menu items, click and drag them in
    the Menu Designer

Standard Menu Items
  • In general follow the conventions that the
    majority of application menu systems use
  • Specifically
  • 'File' is the leftmost menu item
  • The File menu has an 'Exit' command
  • 'Help' is the rightmost menu item
  • The Help menu has an 'About' command

Context Menus
  • To establish a pop-up menu when a control is
  • Add the ContextMenu control to the component tray
  • Build the menu system with the Menu Designer
  • Add a Click Event procedure
  • Then associate the menu with the control by
    setting the control's ContextMenu property to the
    established menu