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Multiple Forms,

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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,


1
Chapter 7
  • Multiple Forms,
  • Standard Modules,
  • And Menus

2
7.1Introduction
3
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

4
7.2Multiple Forms
  • Visual Basic .NET Projects May Have Multiple
    Forms
  • If One of the Forms Is the Startup Object, It Is
    Displayed When the Project Executes
  • The Other Forms Are Displayed by Programming
    Statements

5
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

6
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

7
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

8
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
    built

9
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()
10
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

errorForm.ShowDialog()
11
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

errorForm.Show()
12
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
13
Hiding a Form
  • Closing a Form eliminates it from memory
  • To simply make it not visible, use the Hide
    Method
  • To bring it back use the ShowDialog() or Show()
    Methods

Me.Hide()
14
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
15
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
16
A Form's Activated Event
  • The Activated Event is triggered when the user
    switches to the from from another form or another
    application
  • It is also triggered after the Load Event

17
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

18
A Form's Closed Event
  • The Closed Event is triggered after a form is
    closed
  • Note that it is now too late to prevent the Form
    from being closed (it is already)

19
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
g()
20
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
21
Procedures Have Similar Access Rules
  • Procedures, by default, are Public
  • They can be accessed by code outside of their
    Form
  • To prevent this from happening, declare them to
    be Private

22
7.3Standard Modules
  • A Standard Module Contains Code - Declarations
    and Procedures - That Are Used by Other Files in
    a Project

23
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

24
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

25
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)

26
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

27
7.4Menus
  • Visual Basic .NET 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

28
Components of a Menu System, I
Menu Name
Shortcut Key
Checked Menu Command
Menu Command
Separator Bar
Submenu
29
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

30
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

31
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

32
MainMenu Control
  • When used, the MainMenu control appears in the
    component tray (at the bottom of the Design
    Window)
  • It is composed of MenuItem Objects, such as
  • Menu Name
  • Menu Command
  • Separator Bar
  • Sub-Menu Command

33
MenuItem Names
  • Should begin with "mnu"
  • Then by convention are spelled, specifying their
    hierarchical position
  • mnuFile
  • mnuFileSave
  • mnuFilePrint

34
MenuItem Text Properties
  • The text property is the text that appears on the
    menu
  • 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

35
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
36
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

37
Disabled MenuItem Objects
  • The status of a menu item (enabled vs. disabled)
    is controlled by the Enabled property True is
    Enabled

mnuEditPaste.Enabled True
38
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)

39
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
    Designer
  • To Delete a menu item, right-click/Delete
  • To Rearrange menu items, click and drag them in
    the Menu Designer

40
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

41
Context Menus
  • To establish a pop-up menu when a control is
    right-clicked
  • 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
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