Multiple Forms and Standard Modules Chapter 7. Chapter 7 - Part 12 Form Names and File Names Default Name Property: Form1 Default File Name: Form1.vb

Multiple Forms and Standard Modules

Chapter 7

Chapter 7 - Part 1 2

Form Names and File Names

Default Name Property: Form1 Default File Name: Form1.vb

Code stored in the .vb file Should assign descriptive form names for

multiple-form programs Need to do more than change the

Name property: Also change file name Also change Startup Object


Default File Name and Name


Changed File Name and Name

Must keep .vb filename extension.


Adding a Form

If program crashes because it can’t find a form, you might need to add it again:

1. Choose Project | Add Existing Item or click and click Add Existing Item orpress Shift + Alt + A.

2. Choose .vb filename.

3. Click Open.


Removing a Form

Right-click form in the Solution Explorer window Choose Delete from the shortcut menu to

remove the form from the project and delete the .vb file.

Choose Exclude From Project to remove the .vb file from the project but not delete it.


Startup Object (p. 405)

Right-click Project name (in Solution Explorer window) and choose Properties.…or…

Choose Project | Properties.


Startup Object

Click Startup object drop-down arrow and choose form name to be first object (form) that appears.


Add Form

Click Add New Item on toolbar.

Keep the .vb extension


Switching Between Forms

Active FormCode windowfor frmStates form

frmstates form


Form File Contents

Coding Class declaration

Program structure describing object’s properties and methods.

All objects (such as form, list box, etc.) have properties (such as Name) and methods (such as AddItem).

•Name stored in form’s Name property

•Code between Public Class and End Class belong to class declaration for form.


The Class Declaration…

Does not create the form. Describes the form. Acts like a house blueprint.

Describes the form (house). Used to build an instance of the form (house).

(see illustrations on p. 406). Creates 1+ instances of the form; use

instances to display form onscreen. Create class at Design time.

Instantiate class at Run time.


Instance of Form

1st step to display form: create an instance.Dim ObjectVariable As New ClassName()

ObjectVariable Name that refers to instance of form, sort of

like an alias (not name of form itself though) Holds memory address of object (form) so that

you can use it ClassName()

Form’s class name—the name used in the Name property for a form


Example

Dim errorForm As New frmError() errorForm is object variable name that

creates instance of actual form frmError is the class (name) of the actual

form As New causes instance of the form to be

created in memory Memory address assigned to object variable

name errorForm

Does not actually display form


ShowDialog Method

Modal method (most common) No other form can receive focus until the

modal form is closed. Forces user (or timer) to acknowledge active

form ObjectVariable.ShowDialog() errorForm.ShowDialog()


Show Method

Modeless form Allows user to switch focus to another form

while the modeless form is displayed ObjectVariable.Show() errorForm.Show()


Close Method

Closes a form and releases it from memory. Me.Close()

Me—current instance of the form; refers to itself

Close—closes current instance Use to close a form in a multiple-form

program without terminating the application


Hide Method

Removes form from the screen. Keeps form in memory; does not release it. Acts like changing form’s Visible property to

False.


Other Events

Load Triggered immediately before a form displays. Example: populate a list box

Activated Triggered when user switches to a form from

another form. Triggered when for is initially displayed—after

the Load event. Base Class Events (class name drop-down) Activated (method drop-down)


Closing Events

Triggered as form is being closed but before it finishes closing.

Useful to ask user if really wants to close form Event procedure parameter list includes

ByVal e As System.ComponentModel e has Boolean property named Cancel

True—prevents form from closing False—continues closing form


Closing, Continued

Yes and No buttons DialogResult.Yes

Set e.Cancel property to False to close form Otherwise (i.e., DialogResult.No)

Set e.Cancel property to True; prevent closing


Closed Event

Trigged after a form closes. Does not prevent a form from closing; only

responds once the form is closed. Refer to p. 415 for more information.


Accessing Objects on Different Forms

Default Controls are on same form as the statement

that accesses it. lblOutput.Text = FormatCurrency(decTotal)

Allowance Write code to access objects on different

forms Dim resultsForm As New frmResults()

resultsForm.lblOutput.Text = decTotal


Class-Level Variables

Accessible to all statements on that form. Not accessible, by default, to statements on

other forms. Class-level variables are private by default

Accessible outside the file containing the class, use the Public key word: Public decTotal As Decimal


Procedures

Private Executable only from same form

Public (default setting) Also executable by statements outside of the

form


Standard Modules

File (.vb) containing code Variable declarations Procedures Functions

Not associated with a particular form Useful to organize code in multi-form projects Assign descriptive names (p. 423) Add a standard module (p. 424)


Private and Public Procedures

Private Accessible by statements only inside that

module Public

Also accessible by statements outside that module

Default if access specifier not provided


Module-Level Variables

Module variable not declared within a procedure or function.

Accessible by an sub procedure or function in the module.

Not accessible to statements outside the module if declared with Dim or Private (module scope).

Accessible to statements outside module if declared with Public (global scope). Use g_ prefix for global variables. See warning on p. 426.


Tutorials

Tutorial 7-1 Modal and Modeless

Tutorial 7-2 Multiple Forms

Tutorial 7-3 Standard Module

Documents

Multiple Forms and Standard Modules Chapter 7. Chapter 7 - Part 12 Form Names and File Names Default Name Property: Form1 Default File Name: Form1.vb