1. Multiple Forms and Standard Modules
Chapter 7

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
Chapter 7 - Part 1

3. Default File Name and Name
Chapter 7 - Part 1

4. Changed File Name and Name
Must keep .vb filename extension.
Chapter 7 - Part 1

5. Adding a Form
If program crashes because it can’t find a form, you might need to add it again:
Choose Project | Add Existing Item or click and click Add Existing Item or press Shift + Alt + A.
Choose .vb filename.
Click Open.
Chapter 7 - Part 1

6. 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.
Chapter 7 - Part 1

7. Startup Object (p. 405)
Right-click Project name (in Solution Explorer window) and choose Properties. …or…
Choose Project | Properties.
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8. Startup Object
Click Startup object drop-down arrow and choose form name to be first object (form) that appears.
Chapter 7 - Part 1

9. Add Form Click Add New Item on toolbar. Keep the .vb extension
Chapter 7 - Part 1

10. Switching Between Forms
Active Form
Code window
for frmStates form
frmstates form
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11. 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.
Chapter 7 - Part 1

12. 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.
Chapter 7 - Part 1

13. 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
Chapter 7 - Part 1

14. Example Dim errorForm As New frmError() Does not actually display form
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
Chapter 7 - Part 1

15. 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()
Chapter 7 - Part 1

16. Show Method Modeless form ObjectVariable.Show() errorForm.Show()
Allows user to switch focus to another form while the modeless form is displayed
ObjectVariable.Show()
errorForm.Show()
Chapter 7 - Part 1

17. 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
Chapter 7 - Part 1

18. Hide Method Removes form from the screen.
Keeps form in memory; does not release it.
Acts like changing form’s Visible property to False.
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19. Other Events Load Activated
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)
Chapter 7 - Part 1

20. 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
Chapter 7 - Part 1

21. 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
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22. 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.
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23. 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
Chapter 7 - Part 1

24. 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
Chapter 7 - Part 1

25. Procedures Private Public (default setting)
Executable only from same form
Public (default setting)
Also executable by statements outside of the form
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26. 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)
Chapter 7 - Part 1

27. Private and Public Procedures
Accessible by statements only inside that module
Public
Also accessible by statements outside that module
Default if access specifier not provided
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28. 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.
Chapter 7 - Part 1

29. Tutorials Tutorial 7-1 Tutorial 7-2 Tutorial 7-3 Modal and Modeless
Multiple Forms
Tutorial 7-3
Standard Module
Chapter 7 - Part 1