Multiple Forms and Standard Modules Chapter 7

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

Default File Name and Name Chapter 7 - Part 1

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

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

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

Startup Object (p. 405) Right-click Project name (in Solution Explorer window) and choose Properties. …or… Choose Project | Properties. Chapter 7 - Part 1

Startup Object Click Startup object drop-down arrow and choose form name to be first object (form) that appears. Chapter 7 - Part 1

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

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

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

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

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

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

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

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

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

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

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

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

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 Chapter 7 - Part 1

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. Chapter 7 - Part 1

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

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

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

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

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 Chapter 7 - Part 1

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

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