CIS 230, Visual Basic

Ch. 6 Notes, page 1

Objective #1: Create a project with multiple forms.

• Practically-speaking, you must use multiple forms  in a VB project to create an application that is non-trivial. While you could make extensive use of frames to group related objects and be very creative with the Visible property, limiting yourself to one form would make coding unnecessarily complicated. Creating a pleasing user interface requires multiple forms in a project.
• You can create a new form (more formally known as a form module) simply by choosing the menu command Project/Add Form and then selecting Form from the resulting window.
• You can add a preexisting form to a project by choosing the menu command Project/Add Form and then selecting the Existing tab. This does not duplicate the added form which may exist as part of another VB project. It simply links that form (.frm file) to your current project. If the form is relocated in the future, the project will not be able to access the form.
• You can add as many forms as you wish to a project but adding too many may make the project unmanageable.
• The first form that is displayed or activated in a project is called the startup form.

Objective #2: Use the Show and Hide methods to display and hide forms.

• The Hide method of a form makes it disappear. For example, if the form frmLevel2 were placed directly behind form frmLevel1, then the statement    frmLevel1.Hide      would cause frmLevel1 to disappear and reveal frmLevel2.
• The Show method of a form makes it appear on the screen.
  • The Show method can be set to 0 for modeless or 1 for modal. (The VB constants VBModeless and VBModal also can be used as constant values.) For example, the statement
       frmLevel1 Show 1    displays frmLevel1 in a modal state. The default is modeless if the statement         frmLevel1 Show      is used without specifying a value.
  • Displaying a form in modeless state allows the user to close that form or simply ignore by making another form active.
  • Displaying a form as modal, you require the user to respond to the form in some way. This can be more effective than using a message box, especially since you can do much more with a form than a simple message box.
• Two special events occur behind the scenes every time that a form first displays in a project, the Form Load and Form Activate events, which are not user generated.
  • The Form_Load calls the form module into memory (RAM).
  • A split second later the Form_Activate event occurs and actually activates the form, passing control to it. If the form is hid with the Hide method, only the Form_Activate method will be invoked when it is shown again. If there are tasks or initializing steps that must be performed every time the form is shown, you should place those tasks and statements in the form's Form_Activate procedure.
• If you no longer need to use a form throughout the remainder of the executing project, you should conserve memory by unloading the form. This can be done with the statement        Unload frmLevel1    . Simply hiding a form does not clear the memory that it uses which could be significant on older computers in projects that use many forms.
• While the Show method automatically loads a form, you can intentionally load a form before you plan to use it in order to save time and make the form appear faster. This can be done with the statement       Load frmLevel1
• The Me keyword can be used anywhere in your code that you would use the form name of the currently active form. If the form frmLevel1 was the active form then the statement        Unload Me    would clear the form from the memory.

Objective #3: Create procedures that are accessible from multiple form modules.

• When you create a new general procedure you must carefully determine whether it would be something that is useful to a number of form modules or only one form module. If is is only appropriate for one form module then you should place it in that form module and use the keyword Private in its header. If you think that the procedure could be used in numerous forms then you should place it in a standard code module and use the keyword Public in its header.
• A standard code module (.bas file) is not associated with a particular form but is present within the project. In fact, you should (but are not required to) name the code module with the same name as the project itself (the extension will be .bas instead of .vbp though).
• To add a code module, choose the menu command Project/Add Module and then select Module on the New tab. Of course you can reuse standard code modules that belong to other projects as well.
• Once you have created a code module, it will appear in the Project Explorer window.
• By placing general procedures within a code module you can easily make them accessible to multiple form modules. Any procedure in a standard code module can be called by any procedure in any module of the project. However, if you use the Public keyword in the header of a procedure in a form module, then that procedure can also be called by procedures in other modules.

Objective #4: Differentiate between variables that are global to a project and those visible only to a form.

• Variables and constants can have three different levels of scope: local, module level, and global. It is wise to keep the scope of a variable as narrow as possible. That is, you should try to refrain from using module level and global variables. You may have difficult to debug side effects in your logic if you use globals.
• If you do wish a variable to be accessible to more than one form module, you must make it a global. Simply use the keyword Public instead of Dim in its declaration statement. However, it may confuse those who read your program if you "hide" global variables in form modules in this way. You should always declare such global variables in the general declarations section of the project's standard code module so that they are easy to find and identify. You still have to use the keyword Public to make the variable global even if it is declared in the general declarations section of the code module.
• You should use the the single letter prefixes of g and m within identifiers (i.e. names) of global and module level variables respectively. Therefore, the variable name for a global might be gcurSalary. Local variables do not need a prefix since it is assumed that most of your variables will have local scope.
• Besides the aspect of a variable's scope, it is important to manage a variable's lifetime as well. Local variables are only stored in memory while a procedure is executing. As soon as the procedure ends, its local variables reset to zero (or are actually abandoned by the computer's memory.) If you wish to keep track of a running total for example, throughout the execution of a form, you should declare the variable as Static. Simply use the keyword Static instead of Dim. For example,         Static intRunningTotal As Integer    declares intRunningTotal in such a way.
• Read the Guidelines for Declaring Variables and Constants section on p. 216 very closely. You will be responsible for following those rules and conventions.

Objective #5: Create an About box using a form.

• Most Windows applications give the user the opportunity to see the name and version of the software in an About box. Often "About..." is a menu command under the Help menu. You can easily place such information on a form with labels and add a menu option or command button that invites the user to see this info.
• VB also offers a template About Dialog form that can be found by choosing the menu command Project/Add Form.

Objective #6: Add a splash screen to your project.

• A splash screen can be added to a VB project to make it look professional as well. A splash screen loads as soon as a user executes a program. It often makes it appear as if the application is loading faster than it really is.
• You can create your own splash screen or you can add a VB template found under the Project/Add Form menu command. If you add your own, you should make sure that program execution begins with the special sub procedure Main that is located in your .bas standard code module.

Objective #7: Set the startup form or Sub Main to start project execution.

• You can choose to have one of the forms in a VB project chosen as the startup form. The startup form is simply the first form to load and execute. You can select any form in your project as the startup form from the Project/Project Properties... menu command. Under the general tab you can select the "startup object."
• You can also choose the Main sub procedure to be the startup object of a project. In this case, any code within the Main sub procedure will execute immediately. In this case if you wish to show a splash screen, you must show the splash screen form with a command like    frmSplash.Show         since that will activate the splash screen.

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