Wyo VB - Ch. 8 Notes

Objective #1: Create a project with multiple forms.

• You can create a new form (also called form module) by choosing the menu command Project/Add Form and then double-clicking Form on the resulting window. You should always rename a form by changing its Name property as soon as you add a form to a project. While it is conventional to name the first form in a VB project frmMain, you can choose any appropriate name for a second form as long as it begins with the prefix frm. I also highly recommend saving the form with the File/Save Form As... menu command as soon as you've added it to the project. This may prevent you from accidentally saving the form outside of the folder that you created for your VB project.
  
  
• You will see that along with your frmMain, any new form that you have added to a project will appear in the Project Explorer window. You can view a form's interface by double-clicking its entry in the Project Explorer window. Each form has a separate code window that can be viewed by first highlighting the form and clicking the View Code button in the Project Explorer window.
  
  
• To remove a form from a project, you can right-click its entry in the Project Explorer window and choose the Remove Form menu command on the shortcut menu. This technique does not delete it from your computer's hard drive if it was already saved.
  
  
• 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 also use the Project/Add File... menu command to add a form to your project.
  
  
• You can add as many forms as you wish to a project but adding too many forms may make the project unmanageable.
  
  
• You can add a splash screen to a VB project by choosing the Splash Form entry from the window that appears when you use the Project/Add Form menu command. This splash form is a template that is provided with VB. This template is automatically named frmSplash.
  
  
• The first form that is displayed or activated in a project is called the Startup Object of the project. Typically, your frmMain will be the Startup Object of the project by default. You can make a splash form the Startup Object by choosing the Project/Project Properties... menu command and selecting it on the Startup Object combo box that appears on the General tab. This will cause your project to first display the splash form. However, you will have to use the Show method to make sure that your frmMain appears after the user closes the splash form.
  
  
• You can create an MDI project with Visual Basic. An MDI (Multiple Document Interface) project is one in which there is one parent form and several child forms. The parent form must be created using the Project/Add MDI Form menu command. A parent form has a gray background. You cannot place controls such as labels, textboxes, and command buttons on a parent form. However, a parent form can (and usually does) have a menu. Then add child forms to the MDI project using the Project/Add Form menu command. However, to make a form a child form, you must set its MDIChild property to True. This causes the child form to appear inside of the parent form. The user can drag and move the child form but only inside of the parent form. This is the interface that you are already familiar with in MS Word where the application itself opens one parent form and new Word documents are child forms. It is still proper to include other forms in the MDI project that are not parent or child forms. For example, it is conventional to use a normal, non-child form for your About and Splash Screen forms.
• A project that does not contain a parent form is called an SDI project (single document interface.)

Objective #2: Properly use the Show and Hide methods as well as the Load and Unload events for forms.

• The Hide method of a form makes it disappear. However, the form is still loaded in the memory (i.e. RAM) of the computer. So it can be quickly displayed later in the program if necessary. 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.
  
  
• If there is no need to use a form later in the program, then you should use the Unload event to unload the form from the computer's memory by calling the Unload event as in:
  
  Unload frmLevel1
  
  
• 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. Instead of the values 0 and 1, you can use the VB constants VBModeless and VBModal.For example, the statements
    
    frmLevel1.Show 1   
    
    or
    
    frmLevel1.Show vbModal
    
    display the form named frmLevel1 in a modal state. Since the default is modeless, the statement        
    
    frmLevel1.Show     
    
    is equivalent to the statements
    
    frmLevel1.Show 0
    
    or
    
    frmLevel1.Show vbModeless
    
    
  • Displaying a form in modeless state allows the user to close that form (with the X in the upper-right corner of the window) or simply ignore it by clicking on an area of another form to make the other form active.
    
    
  • Displaying a form as modal requires 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. In fact, it is better to place code that you wish to use to initialize or set initial properties of various objects in the Form_Activate event procedure rather than the Form_Load event procedure.
    
    
• 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 that form from the memory of the computer.
  
  
• When the user clicks your project's File/Exit menu command or whenever you want your project to end, you should use the following For Each loop to be sure that all of your forms are unloaded. Otherwise, it may appear to the user that your project has been exited but one or more of its forms may still be loaded in the memory (RAM) of the computer. This could cause the person's computer to crash due to lack of memory eventually after he has opened other programs.
  
  Dim frmTemp As Form
  
  For Each frmTemp In Forms
     Unload frmTemp
  Next
  
  End
  
  In the code segment above, frmTemp is a local variable that could have any name. It is being declared as a Form object (rather than an Integer, Single or String variable). The For Each loop is a special kind of For loop that cycles through all of the forms in your projects Forms collection. We won't be studying collections in this course but behind the scenes VB keeps track of all of the forms in a project by storing them in a Forms collection. By the way, there are also collections called CommandButtons, Labels, etc.

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

• A standard code module is not associated with a particular form but is included within the project.
• It is conventional to name your project's standard code module file with the name of the project ( e.g. Ch8Proj1.bas ) or as stdCode.bas. A standard code module uses a .bas file extension instead of .frm which is reserved for VB forms. The Name property of your standard code module should be stdCode.
• To add a standard code module to your project, use the menu command Project/Add Module and then double-click Module on the New tab. Of course you can reuse standard code modules that belong to other projects as well by copying and pasting it into other project folders.
• Once you have created a code module, it will appear in the Project Explorer window. It can be accessed by double-clicking its entry there or by selecting it and clicking the View Code button.
• A standard code module only has a code window. There is no form interface associated with it.
• By placing general procedures and functions within a code module you can easily make them accessible to multiple form modules. Any procedure in a standard code module can be called from any form in your project. However, the Public keyword must be used in the header of the procedure or function. Using the Private keyword would only allow you to call the procedure or function from within the standard code module itself.
• When you create a new general procedure or a function, 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.
• For example, here is a short standard code module that contains one public general procedure and one public function:
  
  Option Explicit

  Public Sub Pause(intSeconds As Integer)
     Dim sngCurrentTime As Single
  
     sngCurrentTime = Timer
  
     Do While (Timer < sngCurrentTime + intSeconds)
  
        If (Timer = 0) Then       ' if midnight
           sngCurrentTime = 0
        End If
  
     Loop
  
  End Sub

  Public Function intGetRandom() As Integer
     intGetRandom = Int(Rnd() * 11) + 0
  End Function
  

Objective #4: Create an About form.

• Most Windows applications give the user the opportunity to see the name and version of the software in an About form. 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 #5: 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 by giving the user something to read while the first form is being loaded behind the scenes.
  
  
• 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 general procedure Main that should be located in your standard code module.

Objective #6: 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."
  
  
• However, you should choose the Main general procedure to be the startup object of a project. In this case, any code within the Main general 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 vbModal      
  
  since that will activate the splash screen.
  
  
• Your Main general procedure should look something like this:
  
  Private Sub Main()
     frmSplash.Show vbModal
     Load frmParent
     Load frmMain
  End Sub
  
  where the splash screen is being displayed with vbModal so that the user must close it before continuing. While he is reading your splash screen, your parent form and perhaps the first child form that needs to be shown within the parent form is being loaded. Within the command button on the splash screen is the actual code that would show the frmMain such ( frmMain.Show).
  

Objective #7: Use timer objects.

• A timer object can be added to a form by double-clicking the timer control in the Toolbox. It looks like a stopwatch.
• A timer object has an Interval property which can be set to any whole number between 0 and 65536. The Interval property measures how many milliseconds occur between the automatic, repeated execution of the Timer event. For example, an Interval property of 1000 would cause there to be a 1 second delay between Timer events.
• A timer object has an Enabled property which can be set to either True or False. If this property is True, then the timer object's Timer event will execute.
• Code that is written in a timer object's Timer event will execute at regular intervals defined by the timer object's Interval property.
• The proper prefix to be used in a timer object's Name property is tmr.
• A timer object can be used to cause animation.
• Here is an example Timer event procedure that would cause animation of a shape object:
  
  Private Sub tmrShape1_Timer()

     If (shpShape1.Top < frmMain.ScaleTop) Then
        shpShape1.Top = frmMain.ScaleHeight
     End If
  
     shpShape1.Top = shpShape1.Top - 1
  
  End Sub
  
  If the Interval property of the timer object tmrShape1 is set to the value of 1 (i.e. 1 millisecond), this code would cause the shpShape1 object to move very smoothly across the form. If the Interval property was set to 100 or 1000 it would appear to "jump" in increments across the screen.
  

Objective #8: Use control arrays.

• Remember that an array is a group of VB variables with the same name. It is also possible to have an array of controls such as text boxes. When you give more than one control with the same name, Visual Basic gives you the option of creating a control array. Within a control array, each individual control must have a different Index property. The Index property is sometimes called the subscript of the control.
  
  
• All of the controls in a control array share the same Click event procedure (as well as some other events specific to that type of control.) Then a programmer can take advantage of the Index parameter in the Click event procedure and use it with an If/ElseIf/Else statement or a Select Case statement to make the event procedure respond in different ways depending on which control in the control array was clicked.
  
  
• To create a control array, you first place a control such as a command button on the form using any technique. You should name the control immediately giving it a name such as cmdClick. Then, you copy and paste that control to place a second control on the form. VB will ask you if you wish to create a control array. If you click yes, then the a control array is formed with the names of the controls being cmdClick(0) and cmdClick(1).
  
  Or, you first create a control such as a command button and give it a name like cmdClick(0). You must actually type a zero in parentheses after the actual name of the command button. This causes all subsequent command buttons that are named cmdClick to automatically take the names cmdClick(1), cmdClick(2), cmdClick(3), etc. The first control in a control array should always have the Index property (i.e. subscript) of zero.
  
  
• Menu commands that have the same Name property form a menu control array. Each command must have the same Name property but they likely will have different captions. Each menu command in a menu control array responds to the same Click event. However, the Index parameter in the header of the Click event procedure can be used with a Select Case statement to efficiently program each of the menu commands with separate actions.
  
  
• A control array is simply a group of VB controls that have the same name. Remember, controls are objects that you can place on a form that such as command buttons, text boxes, and labels. In a control array, each control must be of the same class. That is, no matter how many controls are in a control array, they all have to be the same type of control, command buttons for example. You can not have both command buttons and text boxes in the same control array.
  
  
• Each of the controls in a control array can have unique properties though. Therefore, you could make the BackColor of one command button vbGreen and another's vbBlue but still expect the same Click event procedure to execute when either one is clicked.