Graphical User Interface (GUI)

• Graphical user interface presents a pictorial interface to a program. It gives a program a distinctive “look” and “feel”.  
  
• User friendly GUIs allow the user to spend less time trying to remember keystroke sequences, and be more productive.  
  
• GUIs are built from controls which are objects the user interacts with via the mouse and keyboard.  

 Controls 

• Controls are reusable, predefined components used for visual programming.  
  
• Controls serve as building blocks that can be quickly combined to create a working application.  

Intrinsic Controls and ActiveX Controls 

• Intrinsic controls (standard controls) are the default controls provided in the Visual Basic toolbox. The following are a list of intrinsic controls:

• ActiveX controls must be loaded into the Visual Basic projects with the Components dialog. Components dialog is displayed when Project à Components menu item is select.  
  
• Once the active control is loaded, an icon representing the control is added to the tool bar.  
  
• Other than the loading process, ActiveX controls are used in the same manner as intrinsic controls (with properties, methods, and event procedures.)  
  
• Many independent software venders specialize in creating ActiveX controls for sale.  

Some Frequently Used Standard Controls  

• Throughout the assignments, we have exercised many standard controls such as CommandButton, Label, ListBox, PictureBox, and TextBox.  
  
• In the following, we introduce some other frequently used controls such as ComboBox, CheckBox, OptionButton and Timer.

ComboBox 

• Combines TextBox features with a short drop down list.  
  
• ComboBox has three different styles (Style property):
• Dropdown Combo – the default style that allow the user to type data directly into the ComboBox as well as select items from the drop down list. (constant: VbComboDropDown)
  
• Simple Combo – appears as a TextBox with no drop down list. (constant: VbComboSimple)
  
• Dropdown List – require the user to select items from the drop down list.  Does not allow the user to enter data directly. (constant: VbComboDropDownList)

• Some ComboBox Properties:
• ListCount – number of drop-down list items.
• ListIndex – The index of the selected item.  If no item is selected, ListIndex is -1.
• NewIndex – The index of the last item added to the ComboBox.  
  
• To add item to a ComboBox:
• Call cboCombo.AddItem(txtInput.Text)  
  
• To remove item from a ComboBox:
• Call cboCombo.RemoveItem(cboCombo.ListIndex)  
  
• To clear all items in a ComboBox:
• cboCombo.Clear  
  
• To display an item in the ComboBox:
• cboCombo.Text = txtInput.Text  
  
• See example (p.421, Fig-10.17).  

CheckBox  

• A CheckBox control displays a  a when selected; the a disappears when the CheckBox is cleared.  It acts as a toggle box for the user to check.  
  
• Commonly used to express optional features.  If checked, the feature is used.  
  
• A CheckBox’s Value property determines whether a CheckBox is checked (vbChecked or 1), or unchecked (vbUnChecked or 0).  
  
• Example:

If chkPreserve.Value = vbChecked Then  
    …  
Else  
    …  
EndIf

OptionButton  

• OptionButton controls are used in an option group to display options from which the user selects only one.  
  
• You group OptionButton controls by drawing them inside a container such as a Frame control, a PictureBox control, or a Form.  
  
• All OptionButton controls within the same container act as a single group.  
  
• When a user selects an OptionButton, the other OptionButton controls in the same group are automatically unavailable.  
  
• Fig 10.41 demonstrates function MsgBox using OptionButtons.  

Timer  

• A Timer control can execute code at regular intervals by causing a Timer event.  
  
• After the time specified in the Interval property (number of milliseconds) has elapsed, VB calls the Timer’s Timer event procedure.  
  
• The Timer control, invisible to the user, is useful for background processing.  
  
• Timers can be disabled by setting their Enabled property to False, and can be enabled by setting the Enabled property to True.  

Creating a Menu System  

• Command buttons and menus are the principal mechanisms by which the user explicitly requests that some processing take place.  
  
• Menus provide a list of functions on the main form without cluttering the screen.  
  
• Menus are like other controls, in that they have properties and events.  
  
• Menus are added to a form using the Menu Editor (Tools à Menu Editor).  

• Once a menu is created, its event can be viewed in the Code window.  
  
• Each menu item is treated as a separate object that has three frequently used properties (Checked, Enabled, Visible), and only one event (Click).  

• When a menu item is selected, VB executes the corresponding menu event procedure:  
  
• Example:

Private Sub MnuFile_Click( )

Steps for Defining a Menu Command  

1. Select a menu command in the list. The last item in the list is always blank, so you can select it to add a new menu command.
   
2. Type a Caption for the menu command.  As with other controls, use an ampersand (&) to specify an access key.  (Note: If the Caption property is set to a hyphen, VB inserts a separator bar between the items.)
   
3. Type a Name property. Menu names should be prefixed with "mnu".  
   
4. If needed, assign a shortcut key by selecting one from the Shortcut drop­down combo box. Shortcut keys must be unique for all menu commands on the form.  
    
5. Set the Checked, Enabled, and/or Visible properties as necessary.
   
6. Specify the menu command's order in the menu hierarchy by using the arrow buttons.  
   
7. Repeat steps 1 through 6 for each menu command required.
   
8. Click the OK button to close the Menu Editor dialog.

Pop-up Menu  

• Pop-up menus are menus that appear when the user right-clicks the mouse.  
  
• Pop-up menus are created using the Menu Editor dialog with the Visible CheckBox unchecked. Once created, Call the method PopupMenu to display a pop-up menu.  
  
• For pop-up menus to work, the form must include a Menu control, which must have at least one submenu.
  
• Example (p. 438, Fig-10.35):  

Private Sub Form_MouseUp(Button As Integer, Shift As Integer, X As Single, Y As Single)  
        ' When right button is clicked display Pop Up menu  
        If Button = vbRightButton Then  
               Call PopupMenu(mnuPopUp)  
        End If
End Sub  

Private Sub mnuSub_Click( )
        ' Performs action associated with sub menu item
        lblOutput.Caption = "Sub"
End Sub

Message Box  

• You can display a message box that includes a custom dialog intended to provide the user with information.
• The MsgBox dialog can be customized to display a text message, a predefined icon, and predefined buttons. 
  

The figure below includes an example of a message box.  Note the different features that can be customized by the programmer.

• A message box can be displayed by using the MsgBox statement or the MsgBox( ) function.
• The MsgBox statement only displays a message box, while the MsgBox ( ) function displays a message box and returns a value.
• The simplified syntax for the MsgBox statement is
  •       MsgBox strMessage [, TypeOfBox][, strTitle]
• The simplified syntax for the MsgBox ( ) function is
  •       intReturn = MsgBox (strMessage [, TypeOfBox][, strTitle])

--------------------------

The TypeOfBox is determined by combining different groups of built-in integer constants.

TypeOfBox = ButtonType + IconType + ModalType + DefaultButton

The button type allows the programmer to specify the number and type of buttons that appear on the message box.   

The icon type allows the programmer to choose between four different types of icons to display in the message box.   

The modal type determines whether the user can can interact with other windows while the message box is displayed.  For application modal, the user cannot interact with other windows in the same application, but can still interact with other programs.  For system modal, the message box must be dismissed before any other action can take place in any application.

The default button is not shown in our text, but it allows the programmer to specify which button on the message box is the default.  

When the MsgBox function is used, it returns a value.  The table below lists the return values.     

Here is an example of the MsgBox statement: 

typeOfBox = vbOKOnly + vbInformation + vbApplicationModal
MsgBox "Enrollment recorded.", typeOfBox, "Status"

Here is an example of a MsgBox function call:

typeOfBox = vbOKCancel + vbExclamation + vbApplicationModal
response = MsgBox("OK to exit, Cancel to continue.", typeOfBox, "Exit")
If (response = vbOK) Then End        ' OK button pressed