This chapter focuses on processing input from another source in the user interface: menu commands and dialog boxes. In this chapter, you will learn how to:
- Add menus to your programs by using the Menu Editor.
- Process menu choices by using program code.
- Use the CommonDialog ActiveX control to display standard dialog boxes.
Creating Menus
Menus, which are located on the menu bar of a form, contain a list of related commands. When you click a menu title in a Windows-based program, a list of menu commands should always appear in a well-organized list.
Most menu commands run immediately after they are clicked. For example, when the user clicks the Edit menu Copy command, Windows immediately copies information to the Clipboard. However, if ellipsis points (…) follow the menu command, Visual Basic displays a dialog box that requests more information before the command is carried out.
This section includes the following topics:
- Using the Menu Editor
- Adding Access and Shortcut Keys
- Processing Menu Choices
Using The Menu Editor
The Menu Editor is a Visual Basic dialog box that manages menus in your programs. With the Menu Editor, you can:
- Add new menus
- Modify and reorder existing menus
- Delete old menus
- Add special effects to your menus, such as access keys, check marks, and keyboard
- Shortcuts.
Creating Menu Command Lists
To build lists of menu commands, you first need to create the menus and then add them to the program menu bar.
To create a list of menu commands on a form
1. Click the form itself (not an object on the form).
2. On the Visual Basic toolbar, click the Menu Editor icon, or select Menu Editor from the Tools menu.
3. In the Caption text box, type the menu caption (the name that will appear on the menu bar), and then press TAB.
4. In the Name text box, type the menu name (the name the menu has in the program code). By convention, programmers use the mnu object name prefix to identify both menus and menu commands.
5. To add the menu to your program menu bar, click Next. The Menu Editor clears the dialog box for the next menu item. As you build your menus, the structure of the menus and commands appear at the bottom of the dialog box.
6. In the Caption text box, type the caption of your first menu command.
7. Press tab, and then type the object name of the command in the Name text box.
8. With this first command highlighted in the menu list box, click the right arrow button in the
Menu Editor. In the Menu list box, the command moves one indent (four spaces) to the right. Click the right arrow button in the Menu Editor dialog box to move items to the right, and click the left arrow button to move items to the left.
9. Click Next, and then continue to add commands to your menu.
The position of list box items determines what they are:
List box Item Position
Menu Title Flush left
Menu Command One indent
Submenu Title Two indents
Submenu Command Three indents
To add more menus
1. When you’re ready to add another menu, click the left arrow button to make the menu flush left in the Menu list box.
2. To add another menu and menu commands, repeat Steps 3 through 9 in the preceding procedure.
3. When you’re finished entering menus and commands, click OK to close the Menu Editor. (Don’t accidentally click Cancel or all your menu work will be lost.) The Menu Editor closes, and your form appears in the programming environment with the menus you created.
Adding Event Procedures
After you add menus to your form, you can use event procedures to process the menu commands. Clicking a menu command on the form in the programming environment displays the event procedure that runs when the menu command is chosen. You’ll learn how to create event procedures that process menu selections in Processing Menu Choices.
Adding Access and Shortcut Keys
Visual Basic makes it easy to provide access key and shortcut key support for menus and menu commands.
Access and Shortcut Keys
The access key for a command is the letter the user can press to execute the command when the menu is open. The shortcut key is the key combination the user can press to run the command without opening the menu. Here's a quick look at how to add access and shortcut keys to existing menu items:
Add an access key to a menu item Start the Menu Editor. Prefix the access key letter in the menu item caption with an ampersand (&). Add a shortcut key to a menu command Start the Menu Editor. Highlight the command in the menu list box. Pick a key combination from the Shortcut drop-down list box.
Creating Access and Shortcut Keys
You can create access keys and shortcut keys either when you first create your menu commands or at a later time. The following illustration shows the menu commands associated with two menus, File and Clock. Each menu item has an access key ampersand character, and the Time and Date commands area ssigned shortcut keys. See figure below.
After you place menu items on the menu bar, they become objects in the program. To make the menu objects do meaningful work, you need to write event procedures for them. Typically, menu event procedures:
- Contain program statements that display or process information on a form.
- Modify one or more object properties.
For example, the event procedure for a command named Time might use the Time keyword to display the current system time in a text box. Processing the selected command might require additional information (you might need to open a file on disk, for example). If so, you can display a dialog box to receive user input by using a common dialog box. You’ll learn this technique in the next section.
Disabling a Menu Command
In a typical Windows application, not all menu commands are available at the same time. In a typical Edit menu, for example, the Paste command is available only when there is data on the Clipboard. When a command is disabled, it appears in dimmed (gray) type on the menu bar. You can disable a menu item by:
- ® Clearing the Enabled check box for that menu item in the Menu Editor.
- ® Using program code to set the item's Enable property to False. (When you’re ready to use the menu command again, set its Enable property to True.)
Creating Dialog Boxes
A dialog box is simply a form in a program that contains input controls designed to receive information. To make your programming faster, Visual Basic includes an ActiveX control, named CommonDialog. With this control, you can easily display six standard dialog boxes in your programs. These dialog boxes handle routine tasks such as opening files, saving files, and picking fonts. If the dialog box you want to use is not included in this ready-made collection of objects, you can create a new one by adding a second form to your program. This section includes the following topics:
- Using the CommonDialog Control
- Common Dialog Object Event Procedures
Using the Common Dialog Control
Before you can use the CommonDialog control, you need to verify that it is in your toolbox. If you don’t see the CommonDialog icon, follow this procedure to add it to the toolbox.
To add the CommonDialog control to the toolbox
1. From the Project menu, click Components.
2. Click the Controls tab.
3. Ensure that the Selected Items Only box is not checked.
4. Place a check mark next to Microsoft Common Dialog Control, and then click OK.
Creating a Dialog Box
Follow this procedure to create a dialog box with the CommonDialog control.
To create a common dialog object on your form
1. In the toolbox, double-click the CommonDialog control.
2. When the common dialog object appears on your form, drag it to an out -of-the-way location.
Note: You cannot resize a common dialog object, and it disappears when your program runs. The common dialog object itself displays nothing — its only purpose is to display a standard dialog box on the screen when you use a method in program code to request it.
This table lists the name and purpose of the six standard dialog boxes that the common dialog object provides and the methods you use to display them:
Common Dialog Object event Procedures
To display a standard dialog box in a program, you need to call the common dialog object. You do this by using the appropriate object method in an event procedure. If necessary, you also use program code to set one or more common dialog object properties before the call. (For example, if you are using the Open dialog box, you might want to control what type of files is displayed in the list box.) Finally, your event procedure needs to process the choices made by the user when they complete the standard dialog box. This section presents two simple event procedures, one that manages an Open dialog box and one that uses information received from a Color dialog box.
The following topics are included in this section:
- Creating an Open Dialog Box
- Creating a Color Dialog Box
Creating an Open Dialog Box
The following code window shows an event procedure named mnuOpenItem_Click. You can use this event procedure to display an Open dialog box when the user clicks the Open command on the File menu. The event procedure assumes that you have already created a File menu containing Open and Close commands and that you want to open Windows metafiles (.wmf). See the piece of code given below.
Private Sub mnuOpenItem_Click()
CommonDialog1.Filter = "Metafiles (*.WMF)|*.WMF"
CommonDialog1.ShowOpen
Image1.Picture = LoadPicture(CommonDialog1.FileName)
mnuCloseItem.Enabled = True
End Sub
The event procedure uses these properties and methods:
Creating a Color Dialog Box
If you need to update the color of a user interface element while your program runs, you can prompt the user to pick a new color with the Color dialog box displayed by using the Common Dialog object. The color selections provided by the Color dialog box are controlled by the Flags property, and the Color dialog box is displayed with the ShowColor method.
This code window shows an event procedure that you can use to change the color of a label while your program runs. The value used for the Flags property — which in this case prompts Visual Basic to display a standard palette of color selections — is a hexadecimal (base 16) number. (To see a list of other potential values for the Flags property, search for CommonDialog constants in the Visual Basic online Help.) The event procedure assumes that you have already created a menu command named TextColor with the Menu Editor. See the code given below
Private Sub mnuTextColorItem_Click()
CommonDialog1.Flags = &H1&
CommonDialog1.ShowColor
Label1.ForeColor = CommonDialog1.Color
End Sub
The figure below shows the color dialog box.
EXERCISE: Creating a File Menu and Common Dialog Object Step by Step
In this exercise, you use the Menu Editor to create a File menu with Open, Close , and Exit commands for your program. You also assign access keys and shortcut keys to the commands, so you can run them from the keyboard.
To create a File menu
1. Start Visual Basic and open a new, standard Visual Basic application.
2. On the toolbar, click Menu Editor to open the Menu Editor dialog box.
3. In the Caption text box, type &File.
4. In the Name text box, type mnuFile, and then click Next.
By placing the & character before the letter F, you specify F as the menu access key.
To assign access and shortcut keys
1. In the Caption text box, type &Open….
2. In the Name text box, type mnuOpenItem.
3. To indent the selected (highlighted) command, click the right arrow button.
4. In the Shortcut drop-down list, click CTRL+O for a shortcut key, and then click Next.
5. In the Caption text box, type &Close.
6. In the Name text box, type mnuCloseItem.
7. In the Shortcut drop-down list, click CTRL+C for a shortcut key, and then click Next.
8. In the Caption text box, type E&xit.
9. In the Name text box, type mnuExitItem.
10. In the Shortcut drop-down list, click CTRL+X for a shortcut key, and then click OK.
To save your project
1. From the File menu, click Save Project As.
2. Save your form and project to disk under the name “Picture”. Visual Basic will prompt you for two file names — one for your form file (Picture.frm), and one for your project file (Picture.vbp).
To create a common dialog object
1. Verify that the CommonDialog control is in your project toolbox. If it isn't, add it now by using the Project menu Components command.
2. To add a common dialog object to your form, double-click the CommonDialog control in the toolbox, and then drag the object to the lower right-hand side of the form.
To create the image object
1. Click the Image control and create a large image object in the middle of your form. When you run your program, the image object displays picture files with *.jpg extension on a form.
2. On the form, click Image1. To restore the Properties window to full size, double-click the Properties window title bar.
If you cannot see the Properties window, click Properties on the toolbar to display it.
3. Click the Stretch property and set it to True.
When you run your program, Stretch makes the metafile fill the entire image object.
4. On the toolbar, click Save Project to save these changes to your program.
To write event procedures
1. In the Project window, click View Code , click the Code window Object drop-down list box, and then click mnuOpenItem.
2. In the mnuOpenItem_Click event procedure, type the following code:
CommonDialog1.Filter = "JPEG FILES (*.JPG)|*.JPG"
CommonDialog1.ShowOpen
Image1.Picture = LoadPicture(CommonDialog1.Filename)
mnuCloseItem.Enabled = True
3. In the Object drop-down list box, click mnuCloseItem, and then type the following code:
Image1.Picture = LoadPicture("")
mnuCloseItem.Enabled = False
4. In the Object drop-down list box, click mnuExitItem, and then type End in the event
procedure.
5. On the toolbar, click Save Project to save your changes.
To run the program
1. On the Visual Basic toolbar, click Start.
Visual Basic loads the program and the form with its File menu.
2. From the File menu, click Open.
3. When the Open dialog box appears, load a picture file from your computer.
The picture selected should appear correctly sized in your image object.
4. From the File menu, click Close.
Your program should clear the picture file and turn off the Close command.
5. Try using the access keys and the shortcut keys to run the File menu commands. When you’re finished, click the File menu Exit command.
Source: EASTERN MEDITERRANEAN UNIVERSITY FACULTY OF ENGINEERING MECHANICAL ENGINEERING DEPARTMENT
