Special Edition Using Visual FoxPro 6

Chapter 18

The Visual FoxPro Foundation Classes

• Familiarizing Yourself with the Visual FoxPro Foundation Classes
• How to Use the Visual FoxPro Foundation Classes
• Adding Visual FoxPro Foundation Classes to a Form Using the Component Gallery
• Adding Visual FoxPro Foundation Classes to a Form Using the Form Control Toolbar
• Adding Visual FoxPro Foundation Classes to a Project
• More Examples of Using the FoxPro Foundation Classes

Familiarizing Yourself with the Visual FoxPro Foundation Classes

This chapter introduces you to a new feature of Visual FoxPro 6, the Visual FoxPro Foundation Classes. One major advantage of adopting object-oriented programming (OOP) technology is that OOP promotes object reusability to facilitate rapid application development (RAD). The only problem is determining where to get the class objects to reuse. In the past, you could reuse class objects that you developed for previous tasks, borrow them from your friends, or buy them from a third-party source. The new Visual FoxPro Foundation Classes that ship with Visual FoxPro contain over 100 reusable classes that you can add to your application to speed up and simplify your development effort while reducing the amount of code you have to write.

The Visual FoxPro Foundation Classes consist of a group of classes that provide a wide range of operations that most typical applications need. The classes that are provided support the following functionality:

• Database manipulation and management operations
• Database concurrency resolution
• Custom extendable components
• Web page development
• Windows API support
• Other varied application support

The Visual FoxPro Foundation Classes are stored as .VCX class libraries. You can add foundation classes to your applications to provide powerful functionality with little or no programming. Furthermore, you are free to distribute the foundation classes with your applications.

You can even load them in the Class Browser or Class Designer and examine all the structures and code. Not only do you find out how the classes operate, but you also can learn some advanced Visual FoxPro programming techniques.

Table 18.1 describes what each of the foundation classes does and identifies the associated visual class library file (.VCX). You will learn how to use these foundation classes in your applications later in this chapter.

How to Use the Visual FoxPro Foundation Classes

Most of the FoxPro Foundation Classes are added directly to a form and require little or no coding. Classes with a base class of Form, Formset, or Toolbars can be added only to a project and run programmatically.

The simplest way to add a foundation class to your application is to drag and drop it from the Component Gallery to your form or Project Manager. You can also drag and drop a class from the Class Browser, Project Manager, and the Forms Control toolbar to your form. Although the process is not described until Chapter 19, "The Visual FoxPro Component Gallery," using foundation classes is exceptionally easy. All you have to do to run them is to select Tools, Component, and the Component Gallery is displayed as shown in Figure 18.1. Notice that the foundation classes are grouped into 14 categories. When you click on one of the categories, the corresponding classes appear in the right panel. You can click on one of the classes and a brief description appears in the bottom panel. If you want more information about a class, right-click on the class and choose Help from the shortcut menu.

Another advantage of using the Component Gallery as a source of foundation classes for forms and projects is that it regulates which classes can be transferred to a form or project. For example, you do not have to be concerned if the base class for a foundation class is a Form class when you attempt to insert it in a form. In addition, the Component Gallery provides an option of creating a subclass when foundation classes are inserted in a project.

Adding Visual FoxPro Foundation Classes to a Form Using the Component Gallery

Now you can build an application that illustrates how you can use the Component Gallery to add a foundation class to a form. You will use the Data Edit Buttons foundation class that provides navigation and editing support for the application. This control appeared in the right panel of Figure 18.1. Follow these steps to build the application:

Figure 18.1 : The Component Gallery showing the list of Foundation Classes categories in the left panel and the Button controls in the right panel.

1. Create a project called EmployeeList.
2. Highlight the Form folder in Project Manager, and click on New to create a new form. Name it Employee.scx.
3. Choose View, Data Environment.
4. Right-click on the Data Environment dialog box, and choose a table. In this case, choose the EMPLOYEE.DBF table.
5. Add a grid to the form. Use the Grid Builder to define the fields and headings. To use the Builder, right-click on the form, and choose the Builder item from the shortcut menu.
6. Set the form's Caption property to Employee List.
7. Drag the Data Edit Buttons control to the form, as shown in Figure 18.2.
   Figure 18.2 : The Data Edit Buttons class is dragged from the Component Gallery and dropped on the form.
8. Add the following three lines of code to the Refresh event of the Data Edit Buttons control:

        PICBTNS::Refresh
   
        NODEFAULT
   
        THISFORM.Grid1.SetFocus
   
   

9. Close the Form Designer, and name the form Employee.
10. Click the Project Manager Build button to compile and build the application.

Now you can execute the new Employee List application. The results are shown in Figure 18.3. The Data Edit Buttons object consists of 10 buttons: Top, Previous, Next, Bottom, Find, Print, Add, Delete, Edit, and Save. By adding a single control, you created a complete application that maintains the Employee table. You had to write three lines of code because the grid did not show the repositioned record pointer. The lines of code set the focus to the grid after the Data Edit Buttons object refreshes its display state. The NODEFAULT keyword suppresses the call to the default Refresh event because you already called it explicitly.

Figure 18.3 : The Employee List form application using the Data Edit Buttons object from the Visual FoxPro Foundation Classes.

You can also add a class to a form or a project by right-clicking on the class in the Component Gallery and choosing the Add to Form option from the shortcut menu, as shown in Figure 18.4. In this example, the ActiveX calendar is added to the Employee List form.

Figure 18.4 : The Component Gallery with its shortcut menu displayed.

Follow these steps to add a calendar to the Employee List form:

1. Open the Form Designer to modify the Employee List form. Then open the Component Gallery.
2. Right-click on the ActiveX Calendar class in the Component Gallery. Next, choose the Add to Form shortcut menu item.
3. As soon as the calendar object is placed on the form, the _OLECalendar1 Builder appears. Enter DateHired in the Field Name to Bind Calendar edit box, as shown in Figure 18.5.
   Figure 18.5 : The ActiveX Calendar Class Builder with the bound data field showing.
4. Rearrange and resize controls on the Employee List form as appropriate.
5. Add the following line of code to the Grid1.AfterRowColChange event:

   THISFORM._OLECalendar.RefreshDisplay

Each time the grid is moved to a new row or column, the Grid's AfterRowColChange event fires. At that time, the ActiveX Calendar's RefreshDisplay is called to update the calendar date and refresh the calendar display. The calendar date is updated from the bound DateHired field in the Employee table.

Now run the Employee List form and observe the results, as shown in Figure 18.6. Notice that when you move to a new row, the date in the calendar is the same as the grid's Date Hired field. This enhancement to the Employee List code took only one additional line of code. Imagine how many lines of code you would have to write to duplicate this example if you had to write it all from scratch.

Figure 18.6 : Results of running Employee List with a calendar added.

Adding Visual FoxPro Foundation Classes to a Form Using the Form Control Toolbar

You can add Visual FoxPro Foundation Classes from the Form Control toolbar, but first you have to add the visual class library file (.VCX) for your desired foundation class to your Form Control toolbar. The classes are all stored in the \VFP98\ffc directory. Table 18.2 lists the foundation categories and their associated visual class libraries.

1. Choose Tools, Options. Then click on the Controls tab. Next, choose the Add option, and a File Open dialog box appears.
2. Choose one of the visual class libraries from Table 18.2 from the \VFP98\ffc directory.
3. Click the Save as Default button if you want the control to remain on the Form Control toolbar for subsequent Visual FoxPro sessions.
4. Click the OK button to exit the options menu.

If you want the foundation class to remain on the Form Control toolbar only for the current Visual FoxPro session, click on the View Classes icon on the Form Control toolbar, and choose the Add option. A File Open dialog box then appears. Then choose one of the visual class libraries in Table 18.2.

After you place the desired foundation classes on the Form Control toolbar, you can drag and drop a foundation class from the Form Control toolbar to your form. For example, I added the Date/Time category foundation classes to the Form Control toolbar, as shown in Figure 18.7. You can drag and drop the Clock class (_clock) to the form (see Figure 18.7).

Figure 18.7 : Adding the Clock foundation class to a form on the Form Control toolbar.

If you run the enhanced Employee List form, it will appear as shown in Figure 18.8, complete with the date and time displayed, compliments of the clock object.

Figure 18.8 : The Employee List form displaying the date and time, compliments of the clock object.

Adding Visual FoxPro Foundation Classes to a Project

Just as you can add foundation classes to a form, you can also add them to a project. Usually, you add foundation classes to a form. However, foundation classes with a base class of Form, FormSet, or Toolbar can be added only to a project. For example, the About dialog class or a Splash Screen class must be added to a project. Then you add code to activate them.

The easiest and best way to add a foundation class to a project is to drag a class from the Component Gallery to the project or choose the Component Gallery shortcut menu's Add to Project item. Of course, you can use other ways. You can drag the visual class library file (.VCX) from the Windows Explorer to the project. Another way is to choose the Project Manager Add button to add the visual class library file to the project.

When you add the foundation class to the project using the Component Gallery, the Add Class to Project dialog box is displayed, as shown in Figure 18.9.

Figure 18.9 : The Add Class to Project dialog box is displayed when you add a foundation class to a project using the Component Gallery.

In this dialog box, you have three options. You can simply add the class to the project, create a new class derived from the selected class, or create a new form containing the class.

If you choose the Add Class to Project option, the visual class library file is added to the project. You should choose this option when you want to execute the foundation class programmatically, and you don't plan to enhance the functionality of the class.

If you want to change the foundation class's functionality, you can choose the Create New Class from Selected Class option. You are prompted to enter the name of the new class that is derived from the selected class. Then you can add code to modify the behavior of the class.

If you want to modify the appearance of the selected class's form, you can choose the Create New Form from Selected Class option. In this case, you are prompted to enter the name of the new form. Then you can modify the new form as you please.

Suppose you want to add an About box to the Employee List form. Here are the steps:

1. Open the EmployeeList project.
2. Drag the About box class from the Component Gallery to the EmployeeList project.
3. Choose the Create New Form from Selected Class option in the Add Class to Project dialog box.
4. When you are asked to name the new form, name it About.
5. After the Form Designer appears showing the new About form, change items on the form as appropriate. Figure 18.10 shows it with a Logo (.GIF) file added and some changes to labels and the Caption property.
   Figure 18.10: The Visual FoxPro Form Designer with the new About form open.
6. Modify the Employee List form, and add a command button to the form with the Caption property set to About.
7. Add the following line of code to the Click event for the About button:

   DO FORM ABOUT
   
   

8. Build and run the application. Figure 18.11 shows the new About command button on the Employee List form and the new About dialog box that results when you click this button.

Figure 18.11: The Employee List and About forms at runtime.

The next example illustrates how to add a splash screen to an application using the Splash Screen dialog class. The class will be executed programmatically to show the splash screen.

I added a program named EmployeeList.Prg to the EmployeeList project to display the splash screen before the Employee List dialog box activates. You don't need to add the Splash Screen class to the project because the _dialogs.vcx visual class library was added to the project when you added the About class. Follow these steps to create this example:

1. Open the EmployeeList project.
2. Click on the Programs folder, and click on the New button. A text edit window appears.
3. Enter the following code into the text window:

        oSplash = NewObject("_splash","_dialogs")
   
        IF VARTYPE(oSplash) = "O"
   
            oSplash.Picture = HOME()+"hlpglobe.gif"
   
            oSplash.nDuration= 5   && Set the duration to 5 seconds
   
            oSplash.Show()
   
        ENDIF
   
        DO FORM Employee
   
   

4. Save the program, and name it EmployeeList.prg.
5. Highlight the EmployeeList.prg program in the project, and choose Project, Set Main to make this program the main program instead of the Employee form.
6. Rebuild and run the application. The resulting splash screen is shown in Figure 18.12.

Figure 18.12: The EmployeeList application's splash screen.

You use the NewObject() function in this application to open the Splash Screen class in the _dialogs visual class library and save the object variable oSplash. Next, you assign new values to the splash screen's Picture and nDuration properties. Finally, you launch the splash screen by using the Show() method.

More Examples of Using the FoxPro Foundation Classes

To help you learn how to use the FoxPro Foundation Classes and other aspects of Visual FoxPro, Microsoft has supplied the Solutions application in the Samples directory. When you execute the Solutions application, a dialog box appears, as shown in Figure 18.13. You can choose an application from the outline list and either run it or look at the code to find out how it works.

Figure 18.13: The Solutions sample application dialog box.