PowerBuilder objects

The basic building blocks of a PowerScript target are objects:

These objects are described in more detail in the sections that follow.

The Application object is the entry point into an application. It is a discrete object that is saved in a PowerBuilder library (PBL file), just like a window, menu, function, or DataWindow object.

The Application object defines application-level behavior, such as which fonts are used by default for text, and what processing should occur when the application begins and ends.

When a user runs the application, an Open event is triggered in the Application object. The script you write for the Open event initiates the activity in the application. When the user ends the application, the Close event in the Application object is triggered.

The script you write for the Close event typically does all the cleanup required, such as closing a database or writing to a preferences file. If there are serious errors during execution that are not caught using PowerBuilder’s exception handling mechanism, the Application object’s SystemError event is triggered.

Windows are the primary interface between the user and a PowerBuilder application. Windows can display information, request information from a user, and respond to the user’s mouse or keyboard actions.

A window consists of:

• Properties that define the window’s appearance and behavior (for example, a window might have a title bar and a Minimize box)

• Events triggered by user actions

• Controls placed in the window

Windows can have various kinds of controls, as illustrated in the following picture:

On the left of the window is a DataWindow control with horizontal and vertical trackbars. On the right is a group box that contains static text controls (containing descriptive labels), edit mask controls (as they appear when the SpinControl property is on), a check box, and two smaller group boxes with radio buttons. Under the main group box is a command button.

A DataWindow object is an object that you use to retrieve and manipulate data from a relational database or other data source (such as an Excel worksheet or dBASE file).

There are many ways to enhance the presentation and manipulation of data in a DataWindow object. For example, you can include computed fields, pictures, and graphs that are tied directly to the data retrieved by the DataWindow.

For example:

• If a column can take only a small number of mutually exclusive values, you can have the data appear as radio buttons in a DataWindow so users know what their choices are.

  

• If the data includes phone numbers, salaries, and dates, you can format the display to suit the data.

  

• If a column can take numbers only in a specific range, you can specify a simple validation rule for the data. This can spare you from writing code to make sure users enter valid data.

Menus are lists of items that a user can select from a menu bar for the active window. The items on a menu are usually related. They provide the user with commands (such as Open and Save As on the PowerBuilder File menu) or alternate ways of performing a task (for example, the items on the Edit menu in the Window painter correspond to buttons in the PainterBar).

You can select menu items with the mouse or with the keyboard, or use accelerator (mnemonic access) keys defined for the items. You can define your own keyboard shortcuts for any PowerBuilder menu item from a dialog box that you open with the Tools>Keyboard Shortcuts menu item.

A drop-down menu is a menu under an item in the menu bar. A cascading menu is a menu that appears to the side of an item in a drop-down menu.

Each choice in a menu is defined as a Menu object in PowerBuilder. The preceding window shows two Menu objects on the menu bar (File and Data), three Menu objects on the drop-down Data menu (Update, Delete, and Cancel), and two Menu objects on the cascading menu beside Update (Current Row and All Rows).

PowerBuilder lets you define two types of functions:

• Object-level functions are defined for a particular type of window, menu, or other object type and are encapsulated within the object for which they are defined. These are further divided into system functions (functions that are always available for objects of a certain object class) and user-defined functions.

• Global functions are not encapsulated within another object, but instead are stored as independent objects.

  Unlike object-level functions, global functions do not act on particular instances of an object. Instead, they perform general-purpose processing such as mathematical calculations or string handling.

A query is a SQL statement that is saved with a name so that it can be used repeatedly as the data source for a DataWindow object. Queries enhance developer productivity, because they can be coded once but reused as often as necessary.

A structure is a collection of one or more related variables of the same or different data types grouped under a single name. In some languages, such as Pascal and COBOL, structures are called records.

Structures allow you to refer to related entities as a unit rather than individually. For example, you can define the user’s ID, address, access level, and a picture (bitmap) of the employee as a structure called user_struct, and then refer to this collection of variables as user_struct.

There are two kinds of structures:

• Object-level structures are associated with a particular type of object such as a window or menu. These structures can always be used in scripts for the object itself. You can also choose to make the structures accessible from other scripts.

• Global structures are not associated with any object or type of object in an application. You can declare an instance of the structure and reference it in any script in an application.

Applications often have features in common. For example, several applications might have a Close button that performs a certain set of operations and then closes the window, or they might have DataWindow controls that perform the same type of error checking. Several applications might all require a standard file viewer.

If you find yourself using the same application feature repeatedly, you should define a user object. You define the user object once and use it as many times as you need.

User objects can be visual or nonvisual. They can be further divided into standard or custom user objects. Standard user objects, whether visual or nonvisual, are system objects that are always available with PowerBuilder. You can also use controls for external visual objects that were created outside PowerBuilder. The main types of user objects are:

You save objects, such as windows and menus, in PowerBuilder libraries (PBL files). When you run an application, PowerBuilder retrieves the objects from the library. Applications can use as many libraries as you want. When you create an application, you specify which libraries it uses.

You can create Project objects that build executable applications and components you can deploy to a server, as well as proxy objects you use in EAServer applications.