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PxPlus COM Support |
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The COM interface in PxPlus allows developers to integrate external components produced by third-party vendors into their PxPlus applications in MS Windows. It provides convenient syntax for obtaining information about, as well as access to, the internal properties and methods of a Component Object Model (COM) object. This functionality is carried out via the COM automation standard, which is an implementation of the IDispatch interface in Windows. (This was commonly known as OLE automation in earlier Windows versions.)
When an application or library supports automation, the objects exposed by the application can be accessed through the PxPlus COM interface and manipulated to invoke their methods and get or set their properties. For example, a spreadsheet application might expose a worksheet, chart, cell, or range of cells, each as a different type of object, and a word processor might expose objects, such as applications, documents, paragraphs, bookmarks or sentences.
The following terms/definitions apply to automation and the PxPlus COM interface:
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Control |
An object that exposes a user interface; e.g., a dialogue with OK and Cancel buttons can be implemented as a control. These are now typically based on ActiveX vs. the older OLE control technology (OCX). |
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Object |
Any item that can be programmed, manipulated or controlled. Interfacing with an object is done through property setting and getting, and calling of methods. |
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Property |
A property is a characteristic of an object (an adjective); e.g. properties of Textbox might include: Name, Visible, Forecolor, etc. |
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Method |
A function that performs an action on an object (a verb). For example, an Application object might expose a Close method. |
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Instantiation |
To create an instance of (instantiate, define, name) an object. |
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Binding |
The process of connecting property and method calls to an object. |
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Late Binding |
Obtaining a reference to an object without any prior information about the object. Property and method names are resolved at run time. This is the binding style used by PxPlus. |
To program against an object, a reference to that object must first be obtained. This process is commonly referred to as binding. Unlike other languages, PxPlus simplifies this process by providing one statement that can be used to create new objects, reference running objects, and connect to remote objects.
Communication between an application and a COM object is performed either by reading or writing the object's properties or by invoking methods within the object. The PxPlus apostrophe operator (also known as tick) is used to access properties within a COM object and invoke its methods. See Accessing an Object's Properties and Methods.
The PxPlus commands used in the handling of COM objects are as follows:
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DEF OBJECT |
Directive used to create a new instance of a COM object. See Referencing a COM Object. |
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DELETE OBJECT |
Directive used to disconnect from a COM object. See Releasing an Object Reference. |
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DROP OBJECT |
Alternative to DELETE OBJECT directive. The two directives may be used interchangeably in PxPlus applications. |
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ON EVENT |
Directive used to process COM control events in a PxPlus application. See Event-Driven COM. |
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FUNCTION |
Directive supports the FOR EVENT keywords for setting a method to be processed for a particular incoming event. See Event-Driven COM. |