Substitute Application Classes for System Classes

Applies To: Microsoft Dynamics AX 2012 R3, Microsoft Dynamics AX 2012 R2, Microsoft Dynamics AX 2012 Feature Pack, Microsoft Dynamics AX 2012

You should call the substitute application classes instead of calling the system classes that they extend.

In the Application Object Tree (AOT) under System Documentation > Classes there are several kernel or system classes whose names begin with a lowercase x. Examples of the x system classes include xApplication and xVersionControl. Some of the x system classes are extended by X++ application classes which are under AOT > Classes. For example, the Application X++ class extends the xApplication system class.

The X++ classes that derive from the x system classes are called substitute application classes. In the AOT under the Classes node, the icon next to the substitute application classes differs from the standard icon.

Special X++ Global Variables

Some of the substitute application classes that extend an x system class are associated with a special X++ global variable that represents an instance of the X++ class. For example, the appl variable references a pre-instantiated object from the Application X++ class. The advantage of the appl variable is that the system maintains the object throughout the scope of your session. It would be less efficient for your X++ code to repeatedly use the new Application() syntax to obtain an instance of the Application X++ class.

You should not use the xApplication system class. Use the Application substitute application class instead. You can reference the static members of the Application X++ class by using the standard syntax Application::checkForNewBatchJobs(). But you should reference the instance members of the Application class by using its corresponding special system variable appl, if one exists. This pattern applies to most of the x system classes. The Session substitute application class is one exception to this pattern, because there is no special system variable for Session.

The following table lists x system classes for which there is a corresponding substitute application class. The special X++ global variables are also shown for those classes that have one.

Example X++ Job that Uses Special Variables

The following X++ job demonstrates the syntax for using several special X++ variables that reference instances of the substitute application classes.

    static void UseSpecialSystemVariablesForXJob(Args _a)
    {
        TreeNode treeNode2;
        Args     args3;
        FormRun  formRun4;
        
        // appl variable
        print appl.buildNo();
     
        // company variable
        appl.company().reloadRights(); // referenced through appl
     
        // Infolog variable
        treeNode2 = infolog.findNode("\\forms\\custTable");
        print treeNode2.AOTgetProperty("Name");
     
        pause; // do want to continue
        
        // classFactory variable
        args3 = new Args(formstr(vendTable));
        formRun4 = classFactory.formRunClass(args3);
        formRun4.init();
        formRun4.run();
        formRun4.detach();
     
        Global::info("Job is ending. This is a message in the Infolog.");
        pause;
    }

See also

Microsoft Dynamics AX Class Overview

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