The COM support has the following limitations:

• Only non-visual controls are supported. A control cannot be used to add graphical elements to a Microsoft Dynamics NAV object. For example, you cannot add a third-party control to a page. However, the control can display information and interact with the user in a window of its own.
  
• Exception handling is not supported. Information about exceptions cannot be retrieved from a control or automation server through the Invoke method of the IDispatch interface and the EXCEPINFO structure.
  
• Unlike Microsoft Dynamics NAV 2009, automation objects in Microsoft Dynamics NAV 2013 R2 cannot target the computer that is running the Microsoft Dynamics NAV Server. Only client-side automation objects are supported. Instead of implementing server-side automation object, you can use Microsoft .NET Framework Interoperability. For more information, see Extending Microsoft Dynamics NAV Using Microsoft .NET Framework Interoperability.
  

The mechanisms for calling methods in a control, passing parameters, and receiving return values are somewhat complex. Using tools such as the wizards in Microsoft Visual C++ shields you from most of the complexities. However, there is no one-to-one relationship between the data types that you can use when you implement methods in, for example, Visual C++ and the data types in C/AL. Some of the COM data types are not supported in C/AL and some have a limitation imposed on their usage.

When you use the C/AL Symbol Menu, you can see the syntax for a method or property that has the return value and the parameters shown with the COM data types.

Mapping C/AL Data Types to COM Data Types

Mapping COM Data Types to C/AL Data Types

Unsigned char (VT_UI1), SCODE (VT_ERROR), and SAFEARRAY (VT_ARRAY)

When you call a method with a ByRef parameter, the typical C/AL type conversions do not occur. For example, this means that if the parameter is of type float, you have to use a C/AL variable of type Decimal. You cannot use Integer and have C/AL convert it for you.

Note
If the value that you want to pass has the incorrect type, when, for example, it is a value from a database record field, then you can assign it to a C/AL variable of the correct type before you call the COM object method.

You will sometimes see a COM object method or a property in the C/AL Symbol Menu that has type IDispatch. This means that the method or property returns or expects a COM object. In this case, you must use a C/AL Automation variable that has been declared, through the Subtype, to be the correct COM object. You will have to study the documentation for the automation server to gain the necessary information.

You will also see properties and methods that do not have one of the expected types. For example, a method in Microsoft Office Excel can have a return value of type WORKBOOK. This means that the automation server has implemented a USERDEF type. Microsoft Dynamics NAV supports USERDEF types in two contexts: IDispatch and Enumeration.

If the USERDEF type is an IDispatch, it means that it is an interface (sometimes also called class or object) with a specific GUID. You will have to use the same object for a return value or parameter. You do this by creating an Automation variable with the correct subtype. For example, Microsoft Excel has several methods that return a WORKBOOK variable. This means that you must declare a variable of type Automation and subtype 'Microsoft Excel 8.0 Object Library'.Workbook.

If the USERDEF type is an enumeration, you cannot use the symbolic name, for example, xl3DPie, but instead must use the enumerator, for example, -4102. For Microsoft Office products, you can find this value by using the VBA Object Browser.

Reference

Concepts