New-style service constructors in OpenOffice.org Basic

Starting with OpenOffice.org 3.2 OpenOffice.org Basic allows to use UNO new-style service constructors (for more details please see http://wiki.services.openoffice.org/wiki/Documentation/DevGuide/ProUNO/Services).

To achieve this UNO services are now mapped to OpenOffice.org Basic objects. They have to be addressed by using the complete UNO namespace path. Let's take the example from the "Service Constructors" section in the wiki page mentioned above completed by a dummy module:

module com { module sun { module star { module foo {

service SomeService: XSomeInterface {

create1();

create2([in] long arg1, [in] string arg2);

create3([in] any... rest);

};

}; }; }; };

Then the service object can be addressed like this:

Dim oSomeServiceObj

oSomeServiceObj = com.sun.star.foo.SomeService

All constructors defined for a new-style service are available as methods of its corresponding OpenOffice.org Basic object, e.g.:

Dim oSomeInstance As Object

oSomeInstance = oSomeServiceObj.create1()

' or

oSomeInstance = oSomeServiceObj.create2( 42, "Hello" )

' or

oSomeInstance = oSomeServiceObj.create3( aVarOfAnyType )

Internally the parameters are passed to the createInstanceWithArgumentsAndContext method of com.sun.star.lang.XMultiComponentFactory as Arguments sequence. The UNO default context is used both to obtain the Multi Component Factory and as Context parameter.

This is the simple version. To give more control to the user there's also another way to call service constructors similar to the one used in the C++ mapping of service constructors. In this version the UNO context can be passed explicitly to the constructor method. Then the code would look like this:

Dim oMyContext As Object

oMyContext = GetContextFromSomewhere()

Dim oSomeInstance As Object

oSomeInstance = oSomeServiceObj.create1( oMyContext )

' or

oSomeInstance = oSomeServiceObj.create2( oMyContext, 42, "Hello" )

' or

oSomeInstance = oSomeServiceObj.create3( oMyContext, aVarOfAnyType )

In this case the passed context is used internally instead of the UNO default context.

The OpenOffice.org Basic runtime automatically chooses the appropriate version by checking the first parameter's type. If the first parameter supports com.sun.star.uno.XComponentContext and the parameter count exceeds the one of the used constructor the second version is used.

This can become a problem in one special case: If a constructor has a rest parameter and expects an object supporting XComponentContext as argument it becomes ambiguous which version should be used. It could be a call to the constructor with the intention to pass the context as an argument to the service (case 1) or with the intention to pass the context to createInstanceWithArgumentsAndContext with no argument for the service (case 2).

The solution: In case 1 it doesn't matter if no or one context is passed as parameter:

oSomeInstance = oSomeServiceObj.create3()

oSomeInstance = oSomeServiceObj.create3( oMyContext )

oMyContext is only used for createInstanceWithArgumentsAndContext and not passed as argument to the service.

For case 2 the context has to be passed twice

oSomeInstance = oSomeServiceObj.create3( oMyContext, oMyContext )

Then the second context parameter is passed to the service. This may look a little bit strange, but it's a rather exotic scenario anyway.

If a new-style service only has an implicit constructor it's mapped to a method "create" without parameters in OpenOffice.org Basic.

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