I suggest people to use com.sun.star.awt.DialogProvider and its family to instantiate dialog from xdl file generated by Basic IDE dialog editor.
When the dialog instantiated by the dialog provider, dialog elements are wrapped by a wrapper class and it is delegated by the element and it also provides some properties such as PositionX, PositionY, Step and so on. Step properties are useful to make multistep dialog. If the dialog constructed by hand, these properties are not provided.
Even if someone want to add controls that can not be make using dialog editor of the Basic IDE, instantiate empty dialog from xdl file and create its elements with createInstance method of com.sun.star.lang.XMultiServiceFactory interface, its result is always wrapped by the wrapper mentioned above.
Here is a way to instantiate dialog from document embedded library using the dialog provider:
http://www.oooforum.org/forum/viewtopic ... highlight=
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Apache OpenOffice 4-dev on Xubuntu 14.04