The development of user interfaces for portable devices offers numerous challenges because of the heterogeneity of the environments in which mobile services are deployed. Thus, an adaptive middleware is needed to generate the user interfaces and adjust their parameters to the different usage scenarios. The middleware needs to enable the separation of the adaptation procedures from the core operations of the interaction. Furthermore, a more structured approach is required to describe the different aspects of the human-computer interaction, which can then be used by the middleware to generate adaptive user interfaces. Specifically, this paper describes the work-in-progress of a run-time middleware that enables the generation of user interfaces on portable devices based on a set of abstract models, and adapting them to the context-of-use. We also present a prototype mobile application to illustrate our approach.