Adding custom widgets to model-driven GUI generation

For usable and acceptable Graphical User Interfaces (GUIs) in practice, predefined widgets of some given toolkit are often insufficient. An example is flight booking, where special widgets for selecting seats are common in today's applications. Model-driven GUI generation uses predefined widgets as building blocks, and also needs to include such special widgets customized for a given application. The problem is how to allow a GUI designer other than a framework developer to include such special widgets in the automated generation process. In this paper, we present a new approach for adding such special widgets to model-driven GUI generation. It does so by including custom widgets already during the automated generation, in order to make the result persistent also in case of re-generation. We explain our extensions to a generation framework for that purpose, so that a GUI designer using it for automated GUI generation can integrate custom widgets into the generated GUI, without having its source code or in-depth knowledge of the generation framework. This involves specifying them in Custom Widget Templates including design-time variability, so that they can be integrated in the design-time generation process starting from the highest level of abstraction.