Proxy Models

Overview

In the model/view framework, items of data supplied by a single model can be shared by any number of views, and each of these can possibly represent the same information in completely different ways. Custom views and delegates are effective ways to provide radically different representations of the same data. However, applications often need to provide conventional views onto processed versions of the same data, such as differently-sorted views onto a list of items.

Although it seems appropriate to perform sorting and filtering operations as internal functions of views, this approach does not allow multiple views to share the results of such potentially costly operations. The alternative approach, involving sorting within the model itself, leads to the similar problem where each view has to display items of data that are organized according to the most recent processing operation.

To solve this problem, the model/view framework uses proxy models to manage the information supplied between individual models and views. Proxy models are components that behave like ordinary models from the perspective of a view, and access data from source models on behalf of that view. The signals and slots used by the model/view framework ensure that each view is updated appropriately no matter how many proxy models are placed between itself and the source model.

        QSortFilterProxyModel *filterModel = new QSortFilterProxyModel(parent);
        filterModel->setSourceModel(stringListModel);

        QListView *filteredView = new QListView;
        filteredView->setModel(filterModel);