hsqml-0.3.5.1: Haskell binding for Qt Quick

Graphics.QML.Model

Description

Facility for working with Qt data models.

This module is a placeholder for the ability to freely define QML classes which implement the QAbstractItemModel interface and functions to interact with those models. This is not currently supported, but the functionality will be available in a future release.

HsQML does currently provide one mechanism for creating a Qt data model, the AutoListModel item. This item implements the QAbstractItemModel interface and provides a QML-side solution for generating a stateful Qt data model from a succession of JavaScript arrays.

The advantage of this over using the arrays directly is that, when the array changes, the AutoListModel can generate item add, remove, and change events based on the differences between the old and new arrays. An simple array binding, on the other hand, causes the entire model to be reset so that views lose their state, cannot animate changes, etc.

To use this facility, you must assign an AutoListModel item to the model property of a QML view such as a Repeater item. In turn, the source property of the AutoListModel must then be bound to an expression yielding the arrays you want to use. The AutoListModel can be imported from the HsQML.Model 1.0 module using an import statement in your QML script and it has several properties which can be set from QML as described below:

mode
Specifies how the model is updated when the source array changes. Possible values are:
AutoListModel.ByReset
The model is reset entirely (default).
AutoListModel.ByIndex
The elements in the old and new arrays are compared for equality and change signals are sent for any that aren't equal. If the length of the array has changed then elements will be added to or removed from the end of the list model.
AutoListModel.ByKey
The key function is applied to each element in the old and new arrays. According to the key, elements which exist in both the old and new arrays are moved to their new positions in the list model as necessary, elements which only exist in the new array are added, and ones which only existed in the old are removed. Where elements have been moved, the old and new values are compared for equality and change signals are sent for any that aren't equal. Unlike the other modes which only require linear time to process the arrays, if elements are reordered then this mode requires quadratic time in the worst case.
AutoListModel.ByKeyNoReorder
This is the same as the ByKey mode except that the model will not explicitly move elements to different positions, only remove and re-add them at their new location as necessary.
source
JavaScript array containing the elements for the model.
equalityTest
JavaScript function which takes two parameters, compares them for equality, and returns a boolean. This is used by all the modes except ByReset. If no function is set then the model will use the JavaScript equals operator by default.
keyFunction
JavaScript function which takes a single parameter and returns a string key for use by the ByKey and ByKeyNoReorder modes. If no function is set then the model will use JavaScript's string conversion by default.