Grouping with the collection widgets
In this section, we will look at widgets that are designed to efficiently contain main widgets. Some of the widgets mentioned in the previous section do this, such as Form and Toolbar, but collection widgets support thousands of items (though they’re not all visible at one time). These widgets are commonly used for displaying a huge numbers of options or navigating complex datasets.
Due to the requirement that collection widgets only show large amounts of data, they are designed to only show a small portion of the possible widget at a time. To do this, and to maintain great performance, they have a caching mechanism that makes their API a little more complex than the widgets we have seen previously.
Callbacks
Each of these widgets relies on a number of callback functions. The first of these functions will provide information on the dimensions of the data that the widget will display (for a more complete discussion on data, see Chapter...
