16.10 Using the Context Manager

The context manager provides a way of associating data with an X resource ID (mostly typically a window) in your program. Note that this is local to your program; the data is not stored in the server on a property list. Any amount of data in any number of pieces can be associated with a resource ID, and each piece of data has a type associated with it. The context manager requires knowledge of the resource ID and type to store or retrieve data.

Essentially, the context manager can be viewed as a two-dimensional, sparse array: one dimension is subscripted by the X resource ID and the other by a context type field. Each entry in the array contains a pointer to the data. Xlib provides context management functions with which you can save data values, get data values, delete entries, and create a unique context type. The symbols used are in X11/Xutil.h.

To save a data value that corresponds to a resource ID and context type, use XSaveContext().

To get the data associated with a resource ID and type, use XFindContext().

To delete an entry for a given resource ID and type, use XDeleteContext().

To create a unique context type that may be used in subsequent calls to XSaveContext() and XFindContext(), use XUniqueContext().

Christophe Tronche, ch@tronche.com