The basic design is that the application has a global undo context. When an operation which should be undoable occurs, you start the context, add as many undoables as required, and then end the context. Allowing a single undoable action to consist of multiple undoables lets the application reuse fine-grained logic to build coarse user-level actions (in Tasks this is used to build the Remove Completed action from multiple Delete Task actions). To make integrating this into applications even easier, I wrote a GtkAction which reflects the state of an undo context, so it is trivial to add redo/undo to the interface.

There is one remaining task left before this is ready to be released: undo support in the edit dialog entries. Once this is done, the next release of Tasks will be announced. I also plan to work with Iain on cleaning up this code and submitting it for inclusion into GTK+.

NP: Money Jungle, Duke Ellington, Charles Mingus, Max Roach