Overview of Qt's Undo Framework

Concepts

The following concepts are supported by the framework:

• Clean state: Used to signal when the document enters and leaves a state that has been saved to disk. This is typically used to disable or enable the save actions, and to update the document's title bar.
• Command compression: Used to compress sequences of commands into a single command. For example: In a text editor, the commands that insert individual characters into the document can be compressed into a single command that inserts whole sections of text. These bigger changes are more convenient for the user to undo and redo.
• Command macros: A sequence of commands, all of which are undone or redone in one step. These simplify the task of writing an application, since a set of simpler commands can be composed into more complex commands. For example, a command that moves a set of selected objects in a document can be created by combining a set of commands, each of which moves a single object.

QUndoStack provides convenient undo and redo QAction objects that can be inserted into a menu or a toolbar. The text properties of these actions always reflect what command will be undone or redone when they are triggered. Similarly, QUndoGroup provides undo and redo actions that always behave like the undo and redo actions of the active stack.