DESKTOP FRAMEWORKS CONCEPTS

Commands

Commands are objects that encapsulate a change to a target (the data upon which the command operates). Commands are instantiations of the TCommandOn<> template class. Instantiations of template classes are parameterized by the type of the target they act upon.

A command is capable of making a change to the target object (doing), reversing a change to a target (undoing), and remaking (redoing) the change to the target. This protocol includes checking preconditions, and notifying of any changes in the status of the preconditions.

A command can:

Detect if the preconditions for the change have been satisfied (CanDo).

Change the target (Do).

Change the target incrementally (DoBegin, DoEnd).

Reverse the change (Undo, Redo).

Make the change (Commit).

Operate polymorphically--copy and stream.

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