wx.lib.docview.Command

Command is a base class for modelling an application command, which is an action usually performed by selecting a menu item, pressing a toolbar button or any other means provided by the application to change the data or view.

Class Hierarchy

Inheritance diagram for class Command:

Known Superclasses

wx.Object

Methods Summary

__init__	Constructor. Command is an abstract class, so you will need to
CanUndo	Returns True if the command can be undone, false otherwise.
Do	Override this member function to execute the appropriate action when
GetName	Returns the command name.
Undo	Override this member function to un-execute a previous Do.

Class API

class Command(wx.Object)

Command is a base class for modelling an application command, which is an action usually performed by selecting a menu item, pressing a toolbar button or any other means provided by the application to change the data or view.

Methods

__init__(self, canUndo = False, name = None)

Constructor. Command is an abstract class, so you will need to derive a new class and call this constructor from your own constructor.

canUndo tells the command processor whether this command is undo-able. You can achieve the same functionality by overriding the CanUndo member function (if for example the criteria for undoability is context- dependent).

name must be supplied for the command processor to display the command name in the application’s edit menu.

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CanUndo(self)

Returns True if the command can be undone, false otherwise.

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Do(self)

Override this member function to execute the appropriate action when called. Return True to indicate that the action has taken place, false otherwise. Returning false will indicate to the command processor that the action is not undoable and should not be added to the command history.

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GetName(self)

Returns the command name.

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Undo(self)

Override this member function to un-execute a previous Do. Return True to indicate that the action has taken place, False otherwise. Returning False will indicate to the command processor that the action is not redoable and no change should be made to the command history.

How you implement this command is totally application dependent, but typical strategies include:

Perform an inverse operation on the last modified piece of data in the document. When redone, a copy of data stored in command is pasted back or some operation reapplied. This relies on the fact that you know the ordering of Undos; the user can never Undo at an arbitrary position in he command history.

Restore the entire document state (perhaps using document transactioning). Potentially very inefficient, but possibly easier to code if the user interface and data are complex, and an ‘inverse execute’ operation is hard to write.