Example of using the Memento Pattern in C#. More...

Collaboration diagram for Memento_Exercise:

Public Member Functions
void	Run ()
	Executes the example for the Memento Pattern in C#.

Private Member Functions
void	Memento_SaveForUndo (Memento_TextObject text, string operation)
	Take a snapshot of the given text object associated with the name of given operation.

void	Memento_Operation_Replace (Memento_TextObject source, string searchPattern, string replaceText)
	An operation to search and replace text in a Memento_TextObject.

void	Memento_Operation_Reverse (Memento_TextObject source)
	An operation to reverse the characters in the given Memento_TextObject.

void	Memento_Undo (Memento_TextObject text)
	Perform an undo on the given Command_TextObject, using the mementos in the "global" undo list. If the undo list is empty, nothing happens.

void	Memento_ApplyReplaceOperation (Memento_TextObject text, string searchPattern, string replaceText)
	Helper function to replace a pattern with another string in the given Memento_TextObject after adding a snapshot of the text object to the undo list. Finally, it shows off what was done.

void	Memento_ApplyReverseOperation (Memento_TextObject text)
	Helper function to reverse the order of the characters in the given Memento_TextObject after adding a snapshot of the text object to an undo list. Finally, it shows what was done.

Private Attributes
Stack< IMemento >	_mementoUndoList = new Stack<IMemento>()
	The list of memento objects that form a series of snapshots in time of a Memento_TextObject.

Detailed Description

Example of using the Memento Pattern in C#.

In this exercise, the Memento pattern is used to take snapshots of a text object so as to form an undo list of changes to the text object. Undoing an operation means restoring a snapshot of the text object.

The undo list is implemented as a stack of memento objects that each represent a snapshot of the text object taken before each operation is applied. After all operations are applied, the mementos are used to restore the text object in reverse order, effectively undoing each operation in turn.

Compare this to the Command_Exercise() and note that the steps taken there are identical to here (except for method names, of course). The difference lies in how operations are executed and undone. Mementos make the undo process much cleaner and faster since operations do not need to be applied repeatedly to get the text object into a specific state. Specifically, compare Command_Undo() with Memento_Undo(). Also note the differences in the "Memento_ApplyXXOperation()" methods, which more cleanly separate the save from the operation.

Definition at line 36 of file Memento_Exercise.cs.

Member Function Documentation

◆ Memento_ApplyReplaceOperation()

void Memento_ApplyReplaceOperation	(	Memento_TextObject	text,
		string	searchPattern,
		string	replaceText
	)

inlineprivate

Helper function to replace a pattern with another string in the given Memento_TextObject after adding a snapshot of the text object to the undo list. Finally, it shows off what was done.

Parameters

text	The Memento_TextObject to affect.
searchPattern	What to look for in the Memento_TextObject.
replaceText	What to replace the searchPattern with.

Definition at line 110 of file Memento_Exercise.cs.

References Memento_Exercise.Memento_Operation_Replace(), and Memento_Exercise.Memento_SaveForUndo().

Referenced by Memento_Exercise.Run().

◆ Memento_ApplyReverseOperation()

void Memento_ApplyReverseOperation ( Memento_TextObject text )

inlineprivate

Helper function to reverse the order of the characters in the given Memento_TextObject after adding a snapshot of the text object to an undo list. Finally, it shows what was done.

Parameters