13 lines
960 B
Plaintext
13 lines
960 B
Plaintext
A delegate is a helper object used by another object. The delegator may send the delegate certain messages, and provide a default implementation when there is no delegate or the delegate does not respond to a message. This pattern is heavily used in [http://developer.apple.com/documentation/Cocoa/Conceptual/CocoaFundamentals/CocoaDesignPatterns/chapter_5_section_3.html#//apple_ref/doc/uid/TP40002974-CH6-DontLinkElementID_93 Cocoa framework on Mac OS X]. See also [[wp:Delegation pattern]].
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Objects responsibilities:
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Delegator:
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* Keep an optional delegate instance.
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* Implement "operation" method, returning the delegate "thing" if the delegate respond to "thing", or the string "default implementation".
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Delegate:
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* Implement "thing" and return the string "delegate implementation"
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Show how objects are created and used. First, without a delegate, then with a delegate that does not implement "thing", and last with a delegate that implements "thing".
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