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    <p>Ok the delegation pattern is widely used in the Cocoa framework.</p> <p>The file that parses data must have a protocol, anyone wanting callbacks form this Class must implement the methods from the protocol:</p> <pre><code> //XMLParser.h //import statements here .. @protocol XMLParserDelegate - (void) parserDidFinish:(NSArray*) theParsedData; //have as many methods as you please, didFail, doingProgress etc. @end @interface XMLParser : NSObject { id &lt;XMLParserDelegate&gt; delegate; //we don't know what type of object this will be, only that it will adhere to the XMLParserDelegate protocol. } @property(assign) id delegate; //methods @end </code></pre> <p>In the implementation of the XMLParser:</p> <pre><code>@implementation XMLParser @synthesize delegate; - (void)parserDidEndDocument:(NSXMLParser *)parser { [self.delegate parserDidFinish:dataYouCollectedArray]; //this is where it happens. } </code></pre> <p>So in your controllers interface file you says that you will adhere to the XMLParserDelegate protocol.</p> <pre><code>//MyController.h #import "XMLParser.h" @interface MyController : UIViewController &lt;XMLParserDelegate&gt; { //this is where you "promise" to implement the methods of the protocol. } </code></pre> <p>In the MyController.m file you now instantiate the XMLParser.</p> <pre><code>@implementation MyController - (void) init { XMLParser *parser = [[XMLParser alloc] init]; [parser setDelegate:self] //now the parser has a reference to this object. [parser start]; } - (void) parserDidFinish:(NSArray*) results { //now you have your results in the controller, can set it as the data source of the tableView and call tableView.reloadData; } </code></pre> <p>This is a great pattern that loosely couples the caller and responder without having them know anything other that what the protocol dictates, about each other.</p> <p>If I have a view element that is confined to its own functionality, like, say, a clock. I would have a ClockViewController and it would instantiate arm, dials, etc. They would all be linked to the clock and alert the clock controller about their actions using this pattern. This way I can use the clock arm or dial in other code as I please, as long as the object instantiating them adheres to the ClockArmDelegate protocol.</p> <p>Hope it makes sense:) it is the, Im pretty sure, most used pattern in Cocoa.</p>
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    1. COThanks for that example, made me understand how to use it fully.
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