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copied!<blockquote> <p>What does it mean when there's a sender parameter in a method header? Does it represent the instance that called it, or the method that called it?</p> </blockquote> <p>Look at the type of the argument. Chances are, it's <code>id</code>. That's the type of an object pointer. You're correct that it is the instance that sent the message.</p> <p>You can pass a <em>message selector</em> to a message, but the type for that is <code>SEL</code>, not <code>id</code>. Likewise, you can pass a <em>method implementation</em> to a message, but the type for that is <code>IMP</code>, not <code>id</code>.</p> <p>Methods that take a single <code>sender</code> argument are typically action methods, usually identified by the <code>IBAction</code> return type. As zoul said, <code>IBAction</code> expands to <code>void</code> for the compiler, which tells it that the method does not return a value. The reason to have <code>IBAction</code> is that Interface Builder looks for methods with <code>IBAction</code> as the return type and detects them as actions you can wire a control up to.</p> <p>For more information for Cocoa (Mac OS X), see <a href="http://developer.apple.com/mac/library/documentation/Cocoa/Conceptual/CocoaFundamentals/CommunicatingWithObjects/CommunicateWithObjects.html#//apple_ref/doc/uid/TP40002974-CH7-SW14" rel="nofollow noreferrer">“The Target-Action Mechanism” in the Cocoa Fundamentals Guide</a> and the <a href="http://developer.apple.com/mac/library/documentation/Cocoa/Conceptual/ControlCell/" rel="nofollow noreferrer">Control and Cell Programming Topics for Cocoa</a>.<br> For more information for Cocoa Touch (iPhone/iPod touch/iPad), see <a href="http://developer.apple.com/iphone/library/documentation/UIKit/Reference/UIControl_Class/Reference/Reference.html#//apple_ref/doc/uid/TP40006779-RH2-SW28" rel="nofollow noreferrer">“The Target-Action Mechanism” in the UIControl class reference</a>.</p>

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