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POid type instance variable sending messages to instance methods
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  1. POid type instance variable sending messages to instance methods
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    copied!<p>my first question on stackoverflow so please be gentle. I've tried searching for answers but I really need help with this.</p> <p>The issue is with learning about delegates from Neal Goldstein's Objective-C for Dummies</p> <p>He has the following in <strong>Transaction.h</strong></p> <pre><code>#import &lt;Cocoa/Cocoa.h&gt; @class Budget; @interface Transaction : NSObject { Budget *budget; double amount; NSString *name; id delegate; } //some init method @end @protocol TransactionDelegate @required - (void) spend: (Transaction *) aTransaction; //additional optional method @end -- </code></pre> <p>//and then in <strong>Transaction.m</strong> he has this</p> <pre><code>#import "Transaction.h" #import "Budget.h" @implementation Transaction @synthesize budget, delegate , amount; - (void) spend { if ([delegate respondsToSelector:@selector(spend:)]) [delegate spend:self]; } - (id) initWithAmount: (double) theAmount forBudget: (Budget*) aBudget { if (self = [super init]) { budget = aBudget; [budget retain]; amount = theAmount; } return self; } - (void) dealloc { [budget release]; [super dealloc]; } @end </code></pre> <p>I have problem understanding the spend method in the Transaction.m file</p> <p>Can the id type instance variable call ANY method in the class that contains it? I understand that respondsToSelector is a NSObject method that tells the compiler if a method has been implemented. But how can delegate which is of id-type call that method? the compiler does not even know what object it is yet...</p> <p>Please help!</p> <p>P.S. if anybody has any recommendations on good Objective-C books, I'd highly appreciate it. I wanna get into iPhone development but I figured I need to get a good grasp on the basics of Objective-C first.</p> <p>Thanks!</p>
 

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