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POQuestion about pointers in Objective-C
 

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  1. POQuestion about pointers in Objective-C
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    <p>In a <code>global.h</code> file I declare</p> <pre><code>dataManager *IdataManager; </code></pre> <p>Then later when the program initializes I allocate and initialize the variable, and use it in several different views as a means of accessing a set of data that gets downloaded when the app starts up.</p> <p>Recently I noticed when I pull up one of my views, close it, and then open it again, I get a crash when trying to access the global <code>IdataManager</code>.</p> <p>I finally came to the conclusion that it's contents were being released somehow by the view being de-initialized. I looked at the only place I was using the variable:</p> <pre><code>CCandidate *currentCandidate = [IdataManager CurrentCandidate]; </code></pre> <p>So I changed this to say:</p> <pre><code>CCandidate *currentCandidate = [[IdataManager CurrentCandidate] retain]; </code></pre> <p>I wasn't sure how the retain keyword worked, but it sounded like if the view really was releasing my data, I should specify in the creation of this pointer that it should be retained.</p> <p>This fixed the crashing, but I don't really understand why this happened. Does objective-c just always release pointers you created when you dealloc it's owner? I was under the impression I was simply storing a memory address and giving it the name currentCandidate.</p> <p>CCandidate.h:</p> <pre><code>#import &lt;Foundation/Foundation.h&gt; @interface CCandidate : NSObject { int ID; NSString* FName; NSString* MName; NSString* LName; NSString* FullName; NSString* DOB; NSString* Occupation; NSString* Employer; NSString* Phone; NSString* Fax; NSString* Email; NSString* Website; NSString* Party; NSString* TwitterUName; NSString* TwitterHashTag; NSString* Biography; NSString* BiographyLink; NSString* co; NSString* cb; NSString* uo; NSString* ub; } - (id) init; @property (nonatomic, assign) int ID; @property (nonatomic, retain) NSString* FName; @property (nonatomic, retain) NSString* MName; @property (nonatomic, retain) NSString* LName; @property (nonatomic, retain) NSString* FullName; @property (nonatomic, retain) NSString* DOB; @property (nonatomic, retain) NSString* Occupation; @property (nonatomic, retain) NSString* Employer; @property (nonatomic, retain) NSString* Phone; @property (nonatomic, retain) NSString* Fax; @property (nonatomic, retain) NSString* Email; @property (nonatomic, retain) NSString* Website; @property (nonatomic, retain) NSString* Party; @property (nonatomic, retain) NSString* TwitterUName; @property (nonatomic, retain) NSString* TwitterHashTag; @property (nonatomic, retain) NSString* Biography; @property (nonatomic, retain) NSString* BiographyLink; @property (nonatomic, retain) NSString* co; @property (nonatomic, retain) NSString* cb; @property (nonatomic, retain) NSString* uo; @property (nonatomic, retain) NSString* ub; @end </code></pre> <p>CCandidate.m:</p> <pre><code>#import "CCandidate.h" @implementation CCandidate @synthesize ID; @synthesize FName; @synthesize MName; @synthesize LName; @synthesize FullName; @synthesize DOB; @synthesize Occupation; @synthesize Employer; @synthesize Phone; @synthesize Fax; @synthesize Email; @synthesize Website; @synthesize Party; @synthesize TwitterUName; @synthesize TwitterHashTag; @synthesize Biography; @synthesize BiographyLink; @synthesize co; @synthesize cb; @synthesize uo; @synthesize ub; -(id) init { self = [super init]; ID = -1; return self; } @end </code></pre>
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    1. COLearn how to write a correct init-method: http://www.mikeash.com/?page=pyblog/the-how-and-why-of-cocoa-initializers.html
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    2. COHow are you initializing the global variable? I think it could be that this variable is autoreleased.
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    3. COAfter a connectionDidFinishLoading callback I set: IdataManager = [[dataManager alloc] initWithData:receivedData];
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