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POProper, memory-managed implementation of custom NSDictionary getter
 

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  1. POProper, memory-managed implementation of custom NSDictionary getter
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    <p>Thanks in advance...</p> <p>So after some recent memory leaks and bugs (documented <a href="https://stackoverflow.com/questions/7623989/plugging-a-sortedarrayusingselector-and-or-initwitharray-memory-leak-between-clas" title="here">here</a>), I've been studying up on my memory management, and I am now trying to write a custom getter for an NSDictionary in a helper class I have.</p> <p>The reasons for the custom getter are:</p> <p>First, it's a calculated dictionary, so for performance issues I want to return the cached object unless it's necessary to regenerate it (my example below isn't too computationally expensive, but others in the class will be).</p> <p>Second, I want to lazily instantiate. I only want to generate the dictionary if another class "asks" for it, which is why I'm checking for nil in the getter.</p> <p>So, the questions. The code below represents my first ever (studied) attempt at writing custom setter/getter, I usually just synthesize.</p> <p>1) Is this proper implementation and proper memory management?</p> <p>2) Is this best?</p> <p>3) Is the BOOL <code>installedStandardsChangedSinceLastRead</code> the best way to flag the need to recalculate? This would happen if other methods in the class had changed something. But should I just have those methods nil out <code>_installedStandards</code> instead, since that would also trigger the recalculate?</p> <p>4) Finally, if I <strong>did</strong> just have the other methods nil out the iVar to flag it for recalculation, how would I make sure I don't leak? Would I use the setter (i.e. <code>self.installedStandards = nil</code>), nil the iVar directly (i.e. <code>_installedStandards = nil</code>), or something else?</p> <p>(Oh, and if I nil'd the iVar directly, would I need to release it first? It seems like correct would be <code>[_installedStandards release]; _installedStandards = nil</code>? In which case couldn't I just use <code>self.installedStandards = nil</code>?)</p> <p><strong>Onto the code!</strong> <em>Reminder that this is a simplified version of what will be a more complex class (see link at top) with lots of these setters/getters. I need to make sure I'm executing properly before I flesh it out.</em></p> <p><strong>.h file</strong></p> <pre><code>@interface InstalledStandardTracker20 : NSObject { NSDictionary *_installedStandards; BOOL _installedStandardsChangedSinceLastRead; } @property (nonatomic, retain) NSDictionary *installedStandards; @property (nonatomic) BOOL installedStandardsChangedSinceLastRead; @end </code></pre> <p><strong>@implementation</strong></p> <pre><code>@implementation InstalledStandardTracker20 @synthesize installedStandardsChangedSinceLastRead = _installedStandardsChangedSinceLastRead; - (void)refreshInstalledStandards { NSUserDefaults *currentDefaults = [NSUserDefaults standardUserDefaults]; self.installedStandards = [currentDefaults objectForKey:@"installedStandards"]; self.installedStandardsChangedSinceLastRead = NO; } - (NSDictionary *)installedStandards { if (!_installedStandards || self.installedStandardsChangedSinceLastRead) { [self refreshInstalledStandards]; } return _installedStandards; } - (void)setInstalledStandards:(NSDictionary *)newInstalledStandards { [newInstalledStandards retain]; [_installedStandards release]; _installedStandards = newInstalledStandards; } </code></pre>
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