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    <p><code>init...</code> methods should only be called once, immediately after a call to <code>alloc</code> or <code>allocWithZone:</code>. When framework code creates and returns an object or graph of objects, their <code>init...</code> methods have already been called, so sending another <code>init...</code> message would have undefined results. Don't do that.</p> <p>Interestingly, in spite of what the documentation appears to say (and admittedly I probably missed a key sentence or paragraph somewhere), when you create an instance of a mutable collection by reading a plist, any nested collections are also mutable. I ran the following little experiment in a test harness just to be sure:</p> <pre><code>NSMutableDictionary *pets = [NSMutableDictionary dictionaryWithContentsOfFile:@"/tmp/Pets.plist"]; NSMutableArray *cats = [pets objectForKey:@"cats"]; [cats addObject:@"Foo"]; // EDIT: Added line I accidentally omitted earlier NSLog(@"%@", cats); </code></pre> <p>So again, the nested collections created when you read in the plist are fully initialized, and mutable to boot, so you can simply use them, as you've been doing.</p> <p><strong>EDIT</strong></p> <p>However, after doing some further reading of the docs, I think the OP is right to feel uneasy about relying on what is apparently an undocumented feature of the current version of the SDK. For example, the <em>Property List Programming Guide</em> states:</p> <blockquote> <p>If you load the property list with this call:</p> <pre><code>NSMutableArray * ma = [NSMutableArray arrayWithContentsOfFile:xmlFile]; </code></pre> <p><code>ma</code> is a mutable array with immutable dictionaries in each element. Each key and each value in each dictionary are immutable.</p> </blockquote> <p>So, to be on the safe side, if you need a nested collection to be mutable, you should create it yourself. For example, I'd recommend rewriting the code in the example above as follows:</p> <pre><code>NSMutableDictionary *pets = [NSMutableDictionary dictionaryWithContentsOfFile:@"/tmp/Pets.plist"]; NSArray *cats = [pets objectForKey:@"cats"]; NSMutableArray *mutableCats = [cats mutableCopy]; [pets setObject:mutableCats forKey:cats]; [mutableCats release]; </code></pre> <p>You can then safely make changes to the nested mutable collection:</p> <pre><code>[mutableCats addObject:@"Foo"]; </code></pre>
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    1. PODo I need to initialize an iOS empty nested array that's part of a plist import?
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    1. COCould you explain the significance of your "experiment" code? I don't understand how this would confirm that nested collections are initialized and mutable and ready to go (unless there was pertinent content in your plist that you just haven't shared). Thanks!
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    2. COWhoops, accidentally deleted a line, I'll edit my answer.
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    3. COWell, I know I can create a nested collection manually, but that seems rather inefficient (or extremely inefficient) for complex data structures. Surely there's a way to use a plist to create a dictionary with mutable sub-dictionaries? Some sort of processing you can do on it once it's imported?
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