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Generating Your Own ErrorsIn order to create your own NSError objects you’ll need to define your own error domain, which should be of the form:com.com... 阅读全文
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Blocks make this much easier, however, because you can define the callback behavior at the time you initiate the task, like this:- (IBAction)fetchRemo... 阅读全文
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Represent nil with NSNullIt’s not possible to add nil to the collection classes described in this section because nil in Objective-C means “no object.... 阅读全文