问题
If I have a dictionary with the following key/value "foo"/"bar" and declared [dictionary setObject:@"baz" forKey:@"foo"]; would this replace the current key value pair with "foo"/"baz" and delete "foo"/"bar"?
回答1:
The behave of an NSMutableDictionary (as any common hash table) is that if it does not exists it creates a new key/value pair, if it already exits it will replace the existing value with the new one.
回答2:
The documentation here;
http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/NSMutableDictionary_Class/Reference/Reference.html%23//apple_ref/doc/uid/TP40003692
suggests that it would. But please, don't take my word for it, read them yourself.
Perhaps you should also read;
http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/Collections/Collections.html%23//apple_ref/doc/uid/10000034i
来源：https://stackoverflow.com/questions/5736605/replacing-key-value-in-nsdictionary