I think the question is clear enough but still - what's the difference between:
NSString *string = @"Hello world!"; and
NSString *string = [[NSString alloc] initWithString:@"Hello world!"]; Let me know if this already answers it.
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问题:
回答1:
NSString *string = [[NSString alloc] initWithString:@"Hello world!"]; Per cocoa as cocoa naming convention, You create an object using a method whose name begins with “alloc”, “new”, “copy”, or “mutableCopy”. That means you own the string above, hence you're responsible to release the object.
NSString *string = @"Hello World"; The line above is a string literal / constant, you don't alloc it or release it. You don't own this object.
回答2:
NSString *string = [[NSString alloc] initWithString:@"Hello World!"]; This code creates a strong reference and the variable will be retained. It then assigns the value "Hello World!" to it.
NSString *string = @"Hello World!"; This code simply assigns the value "Hello World!" to the NSString object. It's not creating any references of any kind. If your object isn't already initialized and retained, the object will be destroyed at the end of the running scope.