-copy, as implemented by mutable Cocoa classes, always returns their immutable counterparts. Thus, when an NSMutableArray is sent -copy, it returns an NSArray containing the same objects.
实测：
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@property(nonatomic,copy)NSMutableArray
*arrayCopy;@property(nonatomic,strong)NSMutableArray
*arrayStrong;self.arrayCopy=[[NSMutableArrayalloc]init];self.arrayStrong=[NSMutableArrayarrayWithArray:@[@"strong1",@"strong2"]];[self.arrayCopy addObject:@"copy1"];[self.arrayStrong addObject:@"strong3"]; |
报错：
-[__NSArrayI addObject:]: unrecognized selector sent to instance 0x100107090
而arrayStrong则不会错
给NSMutableArray添加copy属性就变成了NSArray,布布扣,bubuko.com
给NSMutableArray添加copy属性就变成了NSArray
原文：http://www.cnblogs.com/walkerwang/p/3571865.html