iOS nsstring type why copy decoration

In the process of development, only know the NSString type is best to use copy decoration and can not use strong, but do not know why, today understand the next, finally understand.

As shown below, when the modifier is copy, because Nsmutablestring is a subclass of the NSString type, So you can use pointer self.name to point to MSTR, but we know that the meaning of copy refers to the deep copy of the new object when the value is re-assigned to Self.name.

So at this point self.name pointer and MSTR pointer to the object is different, so when the Mstr object to send the method appendstring, the change is only MSTR (this time the value becomes mutablestring----addstring), and Self.name still does not Change (mutablestring----), whereas the modifier is strong, because strong means that the pointer points to the original object, and the reference count + 1, so self.name and Mstr point to the same object, and self.name changes together when MSTR is modified. Therefore, in order to avoid the value of the NSString type being modified, it is generally recommended to modify it with the copy modifier.

@interface*name; // @property (Nonatomic,strong) nsstring *name; @end

- (void) viewdidload {[Super viewdidload]; Nsmutablestring*MSTR = [Nsmutablestring stringWithFormat:@"mutablestring----"]; Self.name=MSTR; [MSTR appendString:@"addstriing"];//when the modifier for name is copy, the result of name is mutablestring----NSLog (@"%@", MSTR);//when the modifier for name is strong, the result of name is mutablestring----addstriingNSLog (@"%@", Self.name);}

iOS nsstring type why copy decoration