Strong和Copy對于NSString秘血、NSDirectory、NSArray的區(qū)別
當(dāng)NSString、NSDirectory咒精、NSArray在聲明屬性的時候設(shè)置為Strong類型時:
(1) 調(diào)用set方法賦值
@property (nonatomic, strong) NSString *str;
@property (nonatomic, strong) NSArray *array;
@property (nonatomic, strong) NSDictionary *dic;
NSMutableString *mustr = [[NSMutableString alloc]initWithFormat:@"123"];
self.str = mustr;
NSLog(@"%@",_str);
[mustr appendString:@"456"];
NSLog(@"%@",_str);
NSMutableArray *muarray = [NSMutableArray arrayWithObjects:@"a",@"b",@"c",nil];
self.array = muarray;
NSLog(@"%@",_array);
[muarray addObject:@"d"];
NSLog(@"%@",_array);
NSMutableDictionary *muDic = [NSMutableDictionary dictionaryWithObjectsAndKeys:@"a",@"1",@"b",@"2",nil];
self.dic = muDic;
NSLog(@"%@",_dic);
[muDic setObject:@"3" forKey:@"c"];
NSLog(@"%@",_dic);
輸出結(jié)果：
屏幕快照 2017-02-23 17.40.33.png
（2）直接對實(shí)例對象賦值
@property (nonatomic, strong) NSString *str;
@property (nonatomic, strong) NSArray *array;
@property (nonatomic, strong) NSDictionary *dic;
NSMutableString *mustr = [[NSMutableString alloc]initWithFormat:@"123"];
_str = mustr;
NSLog(@"%@",_str);
[mustr appendString:@"456"];
NSLog(@"%@",_str);
NSMutableArray *muarray = [NSMutableArray arrayWithObjects:@"a",@"b",@"c",nil];
_array = muarray;
NSLog(@"%@",_array);
[muarray addObject:@"d"];
NSLog(@"%@",_array);
NSMutableDictionary *muDic = [NSMutableDictionary dictionaryWithObjectsAndKeys:@"a",@"1",@"b",@"2",nil];
_dic = muDic;
NSLog(@"%@",_dic);
[muDic setObject:@"3" forKey:@"c"];
NSLog(@"%@",_dic);
輸出結(jié)果：
屏幕快照 2017-02-23 17.47.13.png
結(jié)論：當(dāng)把NSString密末、NSDirectory握爷、NSArray聲明為strong，那么如果原對象的值發(fā)生變化严里，會影響到當(dāng)前對象的值,不管當(dāng)前對象是調(diào)用點(diǎn)語法賦值還是直接對實(shí)例對象賦值新啼。
當(dāng)NSString、NSDirectory刹碾、NSArray在聲明屬性的時候設(shè)置為Copy類型時:
(1)調(diào)用set方法賦值
@property (nonatomic, copy) NSString *str;
@property (nonatomic, copy) NSArray *array;
@property (nonatomic, copy) NSDictionary *dic;
self.str = mustr;
NSLog(@"%@",_str);
[mustr appendString:@"456"];
NSLog(@"%@",_str);
NSMutableArray *muarray = [NSMutableArray arrayWithObjects:@"a",@"b",@"c",nil];
self.array = muarray;
NSLog(@"%@",_array);
[muarray addObject:@"d"];
NSLog(@"%@",_array);
NSMutableDictionary *muDic = [NSMutableDictionary dictionaryWithObjectsAndKeys:@"a",@"1",@"b",@"2",nil];
self.dic = muDic;
NSLog(@"%@",_dic);
[muDic setObject:@"3" forKey:@"c"];
NSLog(@"%@",_dic);
輸出結(jié)果：
屏幕快照 2017-02-23 18.08.58.png
（2）直接對實(shí)例對象賦值
@property (nonatomic, copy) NSString *str;
@property (nonatomic, copy) NSArray *array;
@property (nonatomic, copy) NSDictionary *dic;
NSMutableString *mustr = [[NSMutableString alloc]initWithFormat:@"123"];
_str = mustr;
NSLog(@"%@",_str);
[mustr appendString:@"456"];
NSLog(@"%@",_str);
NSMutableArray *muarray = [NSMutableArray arrayWithObjects:@"a",@"b",@"c",nil];
_array = muarray;
NSLog(@"%@",_array);
[muarray addObject:@"d"];
NSLog(@"%@",_array);
NSMutableDictionary *muDic = [NSMutableDictionary dictionaryWithObjectsAndKeys:@"a",@"1",@"b",@"2",nil];
_dic = muDic;
NSLog(@"%@",_dic);
[muDic setObject:@"3" forKey:@"c"];
NSLog(@"%@",_dic);
當(dāng)設(shè)置為Copy屬性時燥撞，如果調(diào)用點(diǎn)語法賦值，當(dāng)前對象不會因?yàn)樵瓕ο蟮母淖兌淖兠灾模侨绻侵苯淤x值物舒，那么原對象改變那么當(dāng)前對象也會改變。
總結(jié)：當(dāng)對NSString這種有可變子類的對象直接賦值時戏锹，不管聲明屬性時聲明的是copy還是strong,現(xiàn)對象的值都會隨著原對象的值而改變冠胯。當(dāng)調(diào)用set方法賦值時，如果對象聲明的是copy那么現(xiàn)有對象不會因?yàn)樵瓕ο蟮母淖兌淖兙坝茫绻暶鞯氖莝trong涵叮，那么現(xiàn)有對象會因?yàn)樵瓕ο蟮母淖兌淖儭?/p>
個人理解：聲明為strong時，其實(shí)只是把當(dāng)前對象的指針指向了原有對象的地址伞插，因此當(dāng)原有對象改變時割粮，現(xiàn)有對象也會改變。直接賦值也應(yīng)該是這樣媚污。當(dāng)聲明為Copy時舀瓢，其實(shí)是把原有對象復(fù)制了一份，然后讓現(xiàn)有對象的指針指向復(fù)制的這一份耗美。
