1 @property (retain, nonatomic) NSString *retainStr;  2 @property (copy, nonatomic)   NSString *copyStr;  3   4    5   6 @property (retain, nonatomic) NSMutableString *retainMStr;  7 @property (copy, nonatomic)   NSMutableString *copyMStr;  8   9   10  11 实现代码如下： 12  13     NSMutableString *mStr = [NSMutableString string]; 14  15     [mStr setString:@"我没变"]; 16  17      18  19     self.retainStr   = mStr; 20  21     self.copyStr     = mStr; 22  23     self.retainMStr = mStr; 24  25     self.copyMStr   = mStr; 26  27      28  29     NSLog(@"retainStr:%@",  self.retainStr); 30  31     NSLog(@"copyStr:%@",    self.copyStr); 32  33     NSLog(@"retainMStr:%@", self.retainMStr); 34  35     NSLog(@"copyMStr:%@",   self.copyMStr); 36  37     NSLog(@"\n"); 38  39      40  41     [mStr setString:@"我变了"]; 42  43      44  45     NSLog(@"retainStr:%@",  self.retainStr); 46  47     NSLog(@"copyStr:%@",    self.copyStr); 48  49     NSLog(@"retainMStr:%@", self.retainMStr); 50  51     NSLog(@"copyMStr:%@",   self.copyMStr); 52  53     NSLog(@"\n"); 54  55   56  57     NSString *str = @"我来了";//[[NSString alloc] initWithFormat:@"我来了"];//两种方式都一样。 58  59     self.retainStr  = str; 60  61     self.copyStr    = str; 62  63     self.retainMStr = [str mutableCopy]; 64  65     self.copyMStr   = [str mutableCopy]; 66  67   68  69     NSLog(@"retainStr:%@",  self.retainStr); 70  71     NSLog(@"copyStr:%@",    self.copyStr); 72  73     NSLog(@"retainMStr:%@", self.retainMStr); 74  75     NSLog(@"copyMStr:%@",   self.copyMStr); 76  77     NSLog(@"\n"); 78  79      80  81     str =@"我走了";//[[NSStringalloc] initWithFormat:@"我走了"];//两种方式都一样 82  83   84  85     NSLog(@"retainStr:%@",  self.retainStr); 86  87     NSLog(@"copyStr:%@",    self.copyStr); 88  89     NSLog(@"retainMStr:%@", self.retainMStr); 90  91     NSLog(@"copyMStr:%@",   self.copyMStr); 92  93     NSLog(@"\n"); 94  95   96  97 打印结果如下： 98  99 2012-10-12 13:53:14.858 StringDemo[1515:11303] retainStr:我没变100 101 2012-10-12 13:53:14.860 StringDemo[1515:11303] copyStr:我没变102 103 2012-10-12 13:53:14.861 StringDemo[1515:11303] retainMStr:我没变104 105 2012-10-12 13:53:14.862 StringDemo[1515:11303] copyMStr:我没变106 107 2012-10-12 13:53:14.863 StringDemo[1515:11303] 108 109 2012-10-12 13:53:14.864 StringDemo[1515:11303] retainStr:我变了110 111 2012-10-12 13:53:14.865 StringDemo[1515:11303] copyStr:我没变112 113 2012-10-12 13:53:14.866 StringDemo[1515:11303] retainMStr:我变了114 115 2012-10-12 13:53:14.867 StringDemo[1515:11303] copyMStr:我没变116 117 2012-10-12 13:53:14.868 StringDemo[1515:11303] 118 119 2012-10-12 13:53:14.869 StringDemo[1515:11303] retainStr:我来了120 121 2012-10-12 13:53:14.869 StringDemo[1515:11303] copyStr:我来了122 123 2012-10-12 13:53:14.870 StringDemo[1515:11303] retainMStr:我来了124 125 2012-10-12 13:53:14.871 StringDemo[1515:11303] copyMStr:我来了126 127 2012-10-12 13:53:14.872 StringDemo[1515:11303] 128 129 2012-10-12 13:53:14.873 StringDemo[1515:11303] retainStr:我来了130 131 2012-10-12 13:53:14.874 StringDemo[1515:11303] copyStr:我来了132 133 2012-10-12 13:53:14.875 StringDemo[1515:11303] retainMStr:我来了134 135 2012-10-12 13:53:14.876 StringDemo[1515:11303] copyMStr:我来了