提示 : ?為了方便查看引用計數(shù), ARC環(huán)境修改為MRC, 步驟如下

選擇項目 Target -> Build Sttings -> All -> 搜索‘a(chǎn)utomatic’ -> 把 Objective-C Automatic Reference Counting 設(shè)置為 NO岩齿，如下圖：

arc-->mrc

類型 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ????????????????????????????????????? ?初始化后的retainCount

__NSCFConstantString (retain/release不起作用,系統(tǒng)進(jìn)行維護(hù),程序中內(nèi)容相同的常量字符串只有一個) ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? -1

__NSCFString?(retain/release有作用)? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ????? ? ? ? 1

__NSTaggedPointerString?(retain/release不起作用)? ? ? ? ? ? ? ? ? ? ? ? ?-1

__NSCFConstantString類型如下:

NSString *str = @"test";?//__NSCFConstantString

NSLog(@"%d",[str retainCount]); ?// -1

NSString *str = [NSString stringWithString:@"test"];?//__NSCFConstantString

NSLog(@"%d",[str retainCount]); ?// -1

__NSTaggedPointerString類型如下:

NSString *str = [NSString stringWithFormat:@"%s","test"];//__NSTaggedPointerString

NSLog(@"%d",[str retainCount]); ? // -1

?NSString *a = @"a"; NSString *b = [[a mutableCopy] copy];//__NSTaggedPointerString

NSLog(@"%d",[b retainCount]); // -1

__NSCFString類型如下 :

通過stringWithFormat構(gòu)造

?NSString *str = [NSString stringWithFormat:@"%s,%@","test",@"test"];//__NSCFString

? NSLog(@"%d",[str retainCount]); // 1

stringWithString + stringWithFormat構(gòu)造

NSString *str = [NSString stringWithString:[NSString stringWithFormat:@"test"]];//__NSCFString

NSLog(@"%d",[str retainCount]); // 1

NSString *str = [NSString stringWithString:[NSString stringWithFormat:@"%s","test"]];//__NSCFString

NSLog(@"%d",[str retainCount]); //1

NSString *str = [NSString stringWithString:[NSString stringWithFormat:@"%s,%d","test",10]];//__NSCFString

NSLog(@"%d",[str retainCount]); // 1

stringWithString+__NSTaggedPointerString(類型) 構(gòu)造

? ? NSString *str = [NSString stringWithFormat:@"%s", "str2"];//__NSTaggedPointerString

? ? NSString *str1 = [NSString stringWithString:[NSString stringWithFormat:@"%s", "str2"]];

? ? NSLog(@"%d",[str1 retainCount]); //1

stringWithString+__NSCFString(類型) 構(gòu)造

? ? NSString *str = [NSString stringWithFormat:@"%s,%d", "test",10];//__NSCFString

? ? NSString *str1 = [NSString stringWithString:str];

? ? NSLog(@"%d",[str1 retainCount]); //2

NSMutableString(對象)構(gòu)造

? NSMutableString* str = [NSMutableString stringWithString:@"test"];//__NSCFString

? NSLog(@"%d",[str retainCount]); //1