IOS保留,分配

Question

我观察到以下行为.

取了两个属性变量.

@property (nonatomic, retain) NSString *stringOne;
@property (nonatomic, assign) NSString *stringTwo;

在.m文件中写下代码..

 NSMutableString *localstring= [[NSMutableString alloc] initWithString:@"test"];
 self.stringOne = localstring;
 NSLog(@"localstring = %d", [string retainCount]);
 NSLog(@"string one retain count = %d", [self.stringOne retainCount]);
 self.stringTwo = localstring;
 NSLog(@"localstring = %d", [localstring retainCount]);
 NSLog(@"string two  retain count = %d", [self.stringTwo retainCount]);

由于alloc,localstring保留计数为1.现在我给了self.stringOne = localString.

由于stringOne的retain属性,localstring的保留计数将变为2.现在我给了self.stringTwo = localString.

即使在这里,localstring保留计数也会增加1.请注意,我已将assign属性赋予stringTwo.实际上,localstring或stringTwo的保留计数不应该增加1,因为它是assign属性.如果我错了,请纠正我.

谢谢Jithen

Answer 1

倾倒retainCount; 它没用. http://www.whentouseretaincount.com/

您混淆的根源在于不了解指针的工作原理.像这样修改你的代码:

@interface BBQ:NSObject
@property (nonatomic, retain) NSString *stringOne;
@property (nonatomic, assign) NSString *stringTwo;
@end

@implementation BBQ
- (void) burn
{
    NSMutableString *localstring= [[NSMutableString alloc] initWithString:@"test"];
    self.stringOne = localstring;
    NSLog(@"localstring = %p", localstring);
    NSLog(@"string one = %p", self.stringOne);
    self.stringTwo = localstring;
    NSLog(@"localstring = %p", localstring);
    NSLog(@"string two  = %p", self.stringTwo);
}
@end

它会喷出这样的东西:

2013-04-11 08:48:13.770 asdffadsfasddfsa[18096:303] localstring = 0x10010aaf0
2013-04-11 08:48:13.772 asdffadsfasddfsa[18096:303] string one = 0x10010aaf0
2013-04-11 08:48:13.772 asdffadsfasddfsa[18096:303] localstring = 0x10010aaf0
2013-04-11 08:48:13.772 asdffadsfasddfsa[18096:303] string two  = 0x10010aaf0

只有一个字符串实例在播放; localstring,stringOne和stringTwo所有人都只引用了一个NSMUtableString实例.

因此,你会看到+1 RC 是一个字符串实例为alloc,一为分配到stringOne属性和没有变化stringTwo.

(RC只应该根据增量进行推理;如果保留一个对象,则需要在不再需要该对象时将其与一个版本进行平衡.该对象可能被其他东西保留是无关紧要的.)