为什么@ 1的保留计数等于7、8或10? [英] Why is the retain count of @1 equal to 7, 8 or 10?

问题描述

我在Xcode 4.4.1上创建了一个空的iOS应用，并执行了以下操作:

I created an empty iOS app on Xcode 4.4.1, and did the following:

NSNumber *n1 = @1;
NSNumber *n2 = @2;
NSNumber *n3 = @3;
NSNumber *n100 = @100;

NSString *s = @"haha";
NSArray *a = @[n1, s];
NSDictionary *d = @{ @"ha" : @1, @3 : @"hello" };

NSLog(@"retain count of @1 is %i", [n1 retainCount]);
NSLog(@"retain count of @2 is %i", [n2 retainCount]);
NSLog(@"retain count of @3 is %i", [n3 retainCount]);
NSLog(@"retain count of @100 is %i", [n100 retainCount]);

NSLog(@"retain count of @\"haha\" is %i", [s retainCount]);

NSLog(@"retain count of array literal is %i", [a retainCount]);
NSLog(@"retain count of dictionary literal is %i", [d retainCount]);

结果是:

retain count of @1 is 10
retain count of @2 is 4
retain count of @3 is 5
retain count of @100 is 1
retain count of @"haha" is -1
retain count of array literal is 1
retain count of dictionary literal is 1

因此，数组文字和字典文字的保留计数为1，并且字符串字面量在整个应用程序的运行中都存在，因此这就是为什么它为-1(可能表示MAX unsigned int)，但保留计数为@1实际上在不同时间显示为7、8和10.有规则吗?我发现我也可以执行[n1 retain]和[n1 release]，它会相应增加和减少保留计数.

so the retain count of array literal and dictionary literal is 1, and string literal is said to exist for the whole app's running, so that's why it is -1 (probably meaning MAX unsigned int), but the retain count of @1 actually come out as 7, 8, and 10 at different times. Is there a rule to it? I found that I can do [n1 retain] and [n1 release] as well, and it will increase and decrease the retain count accordingly.

推荐答案

我认为这表明了原因:每次遇到@1时，它都类似于[[[NSNumber alloc] initWithInt:1] autorelease]，并且看起来返回的是相同的目的.因此，当完成以下操作时:

I think this points to the reason why: every time @1 is encountered, it is something like [[[NSNumber alloc] initWithInt:1] autorelease], and it appears that it returns the same object. So when the following is done:

NSMutableArray *arr = [[NSMutableArray alloc] init];
for (int i = 0; i < 300; i++) {
    [arr addObject:@1];
}

保留数实际上变为610.如果执行以下操作，则保持不变:

the retain count actually becomes 610. And it is the same if the following is done:

NSMutableArray *arr = [[NSMutableArray alloc] init];
for (int i = 0; i < 300; i++) {
    [arr addObject:[[[NSNumber alloc] initWithInt:1] autorelease]];
} 

(更新:为610，因为使用@1将保留计数增加1，并且将其保留在数组中的另一个时间，因此总计为600倍).这表明在任何地方使用@1都会增加保留计数，并且此NSNumber对象可能会以相同的次数放置在自动释放池中.

(Update: it is 610, because the retain count is increased by 1 by the usage of @1, and another time when it is retained by the array, so it is 600 times total). It suggests that any usage of @1 any where will increase the retain count, and this NSNumber object is probably placed in the autorelease pool the same equal number of times.

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