Question

我有几个关于ARC（自动引用计数）的问题：

CFURLRef url = (__bridge CFURLRef)[NSURL fileURLWithPath:appPath];
//Question 1: Here, I would expect the NSURL object to be autoreleased and
//therefore the CFURLRef will also be available for “a while.” Is this correct?

url = NULL;
//Question 2: Will this cause the NSURL to be released immediately?

NSURL *url = [NSURL fileURLWithPath:appPath];
url = nil;
//Question 3: Does the “url = nil” result in an immediate release of the NSURL?

NSURL *url = [[NSURL alloc] initWithString:@"/something"];
url = nil;
//Question 4: What about this?

Answer 1

CFURLRef url = (__bridge CFURLRef)[NSURL fileURLWithPath:appPath];
//Question 1: Here, I would expect the NSURL object to be autoreleased and
//therefore the CFURLRef will also be available for “a while.” Is this correct?

是的，因为它们是同一个对象。只有类型改变;它仍然是对同一个对象的相同引用。

那就是说，在你释放你的最后一个所有权之后，期望一个对象继续“可用'一段时间'”是脆弱的。如果您打算继续使用该对象，请至少拥有该对象。当你完成它之后立即释放它。

url = NULL;
//Question 2: Will this cause the NSURL to be released immediately?

NSURL *url = [NSURL fileURLWithPath:appPath];
url = nil;
//Question 3: Does the “url = nil” result in an immediate release of the NSURL?

是和否。

对强变量的赋值（除非另有说明，否则变量隐式强）会立即释放先前的值并保留新值。 NSURL对象的每个赋值都会导致保留对象; nil的每个分配都导致先前持有的对象被释放。

但是，在这两种情况下，URL对象可能已由fileURLWithPath:自动释放。与往常一样，自动释放是在自动释放池结束之前到期的，因此对象可能会继续存在直到那时。这通常不是问题，但如果您制作了大量对象（例如，在紧密循环中），它偶尔会弹出。

就您而言，是的，nil的每项任务都会释放之前居住的对象，履行并终止您对该所有权的责任。

NSURL *url = [[NSURL alloc] initWithString:@"/something"];
url = nil;
//Question 4: What about this?

相同：您的作业释放了对象。由于这个中没有自动释放（你自己alloc），物体会立即死亡。

这些对象何时在ARC下发布？

1 个答案: