objective-c - 这些对象什么时候在 ARC 下被释放？

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；它仍然是对同一对象的相同引用。

也就是说，期望一个对象在您释放它的最后所有权后继续“可用‘一段时间’”是很脆弱的。如果您打算继续使用该对象，请至少拥有它那么久。完成后立即释放它。

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?

是也不是。

对强变量的赋值(除非另有说明，否则变量隐含地是强变量)会立即释放先前的值并保留新值。 NSURL 对象的每次赋值都会导致该对象被保留； nil 的每次赋值都会导致先前持有的对象被释放。

然而，在这两种情况下，URL 对象可能已被 fileURLWithPath: 自动释放。与往常一样，该自动释放不会早于自动释放池结束时到期，因此该对象可能会一直存在到那时。这通常不是问题，但如果您正在制作大量对象(例如，在紧密循环中)，它偶尔会弹出。

就您而言，是的，每次分配 nil 都会释放之前驻留在那里的对象，从而履行并结束您对该所有权的责任。

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

此处相同:您的分配释放对象。由于这个对象没有自动释放(您自己分配)，该对象将立即消亡。