Objective-C 保留澄清

Question

我正在查看这段代码：

NSMutableArray *controllers = [[NSMutableArray alloc] init];
for (unsigned i = 0; i < kNumberOfPages; i++) {
    [controllers addObject:[NSNull null]];
}
self.viewControllers = controllers;
[controllers release];

稍后...

- (void)dealloc {
    [viewControllers release];
    ...
}

我看到 self.viewControllers 和控制器现在指向相同的分配内存（类型为 NSMutableArray *），但是当我调用 [controllers release] 时，self.viewControllers 并未被释放以及，或者设置 self.viewControllers = controllers 自动保留该内存？

Answer 1

点符号 (self.foo = bar;) 相当于调用 [self setFoo:bar];。如果您的属性被声明为保留其值，那么您的视图控制器将在这种情况下保留该数组，并在您设置新值后释放它。

Answer 2

我假设 viewControllers 是一个保留关联值的属性。

@property (nonatomic, retain) NSArray *viewControllers;

基于此，让我们分析一下您的代码片段的保留计数：

// controllers -> retainCount == 0
NSMutableArray *controllers = [[NSMutableArray alloc] init]; // controllers (alloc) -> retainCount++ == +1
for (unsigned i = 0; i < kNumberOfPages; i++) {
    [controllers addObject:[NSNull null]];
}
self.viewControllers = controllers; // controllers (retained by viewControllers) -> retainCount++ == +2
[controllers release]; // controllers (released) == retainCount-- == +1

稍后......

- (void)dealloc {
    [self.viewControllers release]; // controllers (released) -> retainCount-- == 0 (zero == no leak == no crash by over-release)
    ...
}