NSPointerArray 奇怪的压缩

Question

我有一个较弱的 NSPointerArray，其中一些 NSObject 已发布。在调用 compact 之前，我看到的是：

(lldb) po [currentArray count]
1
(lldb) po [currentArray pointerAtIndex:0]
<nil>
(lldb) po [currentArray allObjects]
<__NSArrayM 0x16f04f00>(

)

这是有道理的，但真正奇怪的是，当我对该数组调用 compact 时，我看到了相同的值！计数仍然 returns 1 和 pointerAtIndex:0 是 nil.

为什么没有删除 nil？

编辑

这是完整的代码（是的，它是 XCTesting 框架）：

- (void)testCompaction {
    __weak id testingPointer = nil;

    NSPointerArray *weakArray = [NSPointerArray weakObjectsPointerArray];

    @autoreleasepool {

        NSObject *someObj = [[NSObject alloc] init];

        testingPointer = someObj;

        [weakArray addPointer:(__bridge void*)testingPointer];

        NSLog(@"before compaction inside autorelease: testingPointer = %@ count = %d, allObjects = %@, pointerAtIndex:0 = %@, pointerAtIndex:0 class = %@", testingPointer, [weakArray count], [weakArray allObjects], [weakArray pointerAtIndex:0], [(id)[weakArray pointerAtIndex:0] class]);

        someObj = nil;
    }

    NSLog(@"before compaction outside autorelease: testingPointer = %@ count = %d, allObjects = %@, pointerAtIndex:0 = %@, pointerAtIndex:0 class = %@", testingPointer, [weakArray count], [weakArray allObjects], [weakArray pointerAtIndex:0], [(id)[weakArray pointerAtIndex:0] class]);

    [weakArray compact];

    NSLog(@"after compaction outside autorelease: testingPointer = %@ count = %d, allObjects = %@, pointerAtIndex:0 = %@, pointerAtIndex:0 class = %@", testingPointer, [weakArray count], [weakArray allObjects], [weakArray pointerAtIndex:0], [(id)[weakArray pointerAtIndex:0] class]);
}

和日志：

  before compaction inside autorelease: testingPointer = <NSObject: 0x7de7ff80> count = 1, allObjects = (
    "<NSObject: 0x7de7ff80>"
), pointerAtIndex:0 = <NSObject: 0x7de7ff80>, pointerAtIndex:0 class = NSObject
2015-07-20 14:27:14.062 AppetizeSuite copy[54144:9019054] before compaction outside autorelease: testingPointer = (null) count = 1, allObjects = (
), pointerAtIndex:0 = (null), pointerAtIndex:0 class = (null)
2015-07-20 14:27:22.615 AppetizeSuite copy[54144:9019054] after compaction outside autorelease: testingPointer = (null) count = 1, allObjects = (
), pointerAtIndex:0 = (null), pointerAtIndex:0 class = (null)

为什么compact方法不删除第一个指针？在调用 compact.

之前显然是 nil

Answer 1

我见过同样的行为。这是一个开放的雷达错误报告： http://www.openradar.me/15396578

Answer 2

发生这种情况的原因是 -compact 首先检查是否设置了内部标志 'needsCompaction'。如果不是，它就会提前退出。设置标志的唯一时间是通过 public 接口将 nil 指针直接插入数组。如果在将指针插入数组后释放弱引用对象（并且指针为零），则不会设置它。

针对此行为的一个解决方法是在调用 -compact 之前有目的地向数组附加一个 nil 指针。不理想，但它会工作。

[pa addPointer:nil]; // forces the pointer array to do compaction next time
[pa compact];

Answer 3

已经几年了，使用示例代码显示没有任何变化。

但是，当使用方法 -replacePointerAtIndex:withPointer:

执行指针更新时，-compact 工作正常

在上面的代码中，替换

someObj = nil;

来自

 [weakArray replacePointerAtIndex:0 withPointer:nil];

在 [weakArray compact]; 之后提供了预期的结果，代码将在最后一个 NSLog

处崩溃

NSPointerArray 奇怪的压缩

NSPointerArray weird compaction

objective-c

automatic-ref-counting

nspointerarray