NSPointerArray奇怪的压缩

Question

有NSPointerArray一些NSObject已被释放的弱者.在打电话给compact我看之前是:

(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,当我调用compact该数组时,我看到了相同的值!计数仍然返回1并且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？这显然是nil在召唤之前compact.

Answer 1

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,它只是提前保释.设置标志的唯一时间是nil指针是否通过公共接口直接插入到数组中.如果在将指针插入数组后释放弱引用对象(并且指针为nil'd),则不会设置它.

解决此问题的一种方法是在调用之前有目的地向数组附加一个nil指针-compact.不理想,但它会工作.

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

Answer 2

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