Question

我有一个弱NSPointerArray，其中一些NSObject已被释放。在致电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，当我在该数组上调用compact时，我看到了相同的值！计数仍返回1，pointerAtIndex:0为nil。

为什么没有删除nil？

修改

这里是完整的代码（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方法不会删除第一个指针？在致电nil之前，它显然是compact。

Answer 1

发生这种情况的原因是-compact首先检查内部标志是否需要压缩＆＃39;已设定。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＆lt; d; d），则不会设置它。

解决此问题的一个方法是在调用-compact之前有目的地向数组附加一个nil指针。不理想，但它会起作用。

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

Answer 2

我已经看到了同样的行为。这是一个开放的雷达错误报告： http://www.openradar.me/15396578

Answer 3

已经有几年了，使用示例代码显示没有变化。

但是，当使用-replacePointerAtIndex：withPointer方法执行指针更新时，-compact可以完美地工作：

在上面的代码中，替换

someObj = nil;

通过

 [weakArray replacePointerAtIndex:0 withPointer:nil];

提供[weakArray compact];之后的预期结果，并且代码将在最后一个NSLog崩溃

NSPointerArray奇怪的压缩

3 个答案: