UISplitViewController在iOS 9中是否存在保留周期错误？

Question

在下面的示例中,我将呈现一个UIViewController具有UIStackViewController其子项的示例:

UIViewController *splitViewParentVC = UIViewController.new;

UIViewController *masterVC = UIViewController.new;
UIViewController *detailVC = UIViewController.new;

UISplitViewController *splitViewController = [[UISplitViewController alloc] init];
splitViewController.viewControllers = @[masterVC, detailVC];

[splitViewParentVC addChildViewController:splitViewController];
[splitViewParentVC.view addSubview:splitViewController.view];
[splitViewController didMoveToParentViewController:splitViewParentVC];
splitViewController.view.frame = splitViewParentVC.view.bounds;
splitViewController.view.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;

__weak UISplitViewController *wSplitViewController = splitViewController;

[self presentViewController:splitViewParentVC animated:YES completion:nil];

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
    [self dismissViewControllerAnimated:YES completion:^{
        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
            if (wSplitViewController) {
                NSLog(@"the split view controller has leaked");
            } else {
                NSLog(@"the split view controller didn't leak");
            }
        });
    }];
});

在iOS 9和9.1中,将打印上面的代码the split view controller has leaked,表明UIStackViewController已泄露(更重要的是,它也泄漏了其主视图和详细视图控制器).

Answer 1

是的，Apple 工作人员已确认iOS 9 中存在保留周期错误。

我测试过，iOS 8.4 中不存在保留周期，但 iOS 9.0 和 9.1 中确实存在。从 iOS 9.2 开始，泄漏似乎已经修复（在 iOS 9.2 模拟器上的 Xcode 7.2 beta 2 中进行了测试）我已经整理了一个示例项目，以轻松确认 UISplitViewController 是否导致自身泄漏（只需运行它并检查控制台）输出）。

这还测试了允许释放主视图控制器和详细视图控制器的尝试。UISplitViewController正如我们所看到的，即使主视图控制器从数组属性中删除，它似乎仍然被保留UISplitViewController.viewControllers。

以下是示例项目中的代码：

- (void)viewDidLoad {
    [super viewDidLoad];

    [self testSplitViewControllerRetainCycleWithCompletion:^{
        [self testManuallyFreeingUpMasterAndDetailViewControllers];
    }];
}

- (void)testSplitViewControllerRetainCycleWithCompletion:(void (^)())completion {

    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{

        UIViewController *splitViewParentVC = UIViewController.new;

        UIViewController *masterVC = UIViewController.new;
        UIViewController *detailVC = UIViewController.new;

        UISplitViewController *splitViewController = [[UISplitViewController alloc] init];
        splitViewController.viewControllers = @[masterVC, detailVC];
        splitViewController.preferredDisplayMode = UISplitViewControllerDisplayModeAllVisible;
        splitViewController.preferredPrimaryColumnWidthFraction = 0.3125; // 320 / 1024
        splitViewController.minimumPrimaryColumnWidth = 100;

        [splitViewParentVC addChildViewController:splitViewController];
        [splitViewParentVC.view addSubview:splitViewController.view];
        [splitViewController didMoveToParentViewController:splitViewParentVC];
        splitViewController.view.frame = splitViewParentVC.view.bounds;
        splitViewController.view.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;

        __weak UISplitViewController *wSplitViewController = splitViewController;
        __weak UIViewController *wMaster = masterVC;
        __weak UIViewController *wDetail = detailVC;

        [self presentViewController:splitViewParentVC animated:YES completion:nil];

        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
            [self dismissViewControllerAnimated:YES completion:^{
                dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
                    if (wSplitViewController) {
                        NSLog(@"the split view controller has leaked");
                    } else {
                        NSLog(@"the split view controller didn't leak");
                    }
                    if (wMaster) {
                        NSLog(@"the master view controller has leaked");
                    } else {
                        NSLog(@"the master view controller didn't leak");
                    }
                    if (wDetail) {
                        NSLog(@"the detail view controller has leaked");
                    } else {
                        NSLog(@"the detail view controller didn't leak");
                    }

                    completion();
                });
            }];
        });
    });
}

- (void)testManuallyFreeingUpMasterAndDetailViewControllers {

    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{

        UIViewController *splitViewParentVC = UIViewController.new;

        UIViewController *masterVC = UIViewController.new;
        UIViewController *detailVC = UIViewController.new;

        UISplitViewController *splitViewController = [[UISplitViewController alloc] init];
        splitViewController.viewControllers = @[masterVC, detailVC];
        splitViewController.preferredDisplayMode = UISplitViewControllerDisplayModeAllVisible;
        splitViewController.preferredPrimaryColumnWidthFraction = 0.3125; // 320 / 1024
        splitViewController.minimumPrimaryColumnWidth = 100;

        [splitViewParentVC addChildViewController:splitViewController];
        [splitViewParentVC.view addSubview:splitViewController.view];
        [splitViewController didMoveToParentViewController:splitViewParentVC];
        splitViewController.view.frame = splitViewParentVC.view.bounds;
        splitViewController.view.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;

        __weak UIViewController *wMaster = masterVC;
        __weak UIViewController *wDetail = detailVC;

        [self presentViewController:splitViewParentVC animated:YES completion:nil];

        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
            [self dismissViewControllerAnimated:YES completion:nil];

            splitViewController.viewControllers = @[UIViewController.new, UIViewController.new];

            dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
                if (wMaster) {
                    NSLog(@"the master view controller has STILL leaked even after an attempt to free it");
                } else {
                    NSLog(@"the master view controller didn't leak");
                }
                if (wDetail) {
                    NSLog(@"the detail view controller has STILL leaked even after an attempt to free it");
                } else {
                    NSLog(@"the detail view controller didn't leak");
                }
            });
        });
    });
}

更新：泄漏似乎从 iOS 9.2 开始得到修复（在 iOS 9.2 模拟器上的 Xcode 7.2 beta 2 中进行了测试）