Question

在以下示例中，我将展示一个UIViewController作为其子级UIStackViewController：

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，上面的代码将打印the split view controller has leaked，表明UIStackViewController已泄露（更重要的是，它也会泄漏其主视图控制器和详细视图控制器）。

Answer 1

是的，Apple员工在iOS 9中存在保留周期错误confirmed。

我已经测试过iOS 8.4中不存在保留周期，但在iOS 9.0和9.1中确实存在。 从iOS 9.2（在iOS 9.2模拟器上的Xcode 7.2 beta 2中测试）漏洞似乎已经修复了我已经整理了一个sample project来轻松确认是否UISplitViewController导致自己泄漏（只需运行它并检查控制台输出）。

这还测试了允许取消分配主视图控制器和详细视图控制器的尝试。可以看出，即使从UISplitViewController数组属性中删除了主视图控制器，UISplitViewController.viewControllers仍然可以保留主视图控制器。

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：自iOS 9.2（在iOS 9.2模拟器上的Xcode 7.2 beta 2中测试）后漏洞似乎已修复

Answer 2

据我所知，-[UIViewController addChildViewController:] iOS 9.0~9.1中存在内存泄漏问题。所以我认为它不仅仅是UISplitViewController的错误。 Snipets如下，

- (void)viewDidLoad {
    [super viewDidLoad];
    MyFirstViewController *vc = [self.storyboard instantiateViewControllerWithIdentifier:@"MyFirstViewController"];
    [self addChildViewController:vc];
    [self.view addSubview:vc.view];
    [vc didMoveToParentViewController:self];
}

如果你从当前的视图控制器撤退，你会发现没有调用MyFirstViewController的dealloc。

可能的解决方法是在代码中使用storyboard的容器视图而不是addChildViewController。我已经确认Container View的子视图控制器将被正确释放。

另一种解决方法是removeChildViewController:中的-(void)viewDidDisappear:(BOOL)animated。但是，作为苹果的工作人员mentioned，不推荐使用此解决方法。

- (void)viewDidDisappear:(BOOL)animated {
    [super viewDidDisappear:animated];
    NSArray<__kindof UIViewController *> * children = self.childViewControllers;
    for (UIViewController *vc in children) { // not recommended
        [vc willMoveToParentViewController:nil];
        [vc.view removeFromSuperview];
        [vc removeFromParentViewController];
    }
}

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

2 个答案: