EXC_BAD_ACCESS 目标-c 块

Question

我在我的 viewDidLoad 方法中运行此代码以从 Firebase 获取数据并将其放入 UIPageViewController

@interface MapViewController () <RoutesPageDelegate>
@property (weak, nonatomic) IBOutlet MKMapView *mapView;
@property (weak, nonatomic) RoutesPageViewController *routesPageViewController;
@property (weak, nonatomic) FIRFirestore *db;
@end

@implementation MapViewController

- (void) viewDidLoad {
    [super viewDidLoad];

    self.db = [FIRFirestore firestore];

    for (UIViewController *obj in self.childViewControllers) {
        if ([obj isKindOfClass:[RoutesPageViewController class]]) {
            self.routesPageViewController = (RoutesPageViewController *)obj;
            self.routesPageViewController.routesPageDelegate = self;
        }
    }

    FIRCollectionReference *routesRef = [self.db collectionWithPath:@"routes"];
    [routesRef getDocumentsWithCompletion:^(FIRQuerySnapshot * _Nullable snapshot, NSError * _Nullable error) {
        if (error != nil) {
            // TODO: handle error
        } else {
            NSMutableArray<RouteModel*> *routes = [NSMutableArray array];

            // For each route
            for (FIRDocumentSnapshot *document in snapshot.documents) {
                RouteModel *route = [[RouteModel alloc] init];
                route.title = document.data[@"title"];
                route.color = document.data[@"color"];
                route.city = document.data[@"city"];

                [routes addObject:route];
            }

            [self.routesPageViewController setRoutes:routes];
        }
    }];


}

这就是调用的 setRoutes 方法：

- (void) setRoutes:(NSMutableArray<RouteModel *> *)routes {
    self.routes = routes;

    NSMutableArray<RoutePageViewController *> * routeViewControllers = [NSMutableArray array];
    for (RouteModel * route in routes) {
        [routeViewControllers addObject:[self viewControllerAtIndex:[routes indexOfObject:route]]];
    }

    [self setViewControllers:routeViewControllers direction:UIPageViewControllerNavigationDirectionForward animated:NO completion:nil];
}

当setRoutes 方法被执行时，它会抛出下图中的错误，说它不能取消引用它：

setRoutes 方法在块内执行。

我得到了这个奇怪的线程堆栈：

我该如何解决这个问题？

Answer 1

你的问题在这里：

- (void) setRoutes:(NSMutableArray<RouteModel *> *)routes {
    self.routes = routes;

调用self.routes 隐式调用设置器setRoutes，这会导致递归无限调用，如您的堆栈所示。

Answer 2

在将块传递给getDocumentsWithCompletion 方法执行时，routes 数组已经被释放并设置为nil，因为没有人将它保留在块之外的任何地方。

您应该将它移动到块中或将其声明为类属性，这样它就不会在类实例处于活动状态时被抛出内存。

[routesRef getDocumentsWithCompletion:^(FIRQuerySnapshot *snapshot, NSError *error) {
    NSMutableArray<RouteModel*> *routes = [NSMutableArray array];
    ...
    [self.routesPageViewController setRoutes:routes];
}];

更新后：

执行self.routes = routes 会调用setRoutes:，这反过来又会导致您的代码出现循环。您应该将其更改为：

- (void)setRoutes:(NSMutableArray<RouteModel *> *)routes {
  if (_routes != routes) {
    _routes = routes;
    ...
  }
}