如何调试：*** -[<func_name> controllerWillChangeContent:]：消息发送到已释放实例 0x5909c60

Question

我是否错误地声明或使用了“课程”变量？我需要将用户选择的课程对象发送到子 UIViewController 并且没有任何运气。此代码运行 2 次，然后第三次失败。

我得到的运行时错误是：

2011-10-09 17:04:41.403 [] *** -[vcListGrades controllerWillChangeContent:]: message sent to deallocated instance 0x5909c60

当我使用调试器命令“info malloc-history 0x5909c60”找到该地址时，它会将我指向下面显示的代码。

// 这是有问题的代码

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {

    [tableView deselectRowAtIndexPath:(NSIndexPath *)indexPath animated:YES];   

    course  = [_fetchedResultsController objectAtIndexPath:indexPath];  

    //create the new controller for next drill level into table
    vcListGrades *listGradesViewController = [[vcListGrades alloc] initWithNibName:@"vcListGrades" bundle:nil];    

// ^^^ 上面这一行是错误标记的行。

    // take the MO context with you to the next level of table drilling
    listGradesViewController.managedObjectContext = self.managedObjectContext;

    // take the school_courseName record that was just clicked  with you as you drill into next table
    [listGradesViewController setCourse: course];

    // deselect the row that was just clicked - this according to mac style guide
    [tableView deselectRowAtIndexPath:(NSIndexPath *)indexPath animated:YES];

    //push new controller onto stack and go for it
    [self.navigationController pushViewController:listGradesViewController animated:YES];

    [listGradesViewController release];

}

//这是.h文件中如何定义课程

@interface vcListCourses : UITableViewController <NSFetchedResultsControllerDelegate> {

    NSFetchedResultsController *_fetchedResultsController;
    NSManagedObjectContext *managedObjectContext;
    Schoolyear *_schoolyear;
    Course *course;

}

...elipse
@property (nonatomic, retain) Course *course;

//在.m文件中合成行

@synthesize course;

这里是 info malloc-history 堆栈

(gdb) info malloc-history 0x5909c60
Alloc: Block address: 0x05909c60 length: 176
Stack - pthread: 0xacff42c0 number of frames: 19
    0: 0x991e990b in malloc_zone_calloc
    1: 0x991ea837 in calloc
    2: 0x11322d4 in class_createInstance
    3: 0xefe5d8 in +[NSObject(NSObject) allocWithZone:]
    4: 0xefe3da in +[NSObject(NSObject) alloc]
    5: 0x83b6 in -[vcListCourses tableView:didSelectRowAtIndexPath:] at vcListCourses.m:428
    6: 0x36ab68 in -[UITableView _selectRowAtIndexPath:animated:scrollPosition:notifyDelegate:]
    7: 0x360b05 in -[UITableView _userSelectRowAtPendingSelectionIndexPath:]
    8: 0x7279e in __NSFireDelayedPerform
    9: 0xfbb8c3 in __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__
   10: 0xfbce74 in __CFRunLoopDoTimer
   11: 0xf192c9 in __CFRunLoopRun
   12: 0xf18840 in CFRunLoopRunSpecific
   13: 0xf18761 in CFRunLoopRunInMode
   14: 0x19311c4 in GSEventRunModal
   15: 0x1931289 in GSEventRun
   16: 0x301c93 in UIApplicationMain
   17: 0x26e9 in main at main.m:14
   18: 0x2665 in start

这看起来对吗？

我在 rootviewcontroller.h 文件中这样定义我的 nsfetchedResultsController

The @interface RootViewController : UITableViewController  <NSFetchedResultsControllerDelegate> {

    NSFetchedResultsController *_fetchedResultsController;
    NSManagedObjectContext *managedObjectContext;
    UIBarButtonItem *addButton;
    Schoolyear *year;
}

@property (nonatomic, retain) NSFetchedResultsController *fetchedResultsController;

这是我的 NSFetchedResultsController 的 .m 文件

@synthesize fetchedResultsController = _fetchedResultsController;

Answer 1

请显示异常堆栈。当然，您会意识到，当您分配“课程”时，它不会被保留。要保留您需要分配给“self.course”。