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为什么我会得到一个不同的 HistoryViewController 实例，而不是我实例化并推送到 navigationController 上的实例？

创建的不同实例没有我设置的任何属性。

ProfileHomeViewController.m

HistoryViewController *historyViewController = nil;
historyViewController = [[HistoryViewController alloc] initWithNibName:@"HistoryViewController" bundle:nil];
// nib has identity of NSObject (I also tried HistoryViewController), and tableviewcontroller with identity HistoryViewController
historyViewController.profile = self.profile;

NSLog(@"%@ > %@", self, self.managedObjectContext);
// <ProfileHomeViewController: 0x5b34330> > <NSManagedObjectContext: 0x7918770>


historyViewController.managedObjectContext = self.managedObjectContext;
NSLog(@"%@ > %@", historyViewController, historyViewController.managedObjectContext);
// <HistoryViewController: 0x792a870> > <NSManagedObjectContext: 0x7918770>

[self.navigationController pushViewController:historyViewController animated:YES];
[historyViewController release];

HistoryViewController.h

@interface HistoryViewController : UITableViewController {

    NSManagedObject *profile;
    NSFetchedResultsController *fetchedResultsController;
    NSManagedObjectContext *managedObjectContext;

}

@property (nonatomic, retain) NSManagedObject *profile;
@property (nonatomic, retain) NSFetchedResultsController *fetchedResultsController;
@property (nonatomic, retain) NSManagedObjectContext *managedObjectContext;

历史视图控制器.m

@implementation HistoryViewController

@synthesize profile;
@synthesize fetchedResultsController;
@synthesize managedObjectContext;


- (void)viewDidLoad {
    [super viewDidLoad];

    NSLog(@"inside HistoryViewController %@ > profile %@", self, self.profile);
    // inside HistoryViewController <HistoryViewController: 0x7917750> > profile (null)

    NSLog(@"inside HistoryViewController %@ > managedObjectContext %@", self, self.managedObjectContext);
    // inside HistoryViewController <HistoryViewController: 0x7917750> > managedObjectContext (null)

    if(self.managedObjectContext == nil){
            NSLog(@"invalid managedObjectContext WTF");
            abort();
    }
}
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1 回答 1

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实例是相同的，对同一实例的引用是不同的（这很好）。

在设置变量之前调用 viewDidLoad 方法，这就是 self.managedObjectContext == nil 的原因。

要么编写一个自定义 init 方法，该方法采用参数 history 和 managedobjectcontext 并将它们设置在 init 中。或者不使用 viewDidLoad，而是使用 viewWillAppear:animated...

于 2010-07-02T18:42:29.200 回答