Question

我编写了一个ios应用程序，以便将数据保存到核心数据，然后使用以下代码获取它：

   NSManagedObjectContext *context = [self managedObjectContext];
NSError *error;

NSManagedObject *failedBankInfo = [NSEntityDescription
                                   insertNewObjectForEntityForName:@"UserData"
                                   inManagedObjectContext:context];
[failedBankInfo setValue:[NSNumber numberWithInt:1] forKey:@"userId"];

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription
                               entityForName:@"UserData" inManagedObjectContext:context];
[fetchRequest setEntity:entity];
NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error];
for (NSManagedObject *info in fetchedObjects) {
     NSLog(@"Name: %@", [info valueForKey:@"userId"]);

}

这里没问题。但在我关闭我的应用程序并将setvalue修改为2之后，我只收到最后一个数据2.早期数据（1）被删除。

即使在我关闭应用程序后，我该怎么做才能保留数据条目。

谢谢！

Answer 1

您需要创建UIManagedDocument以保存核心数据信息。我通常创建UIManagedDocument作为类的属性。对于示例，我创建了一个名为UIManagedDocument的{{1}}：

theManagedDocument

然后我创建了一个名为NSURL *url = [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject]; url = [url URLByAppendingPathComponent:@"DocumentName"]; self.theManagedDocument = [[UIManagedDocument alloc] initWithFileURL:url]; if([[NSFileManager defaultManager] fileExistsAtPath:[url path]]) { [theManagedDocument openWithCompletionHandler:^(BOOL success){ if(success) [self documentIsReady]; if(!success) NSLog(@"Couldn't Open Document"); }]; } else { [theManagedDocument saveToURL:url forSaveOperation:UIDocumentSaveForCreating completionHandler:^(BOOL success){ if(success) [self documentIsReady]; if(!success) NSLog(@"Couldn't Create Document"); }]; }的方法，该方法在成功创建或打开文档时被调用（如果文档已经存在则打开，否则创建）。我还将上下文保留为属性。这里称为documentIsReady。我还在你的代码中添加了：

context

完成后，您将需要关闭文档：

- (void) documentIsReady
{
    if(self.theManagedDocument.documentState == UIDocumentStateNormal) 
    {
        self.context = self.theManagedDocument.managedObjectContext;
        NSError *error;

        NSManagedObject *failedBankInfo = [NSEntityDescription
                               insertNewObjectForEntityForName:@"UserData"
                               inManagedObjectContext:self.context];
        [failedBankInfo setValue:[NSNumber numberWithInt:1] forKey:@"userId"];

        NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
        NSEntityDescription *entity = [NSEntityDescription
                           entityForName:@"UserData" inManagedObjectContext:self.context];
        [fetchRequest setEntity:entity];
        NSArray *fetchedObjects = [self.context executeFetchRequest:fetchRequest error:&error];
        for (NSManagedObject *info in fetchedObjects) {
            NSLog(@"Name: %@", [info valueForKey:@"userId"]);
        }
    }
}

Answer 2

您没有保存新记录。

[self.managedObjectContext save:nil];

关闭应用程序[IOS]后删除数据

2 个答案: