ios - 从核心数据中检索 NSDate

Question

我正在尝试从核心数据中检索最新的 NSdate 条目。我尝试这样做的方法是按日期排序并获取objectAtIndex。然而，我正在努力检索结果，并将其返回为 nil。我认为我的问题与 NSDate *obj = [results objectAtIndex:0]; 相关，尽管我不确定如何解决它。任何建议都将受到欢迎。我可能会偏离目标，所以请原谅我。

- (void)viewDidLoad
{
    [super viewDidLoad];
    //Get Reference to App Delegate
    SSAppDelegate *appDelegate = [UIApplication sharedApplication].delegate;
    NSManagedObjectContext *context = [appDelegate managedObjectContext];
    //Fetch Entity
    NSFetchRequest *request = [[NSFetchRequest alloc]
                              initWithEntityName:@"RecentDetails"];
    //Sort By Date
    NSSortDescriptor *sort = [[NSSortDescriptor alloc]initWithKey:@"date" ascending:NO];
    [request setSortDescriptors:[NSArray arrayWithObject:sort]];
    //Store In Array
     NSArray *results = [context executeFetchRequest:request error:NULL];

/////////////NEEDS EXTRA HERE ACCORDING TO COMMENTS


    //Find Object at Index 0
    NSDate *obj = [results objectAtIndex:0];
    //Set Batch Size
    [request setFetchBatchSize:1];

    //NSDate Formatter
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"ddMMyyyy"];

    //Convert to string
    NSString *stringFromDate = [dateFormatter stringFromDate:obj];

    //Test Log
    NSLog(@"Latest Date! %@", stringFromDate);

}

Answer 1

• 插入时，更改:

  NSManagedObjectContext *recentDetails = [NSEntityDescription insertNewObjectForEntityForName:@"RecentDetails"inManagedObjectContext:context];
  

  到:

  NSManagedObject *recentDetails = [NSEntityDescription insertNewObjectForEntityForName:@"RecentDetails"inManagedObjectContext:context];`
  

• 在检索时，正如 Stakenborg 所指出的那样，您应该从“RecentDetails”实体对象中获取日期属性。

• [request setFetchBatchSize:1] 应在 [contextexecuteFetchRequest:request...] 之前设置，否则对RecentDetails 数量没有影响已获取对象。