Question

我试图围绕CoreData。所以我有一个静态的tableview用于统计信息，标签包括：＆＃34;条目数＆＃34;，＆＃34;总距离＆＃34;，＆＃34;总时间＆＃34;我有我的coredata实体，名为＆＃34; Recording＆＃34;及其属性＆＃34; startDate＆＃34;，＆＃34; duration＆＃34;，...我希望从CURRENT周获取所有条目，然后一方面显示条目数量，另一方面显示条目数量交出总时间。我知道如何设置获取请求（谢谢，谷歌）

- (NSFetchedResultsController *)fetchedResultsController
{
    if (_fetchedResultsController != nil)
    {
        return _fetchedResultsController;
    }

    if (self.managedObjectContext)
    {
        NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
        NSEntityDescription *entity = [NSEntityDescription entityForName:@"Recording" inManagedObjectContext:self.managedObjectContext];
        [fetchRequest setEntity:entity];

        NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"startDate" ascending:NO];
        NSArray *sortDescriptors = [NSArray arrayWithObjects:sortDescriptor, nil];
        [fetchRequest setSortDescriptors:sortDescriptors];

        NSFetchedResultsController *frc = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
                                                                              managedObjectContext:self.managedObjectContext
                                                                                sectionNameKeyPath:nil
                                                                                         cacheName:nil];
    frc.delegate = self;
    self.fetchedResultsController = frc;

    NSError *error = nil;
    if (![self.fetchedResultsController performFetch:&error])
    {
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
    }
return _fetchedResultsController;
}

但是我坚持这个特殊的想法，我甚至不确定我是否需要这样做......

Answer 1

我现在使用：

解决了

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc]init];

NSEntityDescription *theType = [NSEntityDescription entityForName:@"Recording" inManagedObjectContext:self.managedObjectContext];
fetchRequest.entity = theType;

NSDate *firstDayOfCurrentWeek = [self firstWeekday:[NSDate date]];

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"((startDate > %@) AND (startDate <= %@))",firstDayOfCurrentWeek, [NSDate date]];
fetchRequest.predicate = predicate;

NSSortDescriptor *theDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"startDate" ascending:NO];
NSArray *sortDescriptors = [NSArray arrayWithObjects:theDescriptor, nil];

[fetchRequest setSortDescriptors:sortDescriptors];

并找到这样的总和/总数：

NSFetchedResultsController *fetchedResults = self.fetchedResultsController;

NSInteger allWorkouts = [[fetchedResults fetchedObjects] count];

CGFloat totalDistance = [[[fetchedResults fetchedObjects] valueForKeyPath: @"@sum.distance"] floatValue];

感谢谓词提示：）

Answer 2

NSPredicate是您正在搜索的内容。

https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/CoreData/Articles/cdFetching.html

在managedObjectContext中查找特定对象并计算总和

2 个答案: