Iphone 我需要帮助以更好的逻辑重新构造我的方法

更新：

我对这种方法有这样的问题： 默认情况下，除非用户手动更改日期，否则视图会将日期设置为今天，并创建一个以今天的日期作为时间戳的会话

如果我在今天的日期加上运动，一切都很好

如果我选择了一个前一个日期并添加了一个练习，这似乎很好，但似乎练习不仅添加到了前一个日期，而且还添加到了今天

因此，无论我选择之前的日期，exercise实体都会添加到该会话和今天的会话中

因此，当我在tableview中查看今天的会话时，它已经完成了所有练习，因为所有内容都添加到了今天以及手动选择的日期

我怎样才能解决这个问题

原件：

我有一个detailViewController，负责处理核心数据对象会话、练习和设置

该视图的目的是让用户输入有关其健身训练的详细信息。默认情况下，日期设置为今天，但用户可以将其更改为以前的日期。在

createSession

中，当用户按该日期的“完成”按钮时，如果该日期不存在，将创建一个具有该日期时间戳的新会话对象。如果它已经存在，它将获取带有该时间戳日期的对象

问题是，即使用户以后没有输入必要的数据，这也会创建一个新的会话对象。创建训练后，系统会提示用户输入用于训练的重量和重复次数。如果用户未输入此信息（对象集），则存在一个会话对象，该对象没有任何用途，因为它们没有与之相关的练习和设置对象

但我在检查权重/rep之前创建会话对象的原因是，如果获取会话，我希望在视图中显示其属性数据，因此我需要在添加集合/rep之前使用它

我目前的代码是：

    -(void)createSession
{
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    [fetchRequest setPredicate:[NSPredicate predicateWithFormat: @"(timeStamp >= %@ && timeStamp <= %@)", targetDateBegins, targetDateEnds]];
    [fetchRequest setEntity:[NSEntityDescription entityForName:@"Session" inManagedObjectContext:managedObjectContext]];

    NSError *error = nil;
    NSArray *results = [managedObjectContext executeFetchRequest:fetchRequest error:&error];
    NSLog(@"Fetch error: %@", error);

    if ([results count])
    {
        session = (Session *)[results objectAtIndex:0];
    }
    else
    {
        session = (Session *)[NSEntityDescription insertNewObjectForEntityForName:@"Session" inManagedObjectContext:managedObjectContext];
        session.timeStamp = self.picker.date;
    }

    NSSet *filteredExercisesFromSession=[session.exercises filteredSetUsingPredicate:[NSPredicate predicateWithFormat: @"name == %@",selectedExerciseName]];
    if ([filteredExercisesFromSession count] > 0)
    {
        self.exercise=[filteredExercisesFromSession anyObject];
    }
    else
    {
        self.exercise = (Exercise *)[NSEntityDescription insertNewObjectForEntityForName:@"Exercise" inManagedObjectContext:managedObjectContext];
        self.exercise.name = selectedExerciseName;
        [session addExercisesObject:exercise];
    }

    if (![managedObjectContext save:&error])
    {
        // Handle the error.
    }
    NSLog(@"Save error: %@", error);

    [fetchRequest release];
    self.fetchedResultsController = nil;
    [setsTableView reloadData];
}

-(IBAction)createSet
{
    Set *set = (Set *)[NSEntityDescription insertNewObjectForEntityForName:@"Set" inManagedObjectContext:managedObjectContext];
    set.weight = [NSNumber numberWithFloat:weightSelected2];
    set.reps = [NSNumber numberWithInt:repSelected];
    set.timeStamp = self.picker.date;
    [self.exercise addSetsObject:set];

    NSError *error = nil;
    if (![managedObjectContext save:&error])
    {
        // Handle the error.
    }
    NSLog(@"error: %@", error);
    self.fetchedResultsController = nil;
    [setsTableView reloadData];
}

-（void）createSession
{
NSFetchRequest*fetchRequest=[[NSFetchRequest alloc]init]；
[fetchRequest setPredicate:[NSPredicate predicateWithFormat:@”（时间戳>=%@&&timeStamp=%@&&timeStamp这可能比我想写的要脏一点，但它应该能让您很好地了解我对如何解决问题的看法

//Session.m
//Check out the link to PSFoundation and the ActiveRecord Core Data methods
//https://github.com/steipete/PSFoundation/tree/master/activerecord-coredata  

NSString * const kSessionLeavingActiveSession = @"kSessionLeavingActiveSession";
NSString * const kSessionChangingActiveSession = @"kSessionChangingActiveSession";

static Session *activeSession = nil;
@implementation Session

// ....

// a static method to retrieve & create if nil the active session
+ (Session *)activeSession {
    //if activeSession = nil create a new instance
    //reading the code it looks like you only create a new session if there 
    //isn't a session that already exists for the day chosen in the date picker?
    //If that's the case, then it is only possible for there ever to be
    //a single instance of an active session, one which is currently in view.   
}

+ (Session *)sessionForDate:(NSDate *)date andSetActive:(BOOL)isActive {
    //wrap all of your create session logic in here.
    //search for a session that exists for this date, and return it if
    //it exists, or create a new session if it doesn't.

    //send Notification kSessionChangingActiveSession if isActive == YES

    //if isActive is true, set it to the active session. 
}

+ (void)saveOrDestroyActiveSession {
    //register this function as an observer on kSessionChangingActiveSession
    //before the active session is changed, you will be able to determine
    //if the session has anything associated with it, and persist it, or 
    //destroy it.

    //determine if it has exercises assigned to it.

    //if it does, save the context.

    //if it doesn't destroy the active session and set activeSession to nil 
}


+ (void)saveActiveSession {
    //register this function as an observer on kSessionLeavingActiveSession.
    //If you are leaving an area of the application where you are working on
    //the session, you want to send this notification so that you can save
    //the session if you have added exercises.

    //you don't want to delete it though, if you can still go back to the
    //active session, for example, if it's the active session view controller
    //on a tab controller.
}

// the rest of your session methods

@end

//your app delegate
- (void)applicationWillResignActive:(UIApplication *)application {
    //send a notification that you are leaving the active session
}


//viewController.m
//modify your fetched results controller to pull it's list of exercises from the 
//active session, in case it's not saved you can still retrieve the exercises associated
//with it.

- (void)viewDidUnload {
    //send a notification that you are leaving the active session
}

- (void)createSession {
    Session *activeSession = [Session sessionForDate:self.picker.date andSetActive:YES];

    //code to add exercises to session
    //if you've added exercises go ahead and save. 
    //if you haven't let the observers take care of persisting or destroying it.
}

你试过在上问吗？我不知道那个网站，我现在正在查看。谢谢Dear Travis，我尝试实现此代码，但遇到了一些问题。你能帮我完成一下吗？另外，我是否必须添加active record framework类才能使用此代码？我还用你的su中的新代码更新了问题虽然我是一个很好的老师，但我一直在思考如何完成其中的一些。谢谢。
//Session.m
//Check out the link to PSFoundation and the ActiveRecord Core Data methods
//https://github.com/steipete/PSFoundation/tree/master/activerecord-coredata  

NSString * const kSessionLeavingActiveSession = @"kSessionLeavingActiveSession";
NSString * const kSessionChangingActiveSession = @"kSessionChangingActiveSession";

static Session *activeSession = nil;
@implementation Session

// ....

// a static method to retrieve & create if nil the active session
+ (Session *)activeSession {
    //if activeSession = nil create a new instance
    //reading the code it looks like you only create a new session if there 
    //isn't a session that already exists for the day chosen in the date picker?
    //If that's the case, then it is only possible for there ever to be
    //a single instance of an active session, one which is currently in view.   
}

+ (Session *)sessionForDate:(NSDate *)date andSetActive:(BOOL)isActive {
    //wrap all of your create session logic in here.
    //search for a session that exists for this date, and return it if
    //it exists, or create a new session if it doesn't.

    //send Notification kSessionChangingActiveSession if isActive == YES

    //if isActive is true, set it to the active session. 
}

+ (void)saveOrDestroyActiveSession {
    //register this function as an observer on kSessionChangingActiveSession
    //before the active session is changed, you will be able to determine
    //if the session has anything associated with it, and persist it, or 
    //destroy it.

    //determine if it has exercises assigned to it.

    //if it does, save the context.

    //if it doesn't destroy the active session and set activeSession to nil 
}


+ (void)saveActiveSession {
    //register this function as an observer on kSessionLeavingActiveSession.
    //If you are leaving an area of the application where you are working on
    //the session, you want to send this notification so that you can save
    //the session if you have added exercises.

    //you don't want to delete it though, if you can still go back to the
    //active session, for example, if it's the active session view controller
    //on a tab controller.
}

// the rest of your session methods

@end

//your app delegate
- (void)applicationWillResignActive:(UIApplication *)application {
    //send a notification that you are leaving the active session
}


//viewController.m
//modify your fetched results controller to pull it's list of exercises from the 
//active session, in case it's not saved you can still retrieve the exercises associated
//with it.

- (void)viewDidUnload {
    //send a notification that you are leaving the active session
}

- (void)createSession {
    Session *activeSession = [Session sessionForDate:self.picker.date andSetActive:YES];

    //code to add exercises to session
    //if you've added exercises go ahead and save. 
    //if you haven't let the observers take care of persisting or destroying it.
}