添加对象到什么类型的变量？

Question

我将使用这种方法将锻炼实体添加到例程中。我如何声明 SelectedRoutine 以及它是什么类型？我想我将其设置在此表的父表的 didSelectRow 方法中。

-(void)addExercise
{   
    NSError *error = nil;

    Exercise *exercise = (Exercise *)[NSEntityDescription insertNewObjectForEntityForName:@"Exercise" inManagedObjectContext:managedObjectContext];

    exercise.name = selectedExercise;

    [theSelectedRoutine addExerciseObject: exercise];

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

    [self.routineTableView reloadData];
}

Answer 1

有几种解决方案。首先，如果您不想为托管对象使用子类，您可以获取关系的可变集并向其中添加新的练习。

-(void)addExercise
{   
  NSError *error = nil;
  Exercise *exercise = [NSEntityDescription insertNewObjectForEntityForName:@"Exercise" inManagedObjectContext:managedObjectContext];
  [exercise setName:selectedExercise];
  [[theSelectedRoutine mutableSetForKey:@"exercise"] addObject:exercise];

  if (![managedObjectContext save:&error]) {
    NSLog(@"Failed to save: %@\n%@", [error localizedDescription], [error userInfo]);
  }

  [[self routineTableView] reloadData];
}

另一个目标是为您的例程创建一个子类：

@interface Routine : NSManagedObject

- (void)addExerciseObject:(NSManagedObject*)exercise;

@end

@implementation Routine

- (void)addExerciseObject:(Employee *)value
{
    NSSet *changedObjects = [[NSSet alloc] initWithObjects:&value count:1];
    NSMutableSet *primitiveEmployees = [self primitiveValueForKey:@"exercise"];

    [self willChangeValueForKey:@"exercise" withSetMutation:NSKeyValueUnionSetMutation usingObjects:changedObjects];
    [[self primitiveEmployees] addObject:value];
    [self didChangeValueForKey:@"exercise" withSetMutation:NSKeyValueUnionSetMutation usingObjects:changedObjects];

    [changedObjects release];
}

@end

然后您可以从那里直接调用 -addExerciseObject:。

-(void)addExercise
{   
  NSError *error = nil;
  Exercise *exercise = [NSEntityDescription insertNewObjectForEntityForName:@"Exercise" inManagedObjectContext:managedObjectContext];
  [exercise setName:selectedExercise];
  [theSelectedRoutine addExerciseObject:exercise];

  if (![managedObjectContext save:&error]) {
    NSLog(@"Failed to save: %@\n%@", [error localizedDescription], [error userInfo]);
  }

  [[self routineTableView] reloadData];
}

请注意，无论哪种情况，您不需要都需要从 -insertNewObjectForEntityForName: inManagedObjectContext: 中设置锻炼对象的大小写。该调用的返回结果是 id，并且 id 永远不需要进行强制转换。一般来说，Objective-C 中的类型转换是错误的。