Question

我在视图控制器之间传递数据时遇到问题。

所有三个视图控制器都是表视图。

 WorkoutTypeVC
 WorkoutSetVC
 WorkoutExerciseVC

我有三个实体，

WorkoutType
    workouts(->WorkoutSet) One to Many
WorkoutSet
    exercises(->WorkoutExercise) One to Many
    workoutType(->WorkoutType) Inverse
WorkoutExercise
    workoutSet(->WorkoutSet) Inverse

我可以在所有三个视图控制器之间切换，WorkoutTypeVC正确加载正确显示所有条目，当选择WorkoutSetVC时，加载显示与WorkoutTypeVC选择对应的正确条目。

但是当我从WorkoutSetVC中选择一个条目时，WorkoutExerciseVC会加载但是为空，甚至不会加载选择的标题。

我使用了从WorkoutTypeVC和WorkoutSetVC切换时使用的相同代码。

以下是在WorkoutType.m文件中切换视图的代码：

-(void)fetchWorkoutTypes
{
    NSFetchRequest *fetchRequest =
    [NSFetchRequest fetchRequestWithEntityName:@"WorkoutType"];
    NSString *cacheName = [@"WorkoutType" stringByAppendingString:@"Cache"];
    NSSortDescriptor *sortDescriptor =
    [NSSortDescriptor sortDescriptorWithKey:@"workoutType" ascending:YES];
    [fetchRequest setSortDescriptors:@[sortDescriptor]];
    self.fetchedResultsController = [[NSFetchedResultsController alloc]
                                 initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext
                                 sectionNameKeyPath:nil cacheName:cacheName];
    NSError *error;
    if (![self.fetchedResultsController performFetch:&error])
    {
        NSLog(@"Fetch failed: %@", error);
    }
}

- (void)viewDidAppear:(BOOL)animated{

    [self fetchWorkoutTypes];
    [self.tableView reloadData];
}
 - (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{

    // Return the number of sections.
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{

    // Return the number of rows in the section.
    return self.fetchedResultsController.fetchedObjects.count;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";
    UITableViewCell *cell =
    [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil)
    {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleValue1
                                  reuseIdentifier:CellIdentifier];
        cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;
    }

    WorkoutType *workoutType = (WorkoutType *)[self.fetchedResultsController
                                        objectAtIndexPath:indexPath];
    cell.textLabel.text = workoutType.workoutType;
    cell.detailTextLabel.text = [NSString stringWithFormat:@"(%d)", workoutType.workouts.count];

    return cell;
}

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    WorkoutType *workoutType = (WorkoutType *)[self.fetchedResultsController objectAtIndexPath:indexPath];
    WorkoutSetViewController *detailViewController = [[WorkoutSetViewController alloc] initWithWorkoutType:workoutType];

    [self.navigationController pushViewController:detailViewController animated:YES];

}

以下是WorkoutSetVC.m

的代码

-(void)fetchWorkoutSets
{
    NSFetchRequest *fetchRequest =
    [NSFetchRequest fetchRequestWithEntityName:@"WorkoutSet"];
    NSString *cacheName = [@"WorkoutSet" stringByAppendingString:@"Cache"];
    NSSortDescriptor *sortDescriptor =
[NSSortDescriptor sortDescriptorWithKey:@"workoutName" ascending:YES];
    [fetchRequest setSortDescriptors:@[sortDescriptor]];
    self.fetchedResultsController = [[NSFetchedResultsController alloc]
                                 initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext
                                 sectionNameKeyPath:nil cacheName:cacheName];
    NSError *error;
    if (![self.fetchedResultsController performFetch:&error])
    {
        NSLog(@"Fetch failed: %@", error);
    }
}
- (id)initWithWorkoutType:(WorkoutType *)workoutType
{
    self = [super initWithStyle:UITableViewStylePlain];
    if (self)
    {
        self.workoutType = workoutType;
    }
    return self;
}
- (void)viewDidLoad
{
    [super viewDidLoad];

    self.title = self.workoutType.workoutType;

    [self fetchWorkoutSets];
}
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    // Return the number of sections.
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    // Return the number of rows in the section.
    return self.workoutType.workouts.count;
}


- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";
    UITableViewCell *cell =
    [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil)
    {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle
                                  reuseIdentifier:CellIdentifier];
        cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;
    }
    WorkoutSet *workoutSet = [self.workoutType.workouts.allObjects objectAtIndex:indexPath.row];
    cell.textLabel.text = workoutSet.workoutName;
    cell.detailTextLabel.text = [NSString stringWithFormat:@"(%d)", workoutSet.exercises.count];
    return cell;
}
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    WorkoutSet *workoutSet = (WorkoutSet *)[self.fetchedResultsController objectAtIndexPath:indexPath];
    WorkoutExerciseTableViewController *detailViewController = [[WorkoutExerciseTableViewController alloc] initWithWorkoutSet:workoutSet];

    [self.navigationController pushViewController:detailViewController animated:YES];
}

以下是WorkoutExercise.m

的代码

- (id)initWithWorkoutSet:(WorkoutSet *)workoutSet
{
    self = [super initWithStyle:UITableViewStylePlain];
    if (self)
    {
        self.workoutSet = workoutSet;
    }
    return self;
}

-(void)fetchWorkoutExercises
{
    NSFetchRequest *fetchRequest =
   [NSFetchRequest fetchRequestWithEntityName:@"WorkoutExercise"];
   NSString *cacheName = [@"WorkoutExercise" stringByAppendingString:@"Cache"];
    NSSortDescriptor *sortDescriptor =
    [NSSortDescriptor sortDescriptorWithKey:@"exerciseName" ascending:YES];
    [fetchRequest setSortDescriptors:@[sortDescriptor]];
    self.fetchedResultsController = [[NSFetchedResultsController alloc]
                                 initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext
                                 sectionNameKeyPath:nil cacheName:cacheName];
    NSError *error;
    if (![self.fetchedResultsController performFetch:&error])
    {
        NSLog(@"Fetch failed: %@", error);
    } 
 }

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.title = self.workoutSet.workoutName;
    [self fetchWorkoutExercises];

}


- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";
    UITableViewCell *cell =
[tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil)
    {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle
                                  reuseIdentifier:CellIdentifier];
        cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;
    }
    WorkoutExercise *exercise = [self.workoutSet.exercises.allObjects objectAtIndex:indexPath.row];

    cell.textLabel.text = exercise.exerciseName;

    return cell;
}

不确定我需要为第三个视图控制器列出所有条目，甚至第三个视图控制器的标题也不会加载在ViewDidLoad方法中编码。

谢谢

Answer 1

问题是（我假设）在第二个（和第三个？）中数据源的使用不一致查看控制器。

在WorkoutSetViewController中，cellForRowAtIndexPath直接通过self.workoutType.workouts.allObjects访问对象，但didSelectRowAtIndexPath使用获取的结果控制器（FRC）。这根本不符合逻辑。如果表视图由FRC驱动，则所有数据源方法都必须使用FRC。

在第二个视图控制器中，self.fetchedResultsController可能是nil？然后传递给第三个视图控制器的workoutSet将是nil，这将是说明没有设置标题，也没有显示任何对象。

使用self.workoutType.workouts从allObjects生成数组也存在问题，因为数组元素的顺序可以是随机的。

第二个视图控制器应使用提取的结果控制器来显示与给定WorkoutSet相关的所有workoutType个对象。

第三个视图控制器应使用获取的结果控制器来显示与给定WorkoutExercise相关的所有workoutSet个对象。

WorkoutSetVC.m中的

更新： fetchWorkoutSets应如下所示：

-(void)fetchWorkoutSets
{
    NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"WorkoutSet"];
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"workoutType = %@", self.workoutType];
    [fetchRequest setPredicate:predicate];
    NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"workoutName" ascending:YES];
    [fetchRequest setSortDescriptors:@[sortDescriptor]];
    self.fetchedResultsController = [[NSFetchedResultsController alloc]
                                 initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext
                                 sectionNameKeyPath:nil cacheName:nil];
    self.fetchedResultsController.delegate = self;
    NSError *error;
    if (![self.fetchedResultsController performFetch:&error])
    {
        NSLog(@"Fetch failed: %@", error);
    }
}

谓词对于仅提取与self.workoutType相关的训练集非常重要。

同样，WorkoutExercise.m中的fetchWorkoutExercises将使用谓词

    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"workoutSet = %@", self.workoutSet];
    [fetchRequest setPredicate:predicate];

仅提取与self.workoutSet相关的练习。

对于数据源方法，请查看NSFetchedResultsController documentation，它包含您可以复制的示例代码并适应您的需求。或者使用“Master-Detail Application”模板创建一个全新的Xcode iOS应用程序，然后选中“Core Data”复选框。那也会给你示例代码。

例如，在WorkoutSetVC.m中的cellForRowAtIndexPath中，您将替换

WorkoutSet *workoutSet = [self.workoutType.workouts.allObjects objectAtIndex:indexPath.row];

通过

WorkoutSet *workoutSet = [self.fetchedResultsController objectAtIndexPath:indexPath];

在视图控制器之间传递一个到多个核心数据

1 个答案: