数据表属性未显示在表视图控制器中

Question

我是iOS编程的新手，希望有人可以帮助我解决这个问题......

我正在使用表视图控制器来显示使用数据模型创建的数据表中的内容。 我有一个视图控制器，它连接到表视图控制器，它从创建上下文开始：

- (void)viewDidLoad {
[super viewDidLoad];
//create managed document memory block
NSFileManager *fileManager = [NSFileManager defaultManager];
NSURL *documentsDirectory = [[fileManager URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] firstObject];
NSString *documentName = @"MyDatabaseTest";
NSURL *url = [documentsDirectory URLByAppendingPathComponent:documentName];
UIManagedDocument *document = [[UIManagedDocument alloc] initWithFileURL:url];
//check to see if file already exists
BOOL fileExists = [[NSFileManager defaultManager] fileExistsAtPath:[url path]];
//if yes, do something, if not open/save
if (fileExists) {
    [document openWithCompletionHandler:^(BOOL success) {
        if (success) [self documentIsReady:document];
        if (!success) NSLog(@"couldn't open document at %@", url);
    }];
}  else  {
    [document saveToURL:url forSaveOperation:UIDocumentSaveForCreating completionHandler:^(BOOL success) {
        if (success) [self documentIsReady:document];
        if (!success) NSLog(@"couldn't open document at %@", url);
    }];
}
}
- (void)documentIsReady:(UIManagedDocument *)document  {
if (document.documentState == UIDocumentStateNormal)  {
    NSManagedObjectContext *context = document.managedObjectContext;
    self.context = context;
}
}

然后在 segue 中添加对象：

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
if ([sender isKindOfClass:[UIButton class]])  {
    NSIndexPath *indexPath = sender;
    NSDictionary *currentDictionaryItem = self.projectDictionary;
    NSString *currentName = [currentDictionaryItem valueForKeyPath:@"name"];
    if (indexPath)  {
        if ([segue.identifier isEqualToString:@"TableSegue"])  {
            [segue.destinationViewController setTitle:currentName];
//                NSLog(@"the mutable dictionary includes = %@",currentName);
            [Project newProjectCreation:self.projectDictionary inManagedObjectContext:self.context];
            ProjectsCDTVC *pcdtvc = [[ProjectsCDTVC alloc] init];
            [pcdtvc makeContext:self.context];
        }
    }
  }
}

该对象似乎已正确添加到数据表中，但是当我调用核心数据表视图控制器子类 ProjectsCDTVC 时，cellForRowAtIndexPath 永远不会被调用。 项目CDTVC也被指定为情节提要中表视图控制器的自定义类。

-(void)makeContext:(NSManagedObjectContext *)myContext
{
_managedObjectContext = myContext;
//request into Project table
NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Project"];

//get all projects when predicate is nil
request.predicate = nil;
request.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES selector:@selector(localizedStandardCompare:)]];
request.fetchLimit = 100;
self.fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:request managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:nil];
   NSLog(@"the managed object context is %@",self.managedObjectContext);
} 
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{

UITableViewCell *cell = [self.tableView dequeueReusableCellWithIdentifier:@"Project Cell"];
Project *project = [self.fetchedResultsController objectAtIndexPath:indexPath];
cell.textLabel.text = project.name;
return cell;
}

我看到一篇相关的帖子，指出如果表视图中的部分数为零，则不会调用cellForRowAtIndexPath，所以我观察了部分变量。 部分最初具有正确的值"1"，但在某个时候被重置为"0"。 我已经调试了一段时间，但找不到为什么部分被重置，所以任何帮助将不胜感激！

Answer 1

您将上下文传递给您从未使用过的新创建的 ProjectsCDTVC 实例，并将立即解除分配。您需要将其传递给 segue.destinationViewController。

ProjectsCDTVC *pcdtvc = segue.destinationViewController;
[pcdtvc makeContext:self.context];