ios - 数据表属性未出现在 TableView Controller 中

Question

我是 iOS 编程的新手，希望有人能帮助我...

我正在使用 TableView Controller 来显示使用数据模型创建的数据表中的内容。我有一个 View Controller，它连接到 Table View Controller，它首先创建上下文:

- (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];

        }
    }
  }
}

对象似乎已正确添加到数据表中，但当我调用 Core Data Table View Controller 子类 ProjectsCDTVC 时，cellForRowAtIndexPath 从未被调用。 ProjectsCDTVC 也被指定为 Storyboard 中 TableView Controller 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;
}

我看到一篇相关帖子指出，如果 TableView 中的节数 为零，则不会调用cellForRowAtIndexPath，因此我查看了节变量。部分最初的正确值为“1”，但在某些时候被重置为“0”。我已经调试了一段时间，无法找到部分重置的原因，因此非常感谢任何帮助!

Answer 1

您正在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];