Question

我是iOS编程的新手，所以希望有人可以帮助我...

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，它分隔到表视图控制器，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];

        }
    }
  }
}

该对象似乎正确地添加到数据表中，但是当我调用核心数据表视图控制器子类 ProjectsCDTVC 时，将永远不会调用cellForRowAtIndexPath。 ProjectsCDTVC 也被指定为故事板中表格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;
}

我看到一篇相关帖子指出，如果表格视图中的部分为零， cellForRowAtIndexPath 将不会被调用，所以我看了sections变量。部分最初具有正确的值＆＃39; 1＆＃39;但是，在某些时候，重置为＆＃39; 0＆＃39;。我已经调试了一段时间，无法找到为什么部分会被重置，所以任何帮助都会非常感激！

Answer 1

您将上下文传递给您从未使用的新创建的ProjectsCDTVC实例，并将立即取消分配。您需要将它传递给segue.destinationViewController。

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

表视图控制器中未显示数据表属性

1 个答案: