Question

我有一个基本的相册应用程序，在第一个视图中会显示一个相册列表，其中的副标题显示每个相册中有多少个图像。我有一切都在努力添加相册，并将图像添加到相册。问题是每当应用程序加载时图像计数行都是准确的，但我无法在执行期间让它们更新。

以下viewdidload在应用加载时正确填充了tableview的所有行：

- (void)viewDidLoad {
    [super viewDidLoad]; 
    // Set the title.
    self.title = @"Photo albums";

    // Configure the add and edit buttons.
    self.navigationItem.leftBarButtonItem = self.editButtonItem;

    addButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self action:@selector(addAlbum)];
    addButton.enabled = YES;
    self.navigationItem.rightBarButtonItem = addButton;

    /*
    Fetch existing albums.
    Create a fetch request; find the Album entity and assign it to the request; add a sort descriptor; then execute the fetch.
    */
    NSFetchRequest *request = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Album" inManagedObjectContext:managedObjectContext];
    [request setEntity:entity];

    // Order the albums by name.
    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"albumName" ascending:NO];
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
    [request setSortDescriptors:sortDescriptors];
    [sortDescriptor release];
    [sortDescriptors release];

    // Execute the fetch -- create a mutable copy of the result.
    NSError *error = nil;
    NSMutableArray *mutableFetchResults = [[managedObjectContext executeFetchRequest:request error:&error] mutableCopy];
    if (mutableFetchResults == nil) {
        // Handle the error.
    }

    LocationsAppDelegate *mainDelegate = (LocationsAppDelegate *)[[UIApplication sharedApplication] delegate];

    // Set master albums array to the mutable array, then clean up.
    [mainDelegate setAlbumsArray:mutableFetchResults];
    [mutableFetchResults release];
    [request release];
}

但是当我在viewdidappear中运行类似的代码时，没有任何反应：

{
    /*
    Fetch existing albums.
    Create a fetch request; find the Album entity and assign it to the request; add a sort descriptor; then execute the fetch.
    */
    NSFetchRequest *request = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Album" inManagedObjectContext:managedObjectContext];
    [request setEntity:entity];

    // Order the albums by creation date, most recent first.
    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"albumName" ascending:NO];
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
    [request setSortDescriptors:sortDescriptors];
    [sortDescriptor release];
    [sortDescriptors release];

    // Execute the fetch -- create a mutable copy of the result.
    NSError *error = nil;
    NSMutableArray *mutableFetchResults = [[managedObjectContext executeFetchRequest:request error:&error] mutableCopy];
    if (mutableFetchResults == nil) {
        // Handle the error.
    }

    LocationsAppDelegate *mainDelegate = (LocationsAppDelegate *)[[UIApplication sharedApplication] delegate];

    // Set master albums array to the mutable array, then clean up.
    [mainDelegate setAlbumsArray:mutableFetchResults];
    [self.tableView reloadData];
    [mutableFetchResults release];
    [request release];  
}

道歉，如果我在其他地方错过了这个问题的答案，但我错过了什么？

Answer 1

要进行问题排查，请将NSLog语句放在-viewDidAppear:的几个位置。您可以使用这些日志语句来确保正确调用此方法并至少检查mutableFetchResults的内容。

数据未从次要更新的核心数据重新加载到tableview中

1 个答案: