ios - 只有最后一个 uitableview 单元格是正确的，其余显示空项目

Question

基本上我正在学习本教程:http://thedarkdev.blogspot.co.uk/2013/09/web-service-apps-in-ios7-json-with.html由于某种原因，最后一个单元格显示了正确的信息，但前面的单元格只显示标题:

此外，控制台窗口中的输出显示作者的信息信息。所以出于某种原因，它没有被拉入其他牢房。

这是 .m 文件:

#import "ViewController.h"

@interface ViewController ()
{
    NSMutableArray *myObject;
    // A dictionary object
    NSDictionary *dictionary;
    // Define keys
    NSString *title;
    NSString *thumbnail;
    NSString *author;
    NSString *permalink;
}
@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    title = @"title";
    thumbnail = @"thumbnail";
    author = @"author";
    permalink = @"permalink";

    myObject = [[NSMutableArray alloc] init];

    NSData *jsonSource = [NSData dataWithContentsOfURL:
                      [NSURL URLWithString:@"http://ios-blog.co.uk/?feed=json"]];

    id jsonObjects = [NSJSONSerialization JSONObjectWithData:
                  jsonSource options:NSJSONReadingMutableContainers error:nil];

    for (NSDictionary *dataDict in jsonObjects) {
        NSString *title_data = [dataDict objectForKey:@"title"];
        NSString *thumbnail_data = [dataDict objectForKey:@"thumbnail"];
        NSString *author_data = [dataDict objectForKey:@"author"];
        NSString *permalink_data = [dataDict objectForKey:@"permalink"];

        NSLog(@"TITLE: %@",title_data);
        NSLog(@"THUMBNAIL: %@",thumbnail_data);
        NSLog(@"AUTHOR: %@",author_data);
        NSLog(@"URL: %@",permalink_data);

        dictionary = [NSDictionary dictionaryWithObjectsAndKeys:
                  title_data, title,
                  thumbnail_data, thumbnail,
                  author_data,author,
                  permalink_data,permalink,
                  nil];
        [myObject addObject:dictionary];
    }
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section{
     return myObject.count;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{
    static NSString *CellIdentifier = @"Item";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

    if (cell == nil) {
        cell=[[UITableViewCell alloc]initWithStyle:
          UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier];
    }

    NSDictionary *tmpDict = [myObject objectAtIndex:indexPath.row];

    NSMutableString *text;
    //text = [NSString stringWithFormat:@"%@",[tmpDict objectForKey:title]];
    text = [NSMutableString stringWithFormat:@"%@",
            [tmpDict objectForKeyedSubscript:title]];

    NSMutableString *detail;
detail = [NSMutableString stringWithFormat:@"Author: %@ ",
          [tmpDict objectForKey:author]];

    NSMutableString *images;
    images = [NSMutableString stringWithFormat:@"%@ ",
              [tmpDict objectForKey:thumbnail]];

    NSURL *url = [NSURL URLWithString:[tmpDict objectForKey:thumbnail]];
    NSData *data = [NSData dataWithContentsOfURL:url];
    UIImage *img = [[UIImage alloc]initWithData:data];

    cell.textLabel.text = text;
    cell.detailTextLabel.text= detail;
    cell.imageView.frame = CGRectMake(0, 0, 80, 70);
    cell.imageView.image =img;

    return cell;

}

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    NSLog(@"URL: %@", [[myObject objectAtIndex:indexPath.row] objectForKey:permalink]);

    NSString* launchUrl = (@"%@", [[myObject objectAtIndex:indexPath.row] objectForKey:permalink]);
    [[UIApplication sharedApplication] openURL:[NSURL URLWithString: launchUrl]];
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

任何想法为什么以及如何解决这个问题？提前致谢:)

编辑:解决此解决方案后，感谢 Martin R 提供的答案:如果任何 dictionaryWithObjectsAndKeys 值为 nil，我如何提供默认值？

Answer 1

问题出在这里:

 NSDictionary *dictionary = [NSDictionary dictionaryWithObjectsAndKeys:
                          title_data, title,
                          thumbnail_data, thumbnail,
                          author_data,author,
                          permalink_data,permalink,
                          nil];

您的 JSON 数组中的许多对象没有“缩略图”条目，并且 thumbnail_data 为 nil。

但是 nil 充当 dictionaryWithObjectsAndKeys: 的终止符，因此，以下键“author”和“permalink”将被忽略。

有多种方法可以解决这个问题。例如，你可以使用 dictionaryWithValuesForKeys: 而不是 dictionaryWithObjectsAndKeys::

for (NSDictionary *dataDict in jsonObjects) {
    NSDictionary *dictionary = [dataDict dictionaryWithValuesForKeys:@[title, thumbnail, author, permalink]];
    [myObject addObject:dictionary];
}

此方法将 NSNull 值替换为 nil 值(并且代码更少)。

然后，在 cellForRowAtIndexPath 中，检查该值是否为 NSNull:

NSDictionary *tmpDict = dataDict[indexPath.row];
NSString *thumbnailURL = tmpDict[thumbnail];
UIImage *img;
if ([thumbnailURL isEqual:[NSNull null]]) {
    img = [UIImage imageNamed:@"DefaultImage.png"];
} else {
    NSURL *url = [NSURL URLWithString:[tmpDict objectForKey:thumbnail]];
    NSData *data = [NSData dataWithContentsOfURL:url];
    img = [[UIImage alloc] initWithData:data];
}