ios - Objective-c Json 解析空数组错误或 Bug？

Question

当我用 tableview 解析 json 时，如果有 json 项，一切都很好，但如果没有加载 json 项，当我单击后退按钮时，会出现此错误。

erminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSArrayM objectAtIndex:]: index 0 beyond bounds for empty array'
*** First throw call stack:

我认为当我快速单击后退按钮时 json 不会加载，并在我的 TableView 代码下给出此错误。

    @interface MasterViewController ()

    @property (nonatomic, assign) NSInteger currentPage;
    @property (nonatomic, assign) NSInteger totalPages;
    @property (nonatomic, assign) NSInteger totalItems;
    @property (nonatomic, assign) NSInteger maxPages;

    @property (nonatomic, strong) NSMutableArray *activePhotos;
    @property (strong, nonatomic) NSMutableArray *staticDataSource;
    @property (nonatomic, strong) NSMutableArray *searchResults;

    @property (strong, nonatomic) IBOutlet UITableView *tableView;


    @end


            - (void)viewDidLoad
            {
                [super viewDidLoad];

                self.activePhotos = [[NSMutableArray alloc] init];
                self.searchResults = [[NSMutableArray alloc] init];
                self.staticDataSource = [[NSMutableArray alloc] init];


            }


            #pragma mark - Table View

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {

    return  self.activePhotos.count;
}



- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    UITableViewCell *cell;
    if (indexPath.row == [self.activePhotos count]) {
        cell = [self.tableView dequeueReusableCellWithIdentifier:@"LoadingCell" forIndexPath:indexPath];
        UIActivityIndicatorView *activityIndicator = (UIActivityIndicatorView *)[cell.contentView viewWithTag:100];
        [activityIndicator startAnimating];
    } else {
        NSDictionary *photoItem = self.activePhotos[indexPath.row];
        cell = [self.tableView dequeueReusableCellWithIdentifier:@"Cell" forIndexPath:indexPath];

        cell.textLabel.text = [photoItem objectForKey:@"name"];
        if (![[photoItem objectForKey:@"description"] isEqual:[NSNull null]]) {
            cell.detailTextLabel.text = [photoItem objectForKey:@"description"];
        }


    }


    return cell;
}



- (void)loadPhotos:(NSInteger)page
{



    NSString *userismim =[[NSUserDefaults standardUserDefaults] stringForKey:@"userisim"];


    NSArray* words = [userismim componentsSeparatedByCharactersInSet :[NSCharacterSet whitespaceAndNewlineCharacterSet]];
    NSString* nospacestring = [words componentsJoinedByString:@""];


    NSLog(@"%@",nospacestring);


    NSString *apiURL = [NSString stringWithFormat:@"http://bla.com/server/table.php?user=%@",nospacestring];

    NSURLSession *session = [NSURLSession sharedSession];
    [[session dataTaskWithURL:[NSURL URLWithString:apiURL]
            completionHandler:^(NSData *data,
                                NSURLResponse *response,
                                NSError *error) {

                if (!error) {

                    NSError *jsonError = nil;
                    NSMutableDictionary *jsonObject = (NSMutableDictionary *)[NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:&jsonError];

                    NSLog(@"%@",jsonObject);

                    [self.staticDataSource addObjectsFromArray:[jsonObject objectForKey:@"photos"]];

                    self.currentPage = [[jsonObject objectForKey:@"current_page"] integerValue];
                    self.totalPages  = [[jsonObject objectForKey:@"total_pages"] integerValue];
                    self.totalItems  = [[jsonObject objectForKey:@"total_items"] integerValue];

                    self.activePhotos = self.staticDataSource;

                    dispatch_async(dispatch_get_main_queue(), ^{
                        [self.tableView reloadData];
                    });
                }
            }] resume];
}

谢谢你所做的一切。我需要你的帮助。

Answer 1

您正在显示事件指示器，它将一直旋转直到 json 加载。

如果您在 json 加载之前按下后退按钮，应用会尝试分配空引用给数组，这是不可能的，因此它会抛出错误。

为避免这种情况，您可以在请求发出后停止 userInteraction，并仅在获得成功或失败响应后才启用。

要禁用交互，添加

[[UIApplication sharedApplicaton] beginIgnoringInteractionEvents]  

之后

NSURLSession *session = [NSURLSession sharedSession];

要再次启用，请添加:

 [[UIApplication sharedApplicaton] endIgnoringInteractionEvents]  

之前

if (!error) {

我希望这会解决您的问题。