ios - 应用程序因 NSRangeException (NSMutableArray) 而终止

Question

我正在尝试从 Parse 检索上传的缩略图照片以在 UITableViewCells 中显示它们，但每次都会抛出异常。错误码如下:“Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSArrayM objectAtIndex:]: index 1 beyond bounds [0 .. 0]'”
这是我的代码:

- (void) viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];

PFQuery *query = [PFQuery queryWithClassName:@"Events"];
[query orderByDescending:@"date"];
[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
    if (error) {
        NSLog(@"Error: %@ %@", error, [error userInfo]);
    } else {
        self.events = (NSMutableArray *) objects;
        [self.tableView reloadData];

        for (PFObject *event in self.events) {

            NSInteger index = [self.events indexOfObject:event];

            PFFile *imageFile = [event objectForKey:@"thumbnailImage"];

            [imageFile getDataInBackgroundWithBlock:^(NSData *result, NSError *error) {

                if (error) {
                    //Handle Error
                } else {

                    UIImage *image = [UIImage imageWithData:result];

                    if (self.thumbnailPhotos == nil) {

                        self.thumbnailPhotos = [NSMutableArray array];
                        self.thumbnailPhotos[index] = image;
                    } else {

                    self.thumbnailPhotos[index] = image;
                    }

                    [self.tableView reloadData];
                }

            }];
        }
    }
}];

CellForRowAtIndexPath:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
static NSString *reuseIdentifier = @"Cell";
EventsTableViewCell *cell = (EventsTableViewCell *)[tableView dequeueReusableCellWithIdentifier:reuseIdentifier forIndexPath:indexPath];

PFObject *event = [self.events objectAtIndex:indexPath.row];

NSDate *date = [event objectForKey:@"date"];

NSString *dateString = [self.dateFormat stringFromDate:date];
NSString *timeString = [self.timeFormat stringFromDate:date];
NSLog(@"IndexPath.row = %ld", (long)indexPath.row);

if ([self.thumbnailPhotos objectAtIndex:indexPath.row] != nil) {

    cell.imageView.image = self.thumbnailPhotos[indexPath.row];
} else {
    NSLog(@"Nil, Application will crash!");
}

cell.eventNameLabel.text = [event objectForKey:@"title"];
cell.dateLabel.text = dateString;
cell.timeLabel.text = timeString;
[cell.timeLabel sizeToFit];

return cell;

}`

我必须添加 self.events 的索引值，因为缩略图照片的下载速度不同，所以我的单元格总是显示错误事件的错误照片。 我希望这是足够的细节来解决问题。

Answer 1

应用程序正在崩溃，因为 thumbnailPhotos 在索引处没有任何要分配的对象。请使用以下代码。

更新代码，支持字典保存缩略图

 /*

     Define events as NSMutableArray which holds all events 
     Define thumbnailPhotos as NSMutableDictionary which holds thumbnail image for index as key

     */

        //Create a weak Reference of self for accessing self within block

        __weak __typeof(self)weakSelf = self;
        PFQuery *query = [PFQuery queryWithClassName:@"Events"];
        [query orderByDescending:@"date"];
        [query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
            if (error) {
                NSLog(@"Error: %@ %@", error, [error userInfo]);
            } else {
                //Create a strong reference for updating the UI
                __strong __typeof(weakSelf)strongSelf = weakSelf;

                //Assign the events to instance object
                strongSelf.events = [NSMutableArray arrayWithArray:objects];

                //Alloced thumbnail dictionary
                strongSelf.thumbnailPhotos = [NSMutableDictionary dictionary];

                //Reload tableView so that data will be visible
                [strongSelf.tableView reloadData];

                for (PFObject *event in strongSelf.events) {

                    //Define index as block type because we have to use this instance within block
                   __block NSInteger index = [strongSelf.events indexOfObject:event];

                    PFFile *imageFile = [event objectForKey:@"thumbnailImage"];
                    [imageFile getDataInBackgroundWithBlock:^(NSData *result, NSError *error) {

                        if (error) {
                            //Handle Error
                        } else {

                            UIImage *image = [UIImage imageWithData:result];

                            //Set the image against index
                            [strongSelf.thumbnailPhotos setObject:@"" forKey:@(index)];

                            //Reload only cell for which image is just downloaded
                            [strongSelf.tableView reloadRowsAtIndexPaths:@[[NSIndexPath indexPathForRow:index inSection:0]] withRowAnimation:UITableViewRowAnimationAutomatic];
                        }

                    }];
                }
            }
        }];

更新: 修改你的 cellForRowAtIndexPath 如下

 - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    static NSString *reuseIdentifier = @"Cell";
    EventsTableViewCell *cell = (EventsTableViewCell *)[tableView dequeueReusableCellWithIdentifier:reuseIdentifier forIndexPath:indexPath];

    PFObject *event = [self.events objectAtIndex:indexPath.row];

    NSDate *date = [event objectForKey:@"date"];

    NSString *dateString = [self.dateFormat stringFromDate:date];
    NSString *timeString = [self.timeFormat stringFromDate:date];
    NSLog(@"IndexPath.row = %ld", (long)indexPath.row);

    if ([self.thumbnailPhotos valueForKey:@(indexPath.row)]) {

        cell.imageView.image = [self.thumbnailPhotos valueForKey:@(indexPath.row)];
    } else {
        NSLog(@"Nil, Application will crash!");
    }

    cell.eventNameLabel.text = [event objectForKey:@"title"];
    cell.dateLabel.text = dateString;
    cell.timeLabel.text = timeString;
    [cell.timeLabel sizeToFit];

    return cell;
}

在此实现中，缩略图图像被保存到字典中，并且 tableView 的第二次重新加载是基于每个单元格的，而不是重新加载完整的 tableView 来下载单个缩略图。