滚动uitableview时解析后应用程序崩溃

Question

请查看我的代码。应用程序工作正常，但是当我快速向上或向下滚动时它就会崩溃。

* 由于未捕获的异常“NSRangeException”而终止应用程序，原因：“* -[__NSArrayM objectAtIndex:]：索引 0 超出范围 空数组'

这里是cellforrawatindexpath方法

- (UITableViewCell *)tableView:(UITableView *)myTableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

        UITableViewCell *cell = (UITableViewCell *)[self.messageList dequeueReusableCellWithIdentifier:@"ChatListItem"];
        if (cell == nil) {
            NSArray *nib;
            if ([[[rssOutputData objectAtIndex:indexPath.row] xml_userType] isEqualToString:@"2"])// THIS IS THE LINE WHERE IT CRASHES
 {
                nib = [[NSBundle mainBundle] loadNibNamed:@"OutGoing" owner:self options:nil];
                textLabel =[[UILabel alloc] initWithFrame:CGRectMake(58,12,241,30 )];

                cell.textLabel.textAlignment = NSTextAlignmentLeft;

            }else {
                nib = [[NSBundle mainBundle] loadNibNamed:@"InComing" owner:self options:nil];
                textLabel =[[UILabel alloc] initWithFrame:CGRectMake(21,12,241,30)];
                cell.textLabel.textAlignment = NSTextAlignmentRight;
            }
            cell = (UITableViewCell *)[nib objectAtIndex:0];
        }
        textLabel = (UILabel *)[cell viewWithTag:1];
        userLabel = (UILabel *)[cell viewWithTag:2];
        avatar = (UIImageView *)[cell viewWithTag:3];
        timeLabel = (UILabel *)[cell viewWithTag:4];

        NSString * test=[[rssOutputData objectAtIndex:indexPath.row]xml_msg];
        textLabel.text = test;
        textLabel.numberOfLines = 0; 
        [textLabel sizeToFit];
        [cell addSubview:textLabel];
        userLabel.text = [[rssOutputData objectAtIndex:indexPath.row]xml_username];

        avatar.layer.cornerRadius = 20.0;
        avatar.layer.masksToBounds = YES;
        if ([[[NSUserDefaults standardUserDefaults] stringForKey:@"patient_name"] isEqualToString:[[rssOutputData objectAtIndex:indexPath.row]xml_username]] || [[[NSUserDefaults standardUserDefaults] stringForKey:@"therapist"] isEqualToString:[[rssOutputData objectAtIndex:indexPath.row]xml_username]]) {
            avatar.image = [UIImage imageNamed:@"p.jpg"];
        }else {
            avatar.image = [UIImage imageNamed:@"t.jpg"];
        }
        rectTime = (CGRect){0, textLabel.frame.size.height+5, 241, 11};
        timeLabel = [[UILabel alloc] initWithFrame:rectTime];
        timeLabel.font = [UIFont systemFontOfSize:[UIFont smallSystemFontSize]];
        timeLabel.text = [[rssOutputData objectAtIndex:indexPath.row]xml_addedTime];
        timeLabel.backgroundColor = [UIColor clearColor];
        timeLabel.textColor = [UIColor lightGrayColor];
        [textLabel addSubview:timeLabel];

        return cell;
    }

实际上，我正在从每 5 秒调用一次的 xml 文件中加载数据。我将在这里发布我的解析代码。

- (void) Parse{
        previusCount = rssOutputData.count;
        rssOutputData = [[NSMutableArray alloc]init];
        NSString *post =[[NSString alloc] initWithFormat:@"https://messages_%@.xml",[[NSUserDefaults standardUserDefaults] stringForKey:@"xmls_id"]];
           dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH,0),^{

            NSData *xmlData=[[NSData alloc]initWithContentsOfURL:[NSURL URLWithString:post]];
            xmlParserObject =[[NSXMLParser alloc]initWithData:xmlData];
            [xmlParserObject setDelegate:self];
            [xmlParserObject parse];

            dispatch_async(dispatch_get_main_queue(), ^{
                [messageList reloadData];
            });
        });
}

这是来自 ViewDidLoad 的 NSTIMER

 timer = [NSTimer scheduledTimerWithTimeInterval:5.0 target: self selector: @selector(Parse) userInfo: nil repeats: YES];

下面是其余的解析代码

#pragma mark NSXMLParser delegate
//below delegate method is sent by a parser object to provide its delegate when it encounters a start tag
- (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qualifiedName attributes:(NSDictionary *)attributeDict
{
    if([elementName isEqualToString:@"message"]){
        xmlStringFileObject =[[XMLChatFile alloc]init];
    } else {
        nodecontent = [[NSMutableString alloc] init];
    }
}
- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string
{
    [nodecontent appendString:[string stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]]];
}
- (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName
{
    if([elementName isEqualToString:@"message"]){
        [rssOutputData addObject:xmlStringFileObject];
        xmlStringFileObject = nil;
    }
    else if([elementName isEqualToString:@"added"]){
        xmlStringFileObject.xml_addedTime= nodecontent;
        nodecontent = nil;
    }
    else if([elementName isEqualToString:@"user"]){
        xmlStringFileObject.xml_username= nodecontent;
        nodecontent = nil;
    }
    else if([elementName isEqualToString:@"text"]){
        xmlStringFileObject.xml_msg= nodecontent;
        nodecontent = nil;
    }
    else if([elementName isEqualToString:@"user_type"]){
        xmlStringFileObject.xml_userType= nodecontent;
        nodecontent = nil;
    }
}

Answer 1

是的，很明显，您正在尝试访问其中一个数组中不存在的元素。

问题：如果你在 Xcode 中“启用僵尸”然后重新运行你的代码，它会告诉你是哪一行导致了问题吗？

Enable zombies in Xcode

从那里，您应该能够找到原因。

您也可以尝试在 cellForRowAtIndexPath 函数的顶部粘贴这样的内容...

if (rssOutputData == nil)
    return;
if (rssOutputData.count <= objectAtIndex:indexPath.row)
    return;

...但我仍然认为这个问题是由您的 UITableView 尝试（快速）加载和显示数据引起的，而您的 5 秒函数正忙于清空然后刷新。

毕竟，每 5 秒 函数正在清空您的数组，然后等待 使用网络服务重新填充它。

在该网络服务完成之前，您的 UITableView 将绑定到其中没有数据的数据源...这不正常！！

    rssOutputData = [[NSMutableArray alloc]init];
    NSString *post =[[NSString alloc] initWithFormat:@"https://messages_%@.xml",
        [[NSUserDefaults standardUserDefaults] stringForKey:@"xmls_id"]];
   ... load data from this web service...

难怪滚动时它会崩溃......

顺便说一句，在您的 Parse 函数中，您在哪里将 rssOutputData 值设置为您刚刚从 Web 服务加载的任何内容...？

Answer 2

您的 rssOutputData 似乎为空或低于 numberOfRows。

看到你使用 rssOutputData，然后你重置它：

// ...
previusCount = rssOutputData.count;
rssOutputData = [[NSMutableArray alloc]init]; 
// ...

并且在您共享的代码中，您不会再次为其设置任何值。