iphone – 如何在使用线程时解决错误？

我在这里提交了示例代码

- (void)viewDidLoad {

    appDeleg = (NewAshley_MedisonAppDelegate *)[[UIApplication sharedApplication] delegate];
    [[self tblView1] setRowHeight:80.0];
    [super viewDidLoad];
    self.title = @"Under Ground";


    [UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
    [NSThread detachNewThreadSelector:@selector(CallParser) toTarget:self withObject:nil];

}

-(void)CallParser {


    Parsing *parsing = [[Parsing alloc] init];
    [parsing DownloadAndParseUnderground];

    [parsing release];
    [self Update_View];
    //[myIndicator stopAnimating];
    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;




}

这里的“DownloadAndParseUnderground”是从rss feed中下载数据的方法

-(void) Update_View{


    [self.tblView1 reloadData];
}

当调用Update_View方法时,tableView重载数据并在cellForRowAtIndexPath中创建错误而不显示自定义单元格

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


    static NSString *CellIdentifier = @"Cell";

    CustomTableviewCell *cell = (CustomTableviewCell *) [tblView1 dequeueReusableCellWithIdentifier:CellIdentifier];

    if (cell == nil) {

        [[NSBundle mainBundle] loadNibNamed:@"customCell"
                                      owner:self 
                                    options:nil];

        cell = objCustCell; 
        objCustCell = nil;

    }