UIActivityIndi​​cator在重新加载新数据时没有显示UITableView

Question

我的基本问题是我似乎无法弄清楚如何将活动指示器置于顶部，这样我就可以在新数据填充UITableView时显示进程正在运行。要加载新数据，我使用的是分段控件。当按下段0时，它将加载第一个xml进给，当按下段1时，它将加载第二个xml进给。我已经尝试过使用dispatch_queue_t等。它会加载信息并重新填充表格，它只是没有显示指标。

这是我目前使用的代码。

if (Seg.selectedSegmentIndex == 0) {
    timer = [NSTimer scheduledTimerWithTimeInterval:(1.0/2.0) target:self selector:@selector(loading) userInfo:nil repeats:YES];

    dispatch_queue_t loader = dispatch_queue_create("a", NULL);
    dispatch_async(loader, ^{

        xml = [[XmlParser alloc]init];
        url = [NSURL URLWithString:kTodaysReport];
        dict = [[NSMutableDictionary alloc]init];
        [xml loadXML:url];
        [tableView addSubview:ActInd];
        dispatch_async(dispatch_get_main_queue(), ^{
        [[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(handleUpdate:) name:@"update" object:nil];

        });
    });



}
else if (Seg.selectedSegmentIndex ==1){
   // tableView = [[UITableView alloc]init];


    timer = [NSTimer scheduledTimerWithTimeInterval:(1.0/2.0) target:self selector:@selector(loading) userInfo:nil repeats:YES];

    dispatch_queue_t loader = dispatch_queue_create("a", NULL);
    dispatch_async(loader, ^{

        xml = [[XmlParser alloc]init];
        url = [NSURL URLWithString:kMonthsReport];
        dict = [[NSMutableDictionary alloc]init];
        [xml loadXML:url];
        [tableView addSubview:ActInd];
        dispatch_async(dispatch_get_main_queue(), ^{
            [[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(handleUpdate:) name:@"update" object:nil];
        });
    });
}

提前致谢。

编辑：相关代码

- (void)viewDidLoad
{
[super viewDidLoad];

dispatch_queue_t loader = dispatch_queue_create("a", NULL);
timer = [NSTimer scheduledTimerWithTimeInterval:(1.0/2.0) target:self selector:@selector(loading)     userInfo:nil repeats:YES];


    dispatch_async(loader, ^{


    xml = [[XmlParser alloc]init];
    url = [NSURL URLWithString:kTodaysReport];
    dict = [[NSMutableDictionary alloc]init];
    [xml loadXML:url];
    [UiTableView addSubview:ActInd];
    dispatch_async(dispatch_get_main_queue(), ^{
        [[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(handleUpdate:)     name:@"update" object:nil];
        [ActInd stopAnimating];
        [UiTableView reloadData];
    });
    });

}

-(void)handleUpdate:(NSNotification*)notification{
mainArray = [xml parsedArray];
[UiTableView reloadData];
}

-(void)loading{
if (![xml val]) {
    [ActInd startAnimating];
}else
{
    [ActInd stopAnimating];
    [UiTableView reloadData];
}
}
-(IBAction)segvalueChange:(id)sender{

if (Seg.selectedSegmentIndex == 0) {
    timer = [NSTimer scheduledTimerWithTimeInterval:(1.0/2.0) target:self selector:@selector(loading) userInfo:nil repeats:YES];

    dispatch_queue_t loader = dispatch_queue_create("a", NULL);
    dispatch_async(loader, ^{

        xml = [[XmlParser alloc]init];
        url = [NSURL URLWithString:kTodaysReport];
        dict = [[NSMutableDictionary alloc]init];
        [xml loadXML:url];
        [UiTableView addSubview:ActInd];
        dispatch_async(dispatch_get_main_queue(), ^{
        [[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(handleUpdate:) name:@"update" object:nil];

        });
    });



}
else if (Seg.selectedSegmentIndex ==1){
   // UiTableView = [[UITableView alloc]init];


    timer = [NSTimer scheduledTimerWithTimeInterval:(1.0/2.0) target:self     selector:@selector(loading) userInfo:nil repeats:YES];

    dispatch_queue_t loader = dispatch_queue_create("a", NULL);
    dispatch_async(loader, ^{

        xml = [[XmlParser alloc]init];
        url = [NSURL URLWithString:kMonthsReport];
        dict = [[NSMutableDictionary alloc]init];
        [xml loadXML:url];
        [UiTableView addSubview:ActInd];
        dispatch_async(dispatch_get_main_queue(), ^{
            [[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(handleUpdate:) name:@"update" object:nil];
        });
    });
}
else{
}
}

Answer 1

问题是您在后台线程上与UI进行交互。将所有与UI相关的代码（包括与活动视图交互的代码）移动到主线程的GCD块中。