Ios 通过多个UIActivityIndicatorView正确使用Grand Central Dispatch

我正在创建一个由UIButtons组成的缩略图查看器，并希望在每个按钮中都有一个微调器，直到图像从云中填充。我以前用单纺纱机做过，但从来没有像这样大规模。微调器没有出现（可能是非主线程UI问题？）…我至少朝着正确的方向前进了吗？提前谢谢

dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0);
dispatch_queue_t queue2 = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0);
dispatch_apply(numberOfThumbs, queue, ^(size_t i){
    Post *post = [arrayOfPosts objectAtIndex:i];
    UIActivityIndicatorView *newSpinner = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
    UIButton *currentThumb = [[UIButton buttonWithType:UIButtonTypeCustom] retain];
    [currentThumb setFrame:CGRectMake((105.5 * (i%3))+3.5, ((i/3)*105.5) + 3.5, 102, 102)];
    [newSpinner setFrame:CGRectMake(54 - spinner.frame.size.width/2, 54 - spinner.frame.size.height/2, spinner.frame.size.width, spinner.frame.size.height)];
    [currentThumb addSubview:newSpinner];
    [newSpinner startAnimating];
    [thumbnails addObject:currentThumb];
    dispatch_async(queue2, ^(void){
        [currentThumb setImage:[UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:post.thumbUrl]]] forState:UIControlStateNormal];
        [newSpinner stopAnimating];
        [newSpinner removeFromSuperview];
        [newSpinner release];
    });
    [currentThumb release];
});
dispatch_release(queue);
dispatch_release(queue2);

多亏了丹尼尔和布拉德的建议，下面的舞蹈似乎奏效了：

    - (id)initWithArrayOfPosts:(NSArray*)posts
    {
        self = [super initWithNibName:nil bundle:nil];
        if (self) {
            // Custom initialization
            arrayOfPosts = [posts retain];
            numberOfThumbs = [arrayOfPosts count];
            oldDequeueFactor = 0;
            oldYOffset = 0.0;
            thumbnails = [[NSMutableArray alloc] initWithCapacity:15];
            mainScrollView = [[UIScrollView alloc] init];
            [mainScrollView setFrame:self.view.frame];
            [mainScrollView setContentSize:CGSizeMake(self.view.frame.size.width, 109 * (ceilf((float)numberOfThumbs/3.0)))];
            [mainScrollView setDelegate:self];
            [mainScrollView setBackgroundColor:[UIColor whiteColor]];
            [self setView:mainScrollView];

            for (int i=0; i<numberOfThumbs; i++) {
                UIActivityIndicatorView *newSpinner = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
                UIButton *currentThumb = [[UIButton buttonWithType:UIButtonTypeCustom] retain];
                [currentThumb setFrame:CGRectMake((105.5 * (i%3))+3.5, ((i/3)*105.5) + 3.5, 102, 102)];
                [newSpinner setFrame:CGRectMake(54 - newSpinner.frame.size.width/2, 54 - newSpinner.frame.size.height/2, newSpinner.frame.size.width, newSpinner.frame.size.height)];
                [currentThumb addSubview:newSpinner];
                [newSpinner startAnimating];
                [thumbnails addObject:currentThumb];
                [currentThumb release];
                [mainScrollView addSubview:[thumbnails objectAtIndex:i]];
                [self getImageDataAsynchronouslyForThumbnail:[thumbnails objectAtIndex:i] forIndex:i andRemoveSpinner:newSpinner];
            }
        }
        return self;
    }

    - (void)getImageDataAsynchronouslyForThumbnail:(UIButton*)thumb forIndex:(int)index andRemoveSpinner:(UIActivityIndicatorView *)spinner
{
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0);

    dispatch_async(queue, ^(void){
        Post *post = [arrayOfPosts objectAtIndex:index];
        UIImage *thisImage = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:post.thumbUrl]]];
        NSArray *args = [NSArray arrayWithObjects:thisImage, thumb, spinner, nil];
        if ([args count] == 3) { //use this array to verify I have all info I need
            dispatch_sync(dispatch_get_main_queue(), ^(void) {
                [self setImage:[args objectAtIndex:0] ForThumbnail:[args objectAtIndex:1] andStopAnimatingSpinner:[args objectAtIndex:2]];
            });
        } else {
            [self getImageDataAsynchronouslyForThumbnail:thumb forIndex:index andRemoveSpinner:spinner];
            return;
        }
    });

    dispatch_release(queue);

}

- (void)setImage:(UIImage*)image ForThumbnail:(UIButton *)thumb andStopAnimatingSpinner:(UIActivityIndicatorView *)spinner
{
    [thumb setImage:image forState:UIControlStateNormal];
    [spinner stopAnimating];
    [spinner removeFromSuperview];
    [spinner release];
}

-（id）initWithArrayOfPosts:（NSArray*）posts
{
self=[super initWithNibName:nil bundle:nil]；
如果（自我）{
//自定义初始化
arrayOfPosts=[保留职位]；
numberOfThumbs=[arrayOfPosts计数]；
oldDequeueFactor=0；
oldYOffset=0.0；
缩略图=[[NSMutableArray alloc]initWithCapacity:15]；
mainScrollView=[[UIScrollView alloc]init]；
[mainScrollView设置框架：self.view.frame]；
[mainScrollView setContentSize:CGSizeMake（self.view.frame.size.width，109*（celf（（float）numberOfThumbs/3.0））；
[mainScrollView setDelegate:self]；
[mainScrollView setBackgroundColor:[UIColor whiteColor]]；
[自设置视图：主滚动视图]；
对于（int i=0；i是的，我认为您的问题是您正在从后台线程执行代码，UIKit不是线程安全的，因此您可能应该只在后台获取图像数据，然后使用performSelectorOnMainTHread来设置图像并停止动画，例如

-(void)setDataStopAnimating:(NSArray*)args
{
   //get your arguments from the array and then run
 [thumb setImage:[UIImage imageWithData:imageData] forState:UIControlStateNormal];
                [newSpinner stopAnimating];
                [newSpinner removeFromSuperview];
                [newSpinner release];
}

//then in your queue code
      dispatch_async(queue2, ^(void){
               NSArray *args; //fill the array with the arguments
                [self performSelectorOnMainThread:@selector(setDataAndStopAnimating:) withObject:args] 
            });

如果有帮助的话，该代码似乎适用于设备上的一些缩略图，而不是模拟器上的缩略图。在您修订的代码中，我相信您可以将
-performSelectorInBackground:
替换为
dispatch\u async（dispatch\u get\u global\u queue（dispatch\u queue\u PRIORITY\u DEFAULT，0），^{}）
将所有内容保留在GCD内，避免为参数创建临时NSArray。哦，无论如何，这都应该执行SelectorInMainThread:withObject。让我修改一下，并尝试一些仅使用GCD的选项。谢谢。更新了Brad的建议，仅使用GCD进行线程。哦，好的。我会尝试一下。我从来没有混合过formSelector和GCD，谢谢。@diatrevolo我也没有试过，所以它可能不起作用，如果不起作用，那么您可以执行selectorOnBackground来获取数据，一定要让我们知道它是否起作用…UIImage*image=[UIImage imageWithData:imageData]是线程安全的，我认为。-它还缓存它，这可能不是期望的行为。除了
-performselectornmainthread:
，您可以使用GCD方式
dispatch\u sync（dispatch\u get\u main\u queue（），^{}）
（或者dispatch\u async，如果您不想阻止，直到主线程操作完成）。这避免了传入参数数组的需要。