iphone中的异步for循环

Question

for循环看起来像这样，我在视图中写的确实加载了，所以加载这个页面需要更多时间。

for (int i=3; i<[[[[dataDict objectForKey:@"rss"]objectForKey:@"channel"]objectForKey:@"item"]count]; i++)
{


    if (i%3==0)
    {
        x=0;
        y++;
    }

    view=[[UIView alloc]initWithFrame:CGRectMake((x*250)+5, (y*404)+6, 244, 400)];
    [view setBackgroundColor:[UIColor whiteColor]];
    view.layer.borderColor=[[UIColor whiteColor]CGColor];
    view.layer.borderWidth=1.0;
    view.layer.cornerRadius = 5;
    view.layer.masksToBounds = YES;
    [scroller addSubview:view];

titlelabel=[[UILabel alloc]initWithFrame:CGRectMake(10, 10, 230, 20)];
    [titlelabel setText:[[[[[[dataDict objectForKey:@"rss"]objectForKey:@"channel"]objectForKey:@"item"]objectAtIndex:i]objectForKey:@"title"]objectForKey:@"text"]];
    [titlelabel setNumberOfLines:0];
    titlelabel.font=[UIFont boldSystemFontOfSize:15.0f];




    [titlelabel setBackgroundColor:[UIColor clearColor]];
    [titlelabel sizeToFit];
    [view addSubview:titlelabel];

    datelabel=[[UILabel alloc]initWithFrame:CGRectMake(10, 62, 190, 20)];
    [datelabel setText:[[[[[[dataDict objectForKey:@"rss"]objectForKey:@"channel"]objectForKey:@"item"]objectAtIndex:i]objectForKey:@"title"]objectForKey:@"text"]];
    [datelabel setNumberOfLines:0];
    datelabel.font=[UIFont fontWithName:@"arial" size:12.0f];
    [datelabel setBackgroundColor:[UIColor clearColor]];
    [datelabel sizeToFit];
    [view addSubview:datelabel];

    NSData *data=[[NSData alloc]initWithContentsOfURL:[NSURL URLWithString:[[[[[[[dataDict objectForKey:@"rss"]objectForKey:@"channel"]objectForKey:@"item"]objectAtIndex:i]objectForKey:@"image"]objectForKey:@"text"]stringByAddingPercentEscapesUsingEncoding: NSUTF8StringEncoding]]];
    NSLog(@"data= %@",data);
    if (data==NULL ||[[[[[[[dataDict objectForKey:@"rss"]objectForKey:@"channel"]objectForKey:@"item"]objectAtIndex:i]objectForKey:@"image"]objectForKey:@"text"] isEqualToString:@""])
    {
        textview=[[UITextView alloc]initWithFrame:CGRectMake(2,80, 238, 386)];
        [textview setText:[[[[[[dataDict objectForKey:@"rss"]objectForKey:@"channel"]objectForKey:@"item"]objectAtIndex:i]objectForKey:@"title"]objectForKey:@"text"]];
        [textview setFont:[UIFont fontWithName:@"ArialMT" size:14]];
        [textview setDelegate:self];
        [view addSubview:textview];
    }
    else
    {
        imageview=[[UIImageView alloc]initWithFrame:CGRectMake(7, 80, 230, 150)];
        [imageview setImage:[UIImage imageWithData:data]];
        [view addSubview:imageview];

        textview=[[UITextView alloc]initWithFrame:CGRectMake(5, 240, 238, 200)];
        [textview setText:[[[[[[dataDict objectForKey:@"rss"]objectForKey:@"channel"]objectForKey:@"item"]objectAtIndex:i]objectForKey:@"title"]objectForKey:@"text"]];
        [textview setFont:[UIFont fontWithName:@"ArialMT" size:14]];
        [textview setDelegate:self];
        [view addSubview:textview];
    }

}

这里让我感到问题的是每次都从服务器获取的图像，所以这会变慢，请建议如何使它像延迟加载一样......

提前致谢

Answer 1

在我看来，UICollectionView 应该是显示此类数据的更好选择， 但它与ios5不兼容。

如果您需要 ios 5 兼容性，请查看该答案：https://stackoverflow.com/a/16039194/2707614

最后，为了回答你的问题，你可以尝试使用Grand Central Dispatch 如解释here

应该是这样的（我没有电脑可以测试）：

dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);

 dispatch_async(queue, ^{
for (int i=3; i<[[[self rssParser]rssItems]count]; i++)
    // for (int i=3; i<[titlearray count]; i++)
{
    if (i%3==0)
    {
        x=0;
        y++;
    }

    view=[[UIView alloc]initWithFrame:CGRectMake((x*250)+10, (y*306)+105, 244, 300)];
    [view setBackgroundColor:[UIColor whiteColor]];
    view.layer.borderColor=[[UIColor whiteColor]CGColor];
    view.layer.borderWidth=1.0;
    view.layer.cornerRadius = 5;
    view.layer.masksToBounds = YES;



    titlelabel=[[UILabel alloc]initWithFrame:CGRectMake(10, 10, 230, 20)];
    [titlelabel setText:[[[[self rssParser]rssItems]objectAtIndex:i-1]title]];
    [titlelabel setNumberOfLines:0];
    titlelabel.font=[UIFont boldSystemFontOfSize:14.0f];

    [titlelabel setBackgroundColor:[UIColor clearColor]];
    [titlelabel sizeToFit];


    datelabel=[[UILabel alloc]initWithFrame:CGRectMake(10, 62, 190, 20)];
    [datelabel setText:[[[[self rssParser]rssItems]objectAtIndex:i-1]pubDate]];
    [datelabel setNumberOfLines:0];
    datelabel.font=[UIFont fontWithName:@"arial" size:10.0f];
    [datelabel setBackgroundColor:[UIColor clearColor]];
    [datelabel sizeToFit];

    x++;

    dispatch_sync(dispatch_get_main_queue(), ^{
        [scroller addSubview:view];
        [view addSubview:titlelabel];
        [view addSubview:datelabel];
    });

}
});