如何实现延迟加载到uiscrollview答案

【问题标题】：How to implement lazy loading to uiscroll view如何实现延迟加载到uiscrollview
【发布时间】：2013-09-30 09:24:54
【问题描述】：

如何实现uiscroll视图的延迟加载

我正在从网络服务中获取 15 张图像并将其添加到 UIscrollview 我想用临时图像加载滚动视图，当图像准备好时，它可以将图像添加到 uiscrollview

-(void)loadthscroll:(NSMutableArray *)idarray:(NSMutableArray *)imgarray
{



/*************scroll for scroll in in theater******************/

scrollview_intheater= [[UIScrollView alloc] initWithFrame:CGRectMake(0, btn_thhead.frame.size.height,view_banner.frame.size.width, view_intheater.frame.size.height-btn_thhead.frame.size.height)];
[view_intheater addSubview:scrollview_intheater];

[scrollview_thcsoon removeFromSuperview];
adj=5;
currentx=5;
for(int i=0;i<[imgarray count];i++)

{

    btn_theater_ct = [UIButton buttonWithType:UIButtonTypeCustom];
    btn_theater_ct.frame=CGRectMake(currentx, 5, 95, 120);
    [btn_theater_ct addTarget:self action:@selector(theaterAction:) forControlEvents:UIControlEventTouchDown];
    [scrollview_intheater addSubview:btn_theater_ct];
    addr = [imgarray objectAtIndex:i];
    addr = [addr stringByAddingPercentEscapesUsingEncoding:NSASCIIStringEncoding];
    //NSLog(@"addr-------%@",addr);
    data_theater = [NSData dataWithContentsOfURL:[NSURL URLWithString:addr ] ];        
    [btn_theater_ct setBackgroundImage:[UIImage imageWithData:data_theater] forState:UIControlStateNormal];
    currentx +=btn_theater_ct.frame.size.width+adj;
    btn_theater_ct.tag=i;
    [scrollview_intheater setContentSize:CGSizeMake(currentx,0)];
    NSLog(@"add th scroll--%d----%d",[imgarray count],i);

}


}

【问题讨论】：

标签： iphone ios objective-c uiscrollview lazy-loading

【解决方案1】：

几天前我遇到了同样的问题，但我现在解决了导入

#import "UIImageView+AFNetworking.h"

并实现其方法

- (void)setImageWithURL:(NSURL *)url  placeholderImage:(UIImage *)placeholderImage;

要使用这个你必须使用 AFNetworking 类

【讨论】：

【解决方案2】：

使用loading image 设置整个 UIScrollView
创建一个交换给定图像并在需要时更新内容大小的方法
添加例程下载图片

现在您可以设置 UIScrollView 并调用例程进行下载。然后下载完成后调用方法交换图片就完成了。

【讨论】：

【解决方案3】：

尝试研究 GCD(GrandCentralDispatch) 并使用您的场景。可能这会适合你。

    -(void)loadthscroll:(NSMutableArray *)idarray:(NSMutableArray *)imgarray
    {

    scrollview_intheater= [[UIScrollView alloc] initWithFrame:CGRectMake(0, btn_thhead.frame.size.height,view_banner.frame.size.width, view_intheater.frame.size.height-btn_thhead.frame.size.height)];
    [view_intheater addSubview:scrollview_intheater];

    [scrollview_thcsoon removeFromSuperview];
    adj=5;
    currentx=5;


    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
//Here, do your iteration part like parsing URL from array and hitting the service which is background thread.            

            for(int i=0;i<[imgarray count];i++)
          {
                btn_theater_ct = [UIButton buttonWithType:UIButtonTypeCustom];
                btn_theater_ct.frame=CGRectMake(currentx, 5, 95, 120);
                [btn_theater_ct addTarget:self action:@selector(theaterAction:)                                                 forControlEvents:UIControlEventTouchDown];
                [scrollview_intheater addSubview:btn_theater_ct];

            currentx +=btn_theater_ct.frame.size.width+adj;
                [scrollview_intheater setContentSize:CGSizeMake(currentx,0)];

            NSLog(@"add th scroll--%d----%d",[imgarray count],i);
            addr = [imgarray objectAtIndex:i];
                addr = [addr stringByAddingPercentEscapesUsingEncoding:NSASCIIStringEncoding];
                //NSLog(@"addr-------%@",addr);
                data_theater = [NSData dataWithContentsOfURL:[NSURL URLWithString:addr ] ];   
            UIImage *receivedImage = [UIImage imageWithData:data_theater];
            }
                dispatch_async(dispatch_get_main_queue(), ^{

//Here, do your UI work like set the background image which is include in main thread                    

                    if([receivedImage isKindOfClass:[UIImage class]])
                    {
                        [btn_theater_ct setBackgroundImage: receivedImage];
                    btn_theater_ct.tag=i;
                    }
                });

        });

    }

【讨论】：