ios简单的图片缓存，

//简单的ios系统自带的图片缓存策略，
NSURL *url=[NSURL URLWithString:[NSString stringWithFormat:@"%@/%@",urlString,[texxImages objectAtIndex:i]]];
        //        [image setImageWithURL:url placeholderImage:nil];
        NSURLCache *urlCache = [NSURLCache sharedURLCache];
        /* 设置缓存的大小为1M*/
        [urlCache setMemoryCapacity:100*1024*1024];
        NSMutableURLRequest *request =[NSMutableURLRequest   requestWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:60.0f];
        //加载缓存策略
        NSCachedURLResponse *response=[urlCache cachedResponseForRequest:request];
        if (response!=Nil) {
            NSLog(@"如果有缓存输出，从缓存中获取数据");
            [request setCachePolicy:NSURLRequestReturnCacheDataDontLoad];
        }
        NSURLResponse *urlResponce=nil;
        NSError *error=nil;
        NSData *data=[NSURLConnection sendSynchronousRequest:request returningResponse:&urlResponce error:&error];
        UIImage *images=[UIImage imageWithData:data];

        image.frame = CGRectMake(weizhi, 0, images.size.width, images.size.height);
        image.image=images;
        weizhi = weizhi+images.size.width;
        image.backgroundColor=[UIColor clearColor];
        [scroll addSubview:image];

2 SDWebImage，第三方库，使用非常方便，导入库，

简单使用 [image setimage:url placeholderImage:image]

清除缓存的方法非常简单

 //清除所有缓存
    [[SDImageCache sharedImageCache] clearDisk];
    [[SDImageCache sharedImageCache] clearMemory];