@model類(lèi) 
#import <Foundation/Foundation.h> 
 
@interface NewsItem : NSObject 
 
@property (nonatomic,copy) NSString * newsTitle; 
@property (nonatomic,copy) NSString * newsPicUrl; 
@property (nonatomic,retain) UIImage * newsPic; //  存儲(chǔ)每個(gè)新聞自己的image對(duì)象 
 
- (id)initWithDictionary:(NSDictionary *)dic; 
 
//  處理解析 
+ (NSMutableArray *)handleData:(NSData *)data; 
@end 
 
 
#import "NewsItem.h" 
#import "ImageDownloader.h" 
 
@implementation NewsItem 
 
- (void)dealloc 
{ 
    self.newsTitle = nil; 
    self.newsPicUrl = nil; 
    self.newsPic = nil; 
    [super dealloc]; 
} 
 
- (id)initWithDictionary:(NSDictionary *)dic 
{ 
    self = [super init]; 
    if (self) { 
 
 
        self.newsTitle = [dic objectForKey:@"title"]; 
        self.newsPicUrl = [dic objectForKey:@"picUrl"]; 
         
        //從本地沙盒加載圖像 
        ImageDownloader * downloader = [[[ImageDownloader alloc] init] autorelease]; 
        self.newsPic = [downloader loadLocalImage:_newsPicUrl]; 
 
    } 
 
    return self; 
} 
 
+ (NSMutableArray *)handleData:(NSData *)data; 
{ 
 
        //解析數(shù)據(jù) 
        NSError * error = nil; 
        NSDictionary * dic = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:&error]; 
        NSMutableArray * originalArray = [dic objectForKey:@"news"]; 
 
        //封裝數(shù)據(jù)對(duì)象 
        NSMutableArray * resultArray = [NSMutableArray array]; 
     
        for (int i=0 ;i<[originalArray count]; i++) { 
            NSDictionary * newsDic = [originalArray objectAtIndex:i]; 
            NewsItem * item = [[NewsItem alloc] initWithDictionary:newsDic]; 
            [resultArray addObject:item]; 
            [item release]; 
        } 
 
        return resultArray; 
 
} 
 
@end 

@圖片下載類(lèi) 
#import <Foundation/Foundation.h> 
 
 
@class NewsItem; 
 
 
@interface ImageDownloader : NSObject 
 
 
@property (nonatomic,copy) NSString * imageUrl; 
@property (nonatomic,retain) NewsItem * newsItem; //下載圖像所屬的新聞 
 
 
//圖像下載完成后，使用block實(shí)現(xiàn)回調(diào) 
@property (nonatomic,copy) void (^completionHandler)(void); 
 
 
//開(kāi)始下載圖像 
- (void)startDownloadImage:(NSString *)imageUrl; 
 
 
//從本地加載圖像 
- (UIImage *)loadLocalImage:(NSString *)imageUrl; 
 
 
@end 
 
 
 
 
#import "ImageDownloader.h" 
#import "NewsItem.h" 
 
 
@implementation ImageDownloader 
 
 
- (void)dealloc 
{ 
    self.imageUrl = nil; 
    Block_release(_completionHandler); 
    [super dealloc]; 
} 
 
 
 
 
#pragma mark - 異步加載 
- (void)startDownloadImage:(NSString *)imageUrl 
{ 
 
 
    self.imageUrl = imageUrl; 
 
 
    // 先判斷本地沙盒是否已經(jīng)存在圖像，存在直接獲取，不存在再下載，下載后保存 
    // 存在沙盒的Caches的子文件夾DownloadImages中 
    UIImage * image = [self loadLocalImage:imageUrl]; 
 
 
    if (image == nil) { 
 
 
        // 沙盒中沒(méi)有，下載 
        // 異步下載,分配在程序進(jìn)程缺省產(chǎn)生的并發(fā)隊(duì)列 
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ 
 
 
            // 多線程中下載圖像 
            NSData * imageData = [NSData dataWithContentsOfURL:[NSURL URLWithString:imageUrl]]; 
 
 
            // 緩存圖片 
            [imageData writeToFile:[self imageFilePath:imageUrl] atomically:YES]; 
 
 
            // 回到主線程完成UI設(shè)置 
            dispatch_async(dispatch_get_main_queue(), ^{ 
 
 
                //將下載的圖像，存入newsItem對(duì)象中 
                UIImage * image = [UIImage imageWithData:imageData]; 
                self.newsItem.newsPic = image; 
 
 
                //使用block實(shí)現(xiàn)回調(diào)，通知圖像下載完成 
                if (_completionHandler) { 
                    _completionHandler(); 
                } 
                 
            }); 
             
        }); 
    } 
     
} 
 
#pragma mark - 加載本地圖像 
- (UIImage *)loadLocalImage:(NSString *)imageUrl 
{ 
 
    self.imageUrl = imageUrl; 
 
 
    // 獲取圖像路徑 
    NSString * filePath = [self imageFilePath:self.imageUrl]; 
 
 
    UIImage * image = [UIImage imageWithContentsOfFile:filePath]; 
 
 
    if (image != nil) { 
        return image; 
    } 
 
    return nil; 
} 
 
#pragma mark - 獲取圖像路徑 
- (NSString *)imageFilePath:(NSString *)imageUrl 
{ 
    // 獲取caches文件夾路徑 
    NSString * cachesPath = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject]; 
 
 
    // 創(chuàng)建DownloadImages文件夾 
    NSString * downloadImagesPath = [cachesPath stringByAppendingPathComponent:@"DownloadImages"]; 
    NSFileManager * fileManager = [NSFileManager defaultManager]; 
    if (![fileManager fileExistsAtPath:downloadImagesPath]) { 
 
 
        [fileManager createDirectoryAtPath:downloadImagesPath withIntermediateDirectories:YES attributes:nil error:nil]; 
    } 
 
 
#pragma mark 拼接圖像文件在沙盒中的路徑,因?yàn)閳D像URL有"/",要在存入前替換掉,隨意用"_"代替 
    NSString * imageName = [imageUrl stringByReplacingOccurrencesOfString:@"/" withString:@"_"]; 
    NSString * imageFilePath = [downloadImagesPath stringByAppendingPathComponent:imageName]; 
 
 
    return imageFilePath; 
} 
 
@end 

@這里只給出關(guān)鍵代碼,網(wǎng)絡(luò)請(qǐng)求,數(shù)據(jù)處理,自定義cell自行解決 
 
#pragma mark - Table view data source 
 
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView 
{ 
    // Return the number of sections. 
    return 1; 
} 
 
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section 
{ 
    // Return the number of rows in the section. 
    if (_dataArray.count == 0) { 
        return 10; 
    } 
    return [_dataArray count]; 
} 
 
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath 
{ 
    static NSString *cellIdentifier = @"Cell"; 
    NewsListCell *cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier ]; 
    if (!cell) { 
        cell = [[[NewsListCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifier] autorelease]; 
    } 
 
    NewsItem * item = [_dataArray objectAtIndex:indexPath.row]; 
 
    cell.titleLabel.text = item.newsTitle; 
 
    //判斷將要展示的新聞?dòng)袩o(wú)圖像 
 
    if (item.newsPic == nil) { 
        //沒(méi)有圖像下載 
        cell.picImageView.image = nil; 
         
        NSLog(@"dragging = %d,decelerating = %d",self.tableView.dragging,self.tableView.decelerating); 
        // ??執(zhí)行的時(shí)機(jī)與次數(shù)問(wèn)題 
        if (self.tableView.dragging == NO && self.tableView.decelerating == NO) { 
            [self startPicDownload:item forIndexPath:indexPath]; 
        } 
 
    }else{ 
        //有圖像直接展示 
        NSLog(@"1111"); 
        cell.picImageView.image = item.newsPic; 
 
    } 
     
    cell.titleLabel.text = [NSString stringWithFormat:@"indexPath.row = %ld",indexPath.row]; 
 
    return cell; 
} 
 
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath 
{ 
    return [NewsListCell cellHeight]; 
} 
 
//開(kāi)始下載圖像 
- (void)startPicDownload:(NewsItem *)item forIndexPath:(NSIndexPath *)indexPath 
{ 
    //創(chuàng)建圖像下載器 
    ImageDownloader * downloader = [[ImageDownloader alloc] init]; 
 
    //下載器要下載哪個(gè)新聞的圖像，下載完成后，新聞保存圖像 
    downloader.newsItem = item; 
 
    //傳入下載完成后的回調(diào)函數(shù) 
    [downloader setCompletionHandler:^{ 
 
        //下載完成后要執(zhí)行的回調(diào)部分，block的實(shí)現(xiàn) 
        //根據(jù)indexPath獲取cell對(duì)象，并加載圖像 
#pragma mark cellForRowAtIndexPath-->沒(méi)看到過(guò) 
        NewsListCell * cell = (NewsListCell *)[self.tableView cellForRowAtIndexPath:indexPath]; 
        cell.picImageView.image = downloader.newsItem.newsPic; 
 
    }]; 
 
    //開(kāi)始下載 
    [downloader startDownloadImage:item.newsPicUrl]; 
 
    [downloader release]; 
} 
 
 
- (void)loadImagesForOnscreenRows 
{ 
#pragma mark indexPathsForVisibleRows-->沒(méi)看到過(guò) 
    //獲取tableview正在window上顯示的cell，加載這些cell上圖像。通過(guò)indexPath可以獲取該行上需要展示的cell對(duì)象 
    NSArray * visibleCells = [self.tableView indexPathsForVisibleRows]; 
    for (NSIndexPath * indexPath in visibleCells) { 
        NewsItem * item = [_dataArray objectAtIndex:indexPath.row]; 
        if (item.newsPic == nil) { 
            //如果新聞還沒(méi)有下載圖像，開(kāi)始下載 
            [self startPicDownload:item forIndexPath:indexPath]; 
        } 
    } 
} 
 
#pragma mark - 延遲加載關(guān)鍵 
//tableView停止拖拽，停止?jié)L動(dòng) 
- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate 
{ 
    //如果tableview停止?jié)L動(dòng)，開(kāi)始加載圖像 
    if (!decelerate) { 
 
        [self loadImagesForOnscreenRows]; 
    } 
     NSLog(@"%s__%d__|%d",__FUNCTION__,__LINE__,decelerate); 
} 
 
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView 
{ 
    //如果tableview停止?jié)L動(dòng)，開(kāi)始加載圖像 
    [self loadImagesForOnscreenRows]; 
 
}

// 下拉刷新的原理 
- (void)scrollViewWillBeginDecelerating:(UIScrollView *)scrollView 
{ 
    if (scrollView.contentOffset.y < - 100) { 
         
        [UIView animateWithDuration:1.0 animations:^{ 
             
            //  frame發(fā)生偏移,距離頂部150的距離(可自行設(shè)定) 
            self.tableView.contentInset = UIEdgeInsetsMake(150.0f, 0.0f, 0.0f, 0.0f); 
        } completion:^(BOOL finished) { 
             
            /**
             *  發(fā)起網(wǎng)絡(luò)請(qǐng)求,請(qǐng)求刷新數(shù)據(jù)
             */ 
 
        }]; 
    } 
} 
 
// 上拉加載的原理 
- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate 
{ 
     
    NSLog(@"%f",scrollView.contentOffset.y); 
    NSLog(@"%f",scrollView.frame.size.height); 
    NSLog(@"%f",scrollView.contentSize.height); 
    /**
     *  關(guān)鍵-->
     *  scrollView一開(kāi)始并不存在偏移量,但是會(huì)設(shè)定contentSize的大小,所以contentSize.height永遠(yuǎn)都會(huì)比contentOffset.y高一個(gè)手機(jī)屏幕的
     *  高度;上拉加載的效果就是每次滑動(dòng)到底部時(shí),再往上拉的時(shí)候請(qǐng)求更多,那個(gè)時(shí)候產(chǎn)生的偏移量,就能讓contentOffset.y + 手機(jī)屏幕尺寸高大于這
     *  個(gè)滾動(dòng)視圖的contentSize.height
     */ 
    if (scrollView.contentOffset.y + scrollView.frame.size.height >= scrollView.contentSize.height) { 
         
        NSLog(@"%d %s",__LINE__,__FUNCTION__); 
        [UIView commitAnimations]; 
         
        [UIView animateWithDuration:1.0 animations:^{ 
            //  frame發(fā)生的偏移量,距離底部往上提高60(可自行設(shè)定) 
            self.tableView.contentInset = UIEdgeInsetsMake(0, 0, 60, 0); 
        } completion:^(BOOL finished) { 
             
            /**
             *  發(fā)起網(wǎng)絡(luò)請(qǐng)求,請(qǐng)求加載更多數(shù)據(jù)
             *  然后在數(shù)據(jù)請(qǐng)求回來(lái)的時(shí)候,將contentInset改為(0,0,0,0)
             */ 
        }]; 
 
    } 
}