#import "YYViewController.h"
#import "YYFileMultiDownloader.h"

@interface YYViewController ()
@property (nonatomic, strong) YYFileMultiDownloader *fileMultiDownloader;
@end

@implementation YYViewController
- (YYFileMultiDownloader *)fileMultiDownloader
{
  if (!_fileMultiDownloader) {
    _fileMultiDownloader = [[YYFileMultiDownloader alloc] init];
    // 需要下載的文件遠(yuǎn)程URL
    _fileMultiDownloader.url = @"http://192.168.1.200:8080/MJServer/resources/jre.zip";
    // 文件保存到什么地方
    NSString *caches = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];
    NSString *filepath = [caches stringByAppendingPathComponent:@"jre.zip"];
    _fileMultiDownloader.destPath = filepath;
  }
  return _fileMultiDownloader;
}

- (void)viewDidLoad
{
  [super viewDidLoad];
  
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
  [self.fileMultiDownloader start];
}

@end

#import <Foundation/Foundation.h>

@interface YYFileDownloader : NSObject
{
  BOOL _downloading;
}
/**
 * 所需要下載文件的遠(yuǎn)程URL(連接服務(wù)器的路徑)
 */
@property (nonatomic, copy) NSString *url;
/**
 * 文件的存儲路徑(文件下載到什么地方)
 */
@property (nonatomic, copy) NSString *destPath;

/**
 * 是否正在下載(有沒有在下載, 只有下載器內(nèi)部才知道)
 */
@property (nonatomic, readonly, getter = isDownloading) BOOL downloading;

/**
 * 用來監(jiān)聽下載進(jìn)度
 */
@property (nonatomic, copy) void (^progressHandler)(double progress);

/**
 * 開始(恢復(fù))下載
 */
- (void)start;

/**
 * 暫停下載
 */
- (void)pause;
@end

#import "YYFileDownloader.h"
 
@implementation YYFileDownloader
@end
下載器類繼承自YYFileDownloader這個類

YYFileSingDownloader.h文件
#import "YYFileDownloader.h"

@interface YYFileSingleDownloader : YYFileDownloader
/**
 * 開始的位置
 */
@property (nonatomic, assign) long long begin;
/**
 * 結(jié)束的位置
 */
@property (nonatomic, assign) long long end; 
@end
YYFileSingDownloader.m文件
#import "YYFileSingleDownloader.h"
@interface YYFileSingleDownloader() <NSURLConnectionDataDelegate>
/**
 * 連接對象
 */
@property (nonatomic, strong) NSURLConnection *conn;

/**
 * 寫數(shù)據(jù)的文件句柄
 */
@property (nonatomic, strong) NSFileHandle *writeHandle;
/**
 * 當(dāng)前已下載數(shù)據(jù)的長度
 */
@property (nonatomic, assign) long long currentLength;
@end

@implementation YYFileSingleDownloader

- (NSFileHandle *)writeHandle
{
  if (!_writeHandle) {
    _writeHandle = [NSFileHandle fileHandleForWritingAtPath:self.destPath];
  }
  return _writeHandle;
}

/**
 * 開始(恢復(fù))下載
 */
- (void)start
{
  NSURL *url = [NSURL URLWithString:self.url];
  // 默認(rèn)就是GET請求
  NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
  // 設(shè)置請求頭信息
  NSString *value = [NSString stringWithFormat:@"bytes=%lld-%lld", self.begin + self.currentLength, self.end];
  [request setValue:value forHTTPHeaderField:@"Range"];
  self.conn = [NSURLConnection connectionWithRequest:request delegate:self];
  
  _downloading = YES;
}

/**
 * 暫停下載
 */
- (void)pause
{
  [self.conn cancel];
  self.conn = nil;
  
  _downloading = NO;
}


#pragma mark - NSURLConnectionDataDelegate 代理方法
/**
 * 1. 當(dāng)接受到服務(wù)器的響應(yīng)(連通了服務(wù)器)就會調(diào)用
 */
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
  
}

/**
 * 2. 當(dāng)接受到服務(wù)器的數(shù)據(jù)就會調(diào)用(可能會被調(diào)用多次, 每次調(diào)用只會傳遞部分?jǐn)?shù)據(jù))
 */
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
  // 移動到文件的尾部
  [self.writeHandle seekToFileOffset:self.begin + self.currentLength];
  // 從當(dāng)前移動的位置(文件尾部)開始寫入數(shù)據(jù)
  [self.writeHandle writeData:data];
  
  // 累加長度
  self.currentLength += data.length;
  
  // 打印下載進(jìn)度
  double progress = (double)self.currentLength / (self.end - self.begin);
  if (self.progressHandler) {
    self.progressHandler(progress);
  }
}

/**
 * 3. 當(dāng)服務(wù)器的數(shù)據(jù)接受完畢后就會調(diào)用
 */
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
  // 清空屬性值
  self.currentLength = 0;
  
  // 關(guān)閉連接(不再輸入數(shù)據(jù)到文件中)
  [self.writeHandle closeFile];
  self.writeHandle = nil;
}

/**
 * 請求錯誤(失敗)的時候調(diào)用(請求超時\斷網(wǎng)\沒有網(wǎng), 一般指客戶端錯誤)
 */
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
  
}

@end

#import "YYFileDownloader.h"
@interface YYFileMultiDownloader : YYFileDownloader
@end

#import "YYFileMultiDownloader.h"
#import "YYFileSingleDownloader.h"

#define YYMaxDownloadCount 4

@interface YYFileMultiDownloader()
@property (nonatomic, strong) NSMutableArray *singleDownloaders;
@property (nonatomic, assign) long long totalLength;
@end

@implementation YYFileMultiDownloader

- (void)getFilesize
{
  NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:self.url]];
  request.HTTPMethod = @"HEAD";
  
  NSURLResponse *response = nil;
#warning 這里要用異步請求
  [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:nil];
  self.totalLength = response.expectedContentLength;
}

- (NSMutableArray *)singleDownloaders
{
  if (!_singleDownloaders) {
    _singleDownloaders = [NSMutableArray array];
    
    // 獲得文件大小
    [self getFilesize];
    
    // 每條路徑的下載量
    long long size = 0;
    if (self.totalLength % YYMaxDownloadCount == 0) {
      size = self.totalLength / YYMaxDownloadCount;
    } else {
      size = self.totalLength / YYMaxDownloadCount + 1;
    }
    
    // 創(chuàng)建N個下載器
    for (int i = 0; i<YYMaxDownloadCount; i++) {
      YYFileSingleDownloader *singleDownloader = [[YYFileSingleDownloader alloc] init];
      singleDownloader.url = self.url;
      singleDownloader.destPath = self.destPath;
      singleDownloader.begin = i * size;
      singleDownloader.end = singleDownloader.begin + size - 1;
      singleDownloader.progressHandler = ^(double progress){
        NSLog(@"%d --- %f", i, progress);
      };
      [_singleDownloaders addObject:singleDownloader];
    }
    
    // 創(chuàng)建一個跟服務(wù)器文件等大小的臨時文件
    [[NSFileManager defaultManager] createFileAtPath:self.destPath contents:nil attributes:nil];
    
    // 讓self.destPath文件的長度是self.totalLengt
    NSFileHandle *handle = [NSFileHandle fileHandleForWritingAtPath:self.destPath];
    [handle truncateFileAtOffset:self.totalLength];
  }
  return _singleDownloaders;
}

/**
 * 開始(恢復(fù))下載
 */
- (void)start
{
  [self.singleDownloaders makeObjectsPerformSelector:@selector(start)];
  
  _downloading = YES;
}

/**
 * 暫停下載
 */
- (void)pause
{
  [self.singleDownloaders makeObjectsPerformSelector:@selector(pause)];
  _downloading = NO;
}

@end