iOS开发网络篇—实现大文件的多线程断点下载

YYFileMultiDownloader.m文件

#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 这里要用异步请求
  [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:nil];
  self.totalLength = response.expectedContentLength;
}

- (NSMutableArray *)singleDownloaders
{
  if (!_singleDownloaders) {
    _singleDownloaders = [NSMutableArray array];
    
    // 获得文件大小
    [self getFilesize];
    
    // 每条路径的下载量
    long long size = 0;
    if (self.totalLength % YYMaxDownloadCount == 0) {
      size = self.totalLength / YYMaxDownloadCount;
    } else {
      size = self.totalLength / YYMaxDownloadCount + 1;
    }
    
    // 创建N个下载器
    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];
    }
    
    // 创建一个跟服务器文件等大小的临时文件
    [[NSFileManager defaultManager] createFileAtPath:self.destPath contents:nil attributes:nil];
    
    // 让self.destPath文件的长度是self.totalLengt
    NSFileHandle *handle = [NSFileHandle fileHandleForWritingAtPath:self.destPath];
    [handle truncateFileAtOffset:self.totalLength];
  }
  return _singleDownloaders;
}

/**
 * 开始(恢复)下载
 */
- (void)start
{
  [self.singleDownloaders makeObjectsPerformSelector:@selector(start)];
  
  _downloading = YES;
}

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

@end