iOS NSURLSessionDownloadTask实现文件断点下载的方法

#import "ViewController.h"

@interface ViewController ()<NSURLSessionDownloadDelegate>
@property (nonatomic, strong) NSURLSessionDownloadTask *downloadTask;
@property (nonatomic, strong) NSData *resumData;
@property (nonatomic, strong) NSURLSession *session;
@end

@implementation ViewController

// 开始下载
- (IBAction)startBtnClick:(id)sender
{
  //1.url
  NSURL *url = [NSURL URLWithString:@"http://120.25.226.186:32812/resources/videos/minion_01.mp4"];
  
  //2.创建请求对象
  NSURLRequest *request = [NSURLRequest requestWithURL:url];
  
  //3.创建session
  NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];
  self.session = [NSURLSession sessionWithConfiguration:config delegate:self delegateQueue:[NSOperationQueue mainQueue]];
  
  //4.创建Task
  NSURLSessionDownloadTask *downloadTask = [self.session downloadTaskWithRequest:request];
  
  //5.执行Task
  [downloadTask resume];
  
  self.downloadTask = downloadTask;

}

//暂停是可以恢复
- (IBAction)suspendBtnClick:(id)sender
{
  NSLog(@"+++++++++++++++++++暂停");
  [self.downloadTask suspend];
}

//cancel:取消是不能恢复
//cancelByProducingResumeData:是可以恢复
- (IBAction)cancelBtnClick:(id)sender
{
  NSLog(@"+++++++++++++++++++取消");
  //[self.downloadTask cancel];
  
  //恢复下载的数据!=文件数据，也就是记录开始下载的位置的相关信息，倘若是已下载的文件数据，就会存在内存增大的问题
  [self.downloadTask cancelByProducingResumeData:^(NSData * _Nullable resumeData) {
    self.resumData = resumeData;
  }];
}

- (IBAction)goOnBtnClick:(id)sender
{
  NSLog(@"+++++++++++++++++++恢复下载");
  if(self.resumData)
  {
    self.downloadTask = [self.session downloadTaskWithResumeData:self.resumData];
  }
  
  [self.downloadTask resume];
}

#pragma mark ----------------------
#pragma mark NSURLSessionDownloadDelegate
/**
 * 写数据
 *
 * @param session          会话对象
 * @param downloadTask       下载任务
 * @param bytesWritten       本次写入的数据大小
 * @param totalBytesWritten     下载的数据总大小
 * @param totalBytesExpectedToWrite 文件的总大小
 */
-(void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite
{
  //1. 获得文件的下载进度
  NSLog(@"%f",1.0 * totalBytesWritten/totalBytesExpectedToWrite);
}

/**
 * 当恢复下载的时候调用该方法
 *
 * @param fileOffset     从什么地方下载
 * @param expectedTotalBytes 文件的总大小
 */
-(void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didResumeAtOffset:(int64_t)fileOffset expectedTotalBytes:(int64_t)expectedTotalBytes
{
  NSLog(@"%s",__func__);
}

/**
 * 当下载完成的时候调用
 *
 * @param location   文件的临时存储路径
 */
-(void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location
{
  NSLog(@"%@",location);
  
  //1 拼接文件全路径
  NSString *fullPath = [[NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:downloadTask.response.suggestedFilename];
  
  //2 剪切文件
  [[NSFileManager defaultManager]moveItemAtURL:location toURL:[NSURL fileURLWithPath:fullPath] error:nil];
  NSLog(@"%@",fullPath);
}

/**
 * 请求结束
 */
-(void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error
{
  NSLog(@"didCompleteWithError");
}

@end