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