NSURLSession 实现下载功能

大神连接 包含离线下载功能

• viewDidLoad

- (void)viewDidLoad {
    [super viewDidLoad];
    
    _progressview = [[UIProgressView alloc] initWithProgressViewStyle:UIProgressViewStyleDefault];
    _progressview.frame = CGRectMake(20.0f, 100.0f, 200.0f, 30.0f);
    _progressview.trackTintColor = [UIColor grayColor];
    _progressview.progressTintColor = [UIColor orangeColor];
    [self.view addSubview:_progressview];
    
    NSURL *url = [NSURL URLWithString:@"http://dldir1.qq.com/qqfile/QQforMac/QQ_V5.4.0.dmg"];

    NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
    NSURLSession *session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:[NSOperationQueue mainQueue]];
    NSURLSessionDownloadTask *downloadTask = [session downloadTaskWithURL:url];
    [downloadTask resume];
}

• NSURLSessionDelegate

/**
 *  文件下载完毕时调用
 */
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
didFinishDownloadingToURL:(NSURL *)location
{
    // 文件将要移动到的指定目录
    NSString *documentsPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) firstObject];
    
    // 新文件路径
    NSString *newFilePath = [documentsPath stringByAppendingPathComponent:@"QQ_V5.4.0.dmg"];
    
    NSLog(@"File downloaded to: %@",newFilePath);
    
    // 移动文件到新路径
    [[NSFileManager defaultManager] moveItemAtPath:location.path toPath:newFilePath error:nil];
    
}

/**
 *  每次写入数据到临时文件时，就会调用一次这个方法。可在这里获得下载进度
 *
 *  @param bytesWritten              这次写入的文件大小
 *  @param totalBytesWritten         已经写入沙盒的文件大小
 *  @param totalBytesExpectedToWrite 文件总大小
 */
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
      didWriteData:(int64_t)bytesWritten
 totalBytesWritten:(int64_t)totalBytesWritten
totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite
{
    
    // 下载进度
    _progressview.progress = 1.0 * totalBytesWritten / totalBytesExpectedToWrite;
    NSLog(@"当前下载进度:%.2f%%",100.0 * totalBytesWritten / totalBytesExpectedToWrite);
}

/**
 *  恢复下载后调用
 */
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
 didResumeAtOffset:(int64_t)fileOffset
expectedTotalBytes:(int64_t)expectedTotalBytes
{
    NSLog(@"------");
}