包括四個會話

• 簡單會話-通過NSURLSession靜態方法+sharedSession獲得NSURLSession對象

NSString *strURL = [[NSString alloc] initWithFormat:@"http://xxx/WebService.php?email=%@&type=%@&action=%@", @"xxx@xxx.com", @"JSON", @"query"];

    strURL = [strURL stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet URLQueryAllowedCharacterSet]];//將字符串轉化成URL字符串,例如"<"的URL編碼是"%3C"

    NSURL *url = [NSURL URLWithString:strURL];
    NSURLRequest *request = [[NSURLRequest alloc] initWithURL:url];

    NSURLSession *session = [NSURLSession sharedSession];
    NSURLSessionDataTask *task = [session dataTaskWithRequest:request completionHandler:
        ^(NSData *data, NSURLResponse *response, NSError *error) {
        NSLog(@"请求完成...");
        if (!error) {
            NSDictionary *resDict = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingAllowFragments error:nil];
            dispatch_async(dispatch_get_main_queue(), ^{
                [self reloadView:resDict];
            });
        } else {
            NSLog(@"error : %@", error.localizedDescription);
        }
    }];

    [task resume];

• 默認會話(default session)-通過NSURLSession靜態方法+sessionWithConfiguration:或者+sessionWithConfiguration:delegate:delegateQueue:獲得NSURLSession對象
  1,以下為GET方法請求數據

NSURLSessionConfiguration *defaultConfig = [NSURLSessionConfiguration defaultSessionConfiguration];
    NSURLSession *session = [NSURLSession sessionWithConfiguration: defaultConfig delegate: nil delegateQueue: [NSOperationQueue mainQueue]];

2,以下是POST請求,GET請求是NSURLRequest,POST請求是NSMutableURLRequest

    NSString *strURL = @"http://xxx/WebService.php";

    NSURL *url = [NSURL URLWithString:strURL];

    NSString *post = [NSString stringWithFormat:@"email=%@&type=%@&action=%@", @"xxx@xxx.com", @"JSON", @"query"];
    NSData *postData = [post dataUsingEncoding:NSUTF8StringEncoding];

    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    [request setHTTPMethod:@"POST"];
    [request setHTTPBody:postData];

    NSURLSessionConfiguration *defaultConfig = [NSURLSessionConfiguration defaultSessionConfiguration];
    NSURLSession *session = [NSURLSession sessionWithConfiguration: defaultConfig delegate: nil delegateQueue: [NSOperationQueue mainQueue]];

    NSURLSessionDataTask *task = [session dataTaskWithRequest:request completionHandler:
        ^(NSData *data, NSURLResponse *response, NSError *error) {
        NSLog(@"请求完成...");
        if (!error) {
            NSDictionary *resDict = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingAllowFragments error:nil];
            [self reloadView:resDict];
        } else {
            NSLog(@"error : %@", error.localizedDescription);
        }
    }];

    [task resume];

3,下載圖片

- (IBAction)onClick:(id)sender {

    NSString *strURL = [[NSString alloc] initWithFormat:@"http://xxx/download.php?email=%@&FileName=test1.jpg", @"xxx@xxx.com"];

    NSURL *url = [NSURL URLWithString:strURL];

    NSURLSessionConfiguration *defaultConfig = [NSURLSessionConfiguration defaultSessionConfiguration];
    NSURLSession *session = [NSURLSession sessionWithConfiguration:defaultConfig delegate:self delegateQueue:[NSOperationQueue mainQueue]];

    NSURLSessionDownloadTask *downloadTask = [session downloadTaskWithURL:url];

    [downloadTask resume];

}

#pragma mark -- 实现NSURLSessionDownloadDelegate委托协议
//下載中的方法,可以用來改變下載進度條
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite {
    
    float progress = totalBytesWritten * 1.0 / totalBytesExpectedToWrite;
    [self.progressView setProgress:progress animated:TRUE];
    NSLog(@"进度= %f", progress);
    NSLog(@"接收: %lld 字节 (已下载: %lld 字节)  期待: %lld 字节.", bytesWritten, totalBytesWritten, totalBytesExpectedToWrite);
}

//下載完成後調用的方法
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location {

    NSLog(@"临时文件: %@\n", location);

    NSString *downloadsDir = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, TRUE) objectAtIndex:0];

    NSString *downloadStrPath = [downloadsDir stringByAppendingPathComponent:@"test1.jpg"];
    NSURL *downloadURLPath = [NSURL fileURLWithPath:downloadStrPath];

    NSFileManager *fileManager = [NSFileManager defaultManager];

    NSError *error = nil;
    if ([fileManager fileExistsAtPath:downloadStrPath]) {
        [fileManager removeItemAtPath:downloadStrPath error:&error];
        if (error) {
            NSLog(@"删除文件失败: %@", error.localizedDescription);
        }
    }

    error = nil;

    if ([fileManager moveItemAtURL:location toURL:downloadURLPath error:&error]) {
        NSLog(@"文件保存: %@", downloadStrPath);
        UIImage *img = [UIImage imageWithContentsOfFile:downloadStrPath];
        self.imageView1.image = img;
        
    } else {
        NSLog(@"保存文件失败: %@", error.localizedDescription);
    }
}

• 短暫會話(ephemeral session)-通過NSURLSessionConfiguration靜態方法+ephemeralSessionConfiguration獲得
• 後臺會話(background session)-通過NSURLSessionConfiguration靜態方法+backgroundSessionConfigurationWithIdentifier:獲得

包括三種形式的任務

• 數據任務(data task) NSURLSessionDataTask類
• 上傳任務(upload task) NSURLSessionUploadTask類
• 下載任務(download task) NSURLSessionDownloadTask類