iOS NSURLSession的使用
一、代码块方法
// 数据信息下载
- (void)dataload
{
// 创建Data Task，用于打开我的csdn blog主页
NSURL *url = [NSURL URLWithString:@"http://h.hiphotos.baidu.com/image/pic/item/ac345982b2b7d0a2a3f98e71c9ef76094b369a2e.jpg"];
NSURLRequest *request = [NSURLRequest requestWithURL:url];
NSURLSession *session = [NSURLSession sharedSession];
NSURLSessionDataTask *dataTask = [session dataTaskWithRequest:request completionHandler: ^(NSData *data, NSURLResponse *response, NSError *error) {
// 输出返回的状态码，请求成功的话为200
NSHTTPURLResponse* httpResponse = (NSHTTPURLResponse *)response;
NSInteger responseStatusCode = [httpResponse statusCode];
NSLog(@"%ld", responseStatusCode);
UIImage *image = [UIImage imageWithData:data];
imageview.image = image;
}];
// 使用resume方法启动任务
[dataTask resume];
}
二、代理方法
1、定义标识符
static NSString *const kCurrentSession = @"Current Session";
static NSString *const kBackgroundSession = @"Background Session";
static NSString *const kBackgroundSessionID = @"cn.edu.scnu.DownloadTask.BackgroundSession";
2、属性定义
@property (strong, nonatomic) NSURLSession *currentSession; // 当前会话
@property (strong, nonatomic) NSURLSessionDownloadTask *cancellableTask; // 可取消的下载任务
3、创建实例
// 创建当前的session
- (void)createCurrentSession
{
NSURLSessionConfiguration *defaultConfig = [NSURLSessionConfiguration defaultSessionConfiguration];
self.currentSession = [NSURLSession sessionWithConfiguration:defaultConfig delegate:self delegateQueue:nil];
self.currentSession.sessionDescription = kCurrentSession;
}
// 创建可取消的下载任务
- (void)cancellableDownload:(id)sender
{
if (!self.cancellableTask)
{
if (!self.currentSession)
{
[self createCurrentSession];
}
NSString *imageURLStr = @"http://farm6.staticflickr.com/5505/9824098016_0e28a047c2_b_d.jpg";
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:imageURLStr]];
self.cancellableTask = [self.currentSession downloadTaskWithRequest:request];
[self setDownloadButtonsWithEnabled:NO];
self.downloadedImageView.image = nil;
[self.cancellableTask resume];
}
}
#pragma mark - NSURLSessionDownloadDelegate
// 无断点续传时的代理执行顺序：1-3-4；有断点续传时的代理执行顺序：2-1-3-4
// 执行下载任务时有数据写入
- (void)URLSession:(NSURLSession *)session
downloadTask:(NSURLSessionDownloadTask *)downloadTask
didWriteData:(int64_t)bytesWritten // 每次写入的data字节数
totalBytesWritten:(int64_t)totalBytesWritten // 当前一共写入的data字节数
totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite // 期望收到的所有data字节数
{
NSLog(@"1");
// 计算当前下载进度
double downloadProgress = totalBytesWritten / (double)totalBytesExpectedToWrite;
}
// 从fileOffset位移处恢复下载任务
- (void)URLSession:(NSURLSession *)session
downloadTask:(NSURLSessionDownloadTask *)downloadTask
didResumeAtOffset:(int64_t)fileOffset
expectedTotalBytes:(int64_t)expectedTotalBytes
{
NSLog(@"2");
}
// 完成下载任务，只有下载成功才调用该方法
- (void)URLSession:(NSURLSession *)session
downloadTask:(NSURLSessionDownloadTask *)downloadTask
didFinishDownloadingToURL:(NSURL *)location
{
NSLog(@"3");
// 取消已经完成的下载任务
if (downloadTask == self.cancellableTask)
{
self.cancellableTask = nil;
}
}
// 完成下载任务，无论下载成功还是失败都调用该方法
- (void)URLSession:(NSURLSession *)session
task:(NSURLSessionTask *)task
didCompleteWithError:(NSError *)error
{
NSLog(@"4");
if (error)
{
NSLog(@"下载失败：%@", error);
[self setDownloadProgress:0.0];
self.downloadedImageView.image = nil;
}
}