iOS开发

NSURLSession

iOS URL系统概述：

The URL loading system includes classes that load URLs along with a number of important helper classes that work with those URL loading classes to modify their behavior. The major helper classes fall into five categories: protocol support, authentication and credentials, cookie storage, configuration management, and cache management.（URL加载系统包括URL加载类和一些辅助类，这些辅助类完善URL加载类的操作）

1.URL支持的协议：
The URL loading system provides support for accessing resources using the following protocols:ftp:，http:，https:，data:，file:
It also transparently supports both proxy servers and SOCKS gateways using the user’s system preferences.
(URL：统一资源定位符(uniform resource locator)，是在网络中定位资源位置的表示方法.
组成：协议/服务器/路径/文件名；协议(schema)包括http,https,ftp,mail,file,telnet等)
URLloadsystem
2.URL加载类的区别

  • Using the NSURLSession class to asynchronously fetch the contents of a URL to memory or download files to disk in iOS 7 and later or OS X v10.9 and later
  • Using NSURLConnection to asynchronously fetch the contents of a URL to memory in older versions of iOS or OS X.
  • Using NSURLDownload to download files asynchronously to disk in older versions of OS X.

    NSURLSession

    1.NSURLSession Class

  • NSURLSession—A session object.
  • NSURLSessionConfiguration—A configuration object used when initializing the session.
  • NSURLSessionTask—The base class for tasks within a session.
  • : NSURLSessionDataTask—A task for retrieving the contents of a URL as an NSData object
  • :: NSURLSessionUploadTask—A task for uploading a file, then retrieving the contents of a URL as an NSData object
  • : NSURLSessionDownloadTask—A task for retrieving the contents of a URL as a temporary file on disk

    NSURLSession Protocol

  • NSURLSessionDelegate
  • :NSURLSessionTaskDelegate<NSURLSessionDelegate>
  • ::NSURLSessionDataDelegate<NSURLSessionTaskDelegate>
  • ::NSURLSessionDownloadDelegate<NSURLSessionTaskDelegate>

    2.Use NSURLSession

  • 1) Create a session configuration. 

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    [NSURLSessionConfiguration defaultSessionConfiguration]

  • 2) Create a session, specifying a configuration object and, optionally, a delegate.

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    sessionWithConfiguration:
    //根据创建的Configuration创建一个Session，系统默认创建一个新的OperationQueue处理Session的消息。
    sessionWithConfiguration:delegate:delegateQueue:
    //设定回调的delegate（这个delegate会被强引用），并设定delegate在哪个OperationQueue回调，如果设置为[NSOperationQueue mainQueue]就能在主线程进行回调非常的方便。

  • 3) Create task objects within a session that each represent a resource request

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    - (NSURLSessionDataTask *)dataTaskWithRequest:(NSURLRequest *)request;
    - (NSURLSessionDataTask *)dataTaskWithURL:(NSURL *)url;
    - (NSURLSessionDownloadTask *)downloadTaskWithURL:(NSURL *)url;
    - (NSURLSessionDownloadTask *)downloadTaskWithResumeData:(NSData *)resumeData;
    NSURLSessionDownloadTask *task = [NSURLSession  downloadTaskWithURL:url]

  • 4) Call its delegate methods. 

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    //NSURLSessionTaskDelegate 
    - (void)URLSession:task:didCompleteWithError:
    //NSURLSessionDataDelegate
    - (void)URLSession:dataTask:didReceiveResponse:completionHandler:
    - (void)URLSession:dataTask:didReceiveData:
    //NSURLSessionDownloadDelegate
    - (void)URLSession:downloadTask:didFinishDownloadingToURL:
    - (void)URLSession:downloadTask:didWriteData:totalBytesWritten:totalBytesExpectedToWrite:
    - (void)URLSession:downloadTask:didResumeAtOffset:expectedTotalBytes:

3.NSURLSession断点续传

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#import "ViewController.h"

@interface ViewController () <NSURLSessiondownloaddelegate,NSURLSessiondatadelegate>
@property (weak, nonatomic) IBOutlet UIProgressView *progressView;
- (IBAction)download:(UIButton *)sender;
@property (nonatomic, strong) NSURLSessionDownloadTask *task;
@property (nonatomic, strong) NSData *resumeData;
@property (nonatomic, strong) NSURLSession *session;
@end

@implementation ViewController
//懒加载
- (NSURLSession *)session
{
    if (!_session) {
        // 获得session
        NSURLSessionConfiguration *cfg = [NSURLSessionConfiguration defaultSessionConfiguration];
        self.session = [NSURLSession sessionWithConfiguration:cfg delegate:self delegateQueue:[NSOperationQueue mainQueue]];
    }
    return _session;
}
- (IBAction)download:(UIButton *)sender {
    // 按钮状态取反
    sender.selected = !sender.isSelected;
    if (self.task == nil) { 
        // 开始（继续）下载
        if (self.resumeData) { 
            // 恢复
            [self resume];
        } else { 
            // 开始
            [self start];
        }
    } else 
    { 
        // 暂停
        [self pause];
    }
}
/**
*  从零开始
*/
- (void)start
{
    // 1.创建一个下载任务
    NSURL *url = [NSURL URLWithString:@"http://192.168.1.110:8080/Server/resources"];
    self.task = [self.session downloadTaskWithURL:url];
    // 2.开始任务
    [self.task resume];
}
/**
*  恢复（继续）
*/
- (void)resume
{
    // 传入上次暂停下载返回的数据，就可以恢复下载
    self.task = [self.session downloadTaskWithResumeData:self.resumeData];

    // 开始任务
    [self.task resume];

    // 清空
    self.resumeData = nil;
}
/**
*  暂停
*/
- (void)pause
{
    __weak typeof(self) weakSelf = self;//弱引用，避免block内强引用循环
    [self.task cancelByProducingResumeData:^(NSData *resumeData) {
        //  resumeData : 包含了继续下载的开始位置\下载的url
        weakSelf.resumeData = resumeData;
        weakSelf.task = nil;
    }];
}
#pragma mark - NSURLSessionDownloadDelegate
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
didFinishDownloadingToURL:(NSURL *)location
{
    NSString *caches = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];
    // response.suggestedFilename ： 建议使用的文件名，一般跟服务器端的文件名一致
    NSString *file = [caches stringByAppendingPathComponent:downloadTask.response.suggestedFilename];

    // 将临时文件剪切或者复制Caches文件夹
    NSFileManager *mgr = [NSFileManager defaultManager];

    // AtPath : 剪切前的文件路径
    // ToPath : 剪切后的文件路径
    [mgr moveItemAtPath:location.path toPath:file error:nil];
}
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
didWriteData:(int64_t)bytesWritten
totalBytesWritten:(int64_t)totalBytesWritten
totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite
{
    NSLog(@"获得下载进度--%@", [NSThread currentThread]);
    // 获得下载进度
    self.progressView.progress = (double)totalBytesWritten / totalBytesExpectedToWrite;
}
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
didResumeAtOffset:(int64_t)fileOffset
expectedTotalBytes:(int64_t)expectedTotalBytes
{
}