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iOS开发之断点续传NSURLSessionDataTask

iOS开发之断点续传NSURLSessionDataTask

作者: chasitu | 来源:发表于2021-09-29 19:01 被阅读0次

    我们平时实际开发中文件下载一般都用AFNetworking比较多,刚开始学习iOS开发的时候用过,很多年没有使用过了,之前有的那点印象已经模糊的不能再模糊了,我们今天简单回顾一下,回到那个羞涩的秋天,

    思路(相关源码网上有很多,我这里重点是思路和容易犯错的点)

    1. 我们再iOS开发中使用网络请求一般都是使用NSURLSession类,实际使用中使用它的子类:NSURLSessionDataTaskNSURLSessionUploadTaskNSURLSessionDownloadTask,第一个就是我们今天要使用的类

    2. 创建NSURLSessionDataTask对象,然后调用它的resume方法之后网络请求就发送成功了,代理里面接受NSData数据就可以了(不能直接使用alloc来创建,切记)

    NSURLSessionDataTask *task = [session dataTaskWithRequest:mutiRequest];
        [task resume];
    
    1. 上面需要一个NSURLSession对象,我们就创建这个类
    NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration defaultSessionConfiguration];
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    NSURLSession *session = [NSURLSession sessionWithConfiguration:sessionConfiguration delegate:self delegateQueue:queue];
    
    • delegate这个默认是NSURLSessionDelegate,但是我们不能使用这个,需要子类的代理回调NSURLSessionTaskDelegate,相关代码我放下面哈
    • NSURLSessionConfiguration类是相关设置,正常是使用默认,还有两个选择,感兴趣的可以看看,有个后台模式应该有应用的场景
    1. 接下来就是那个请求类NSMutableURLRequest
    NSMutableURLRequest *mutiRequest = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:@"https://www.apple.com/105/media/cn/iphone-x/2017/01df5b43-28e4-4848-bf20-490c34a926a7/films/feature/iphone-x-feature-cn-20170912_1280x720h.mp4"]];
    NSString *range = [NSString stringWithFormat:@"bytes=%f-",self.currentLength];
    [mutiRequest setValue:range forHTTPHeaderField:@"Range"];
    
    • 这里必须使用可变请求类,因为可变请求类才有设置下载文件的范围
    • @"bytes=%f-"这个位置,byte后面是有s,我刚开始看别人的demo没有写s调试的时候一直出错,加了就好了,这个也是我今天想写这篇文章的主要原因
    • @"Range"这里是固定值

    delegate回调

    1. 回调1:返回一个响应头,block回调告知是否允许下载
    - (void)URLSession:(NSURLSession *)session dataTask:(nonnull NSURLSessionDataTask *)dataTask didReceiveResponse:(nonnull NSURLResponse *)response completionHandler:(nonnull void (^)(NSURLSessionResponseDisposition))completionHandler
    {
        NSLog(@"----开始----%lld---%@",response.expectedContentLength,response.MIMEType);
        self.totalLength = response.expectedContentLength+self.currentLength;
        // 允许处理服务器的响应,才会继续接收服务器返回的数据
        if (self.currentLength < self.totalLength) {
            completionHandler(NSURLSessionResponseAllow);
        }else{
            completionHandler(NSURLSessionResponseCancel);
        }
    }
    
    • response.expectedContentLength剩余下载量,我们上面传了已经下载的文件大小,这里会返回剩余文件的大小
    • completionHandler这个block回调应该不用多解释了哈
    1. 调用2:接受数据,写入数据,因为我们使用的是新建的队列,所以这里是子线程,更新UI操作需要回到主线程
    - (void)URLSession:(NSURLSession *)session dataTask:(nonnull NSURLSessionDataTask *)dataTask didReceiveData:(nonnull NSData *)data{
        [self.fileHandle writeData:data];
        dispatch_async(dispatch_get_main_queue(), ^{
            self.progressLabel.text = [NSString stringWithFormat:@"%.2f%%",100.0*dataTask.countOfBytesReceived/dataTask.countOfBytesExpectedToReceive];
        });
    }
    
    • 温馨提示这个方法调用的频率很高,不要把一些计算量较大的代码写在这里
    1. 回调3:任务结束,无错误
    - (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error
    {
        if (error == nil) {
            NSLog(@"----下载完成-----%@",error);
        }
    //    if (task.state == NSURLSessionTaskStateCompleted) {
    //        NSURLSessionTaskStateRunning = 0,
    //        NSURLSessionTaskStateSuspended = 1,
    //        NSURLSessionTaskStateCanceling = 2,
    //        NSURLSessionTaskStateCompleted = 3,
    //    }
    }
    

    全部代码

    @interface ViewController ()<NSURLSessionTaskDelegate>
    @property (nonatomic , strong) NSFileHandle *fileHandle;
    @property (nonatomic , strong) NSURLSessionDataTask *dataTask;
    @property (nonatomic , strong) UILabel *progressLabel;
    @property (nonatomic , copy) NSString *path;
    @end
    
    @implementation ViewController
    
    - (void)viewDidLoad {
        [super viewDidLoad];
        self.view.backgroundColor = UIColor.redColor;
        _progressLabel = [[UILabel alloc] initWithFrame:CGRectMake(0,0, self.view.bounds.size.width, 50)];
        _progressLabel.center = self.view.center;
        _progressLabel.backgroundColor = UIColor.lightGrayColor;
        _progressLabel.textAlignment = NSTextAlignmentCenter;
        _progressLabel.text = @"0.00%";
        [self.view addSubview:_progressLabel];
    }
    - (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
    {
        if (_dataTask) {
            [_dataTask cancel];
            _dataTask = nil;
        }else{
            self.currentLength = [[[NSFileManager defaultManager] attributesOfItemAtPath:self.path error:nil] fileSize];
            NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration defaultSessionConfiguration];
            NSOperationQueue *queue = [[NSOperationQueue alloc] init];
            NSURLSession *session = [NSURLSession sessionWithConfiguration:sessionConfiguration delegate:self delegateQueue:queue];
            NSMutableURLRequest *mutiRequest = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:@"https://www.apple.com/105/media/cn/iphone-x/2017/01df5b43-28e4-4848-bf20-490c34a926a7/films/feature/iphone-x-feature-cn-20170912_1280x720h.mp4"]];
            NSString *range = [NSString stringWithFormat:@"bytes=%f-",self.currentLength];
            [mutiRequest setValue:range forHTTPHeaderField:@"Range"];
            NSURLSessionDataTask *task = [session dataTaskWithRequest:mutiRequest];
            [task resume];
            _dataTask = task;
        }
    }
    - (void)URLSession:(NSURLSession *)session dataTask:(nonnull NSURLSessionDataTask *)dataTask didReceiveResponse:(nonnull NSURLResponse *)response completionHandler:(nonnull void (^)(NSURLSessionResponseDisposition))completionHandler
    {
        NSLog(@"----开始----%lld---%@",response.expectedContentLength,response.MIMEType);
        self.totalLength = response.expectedContentLength+self.currentLength;
        // 允许处理服务器的响应,才会继续接收服务器返回的数据
        completionHandler(NSURLSessionResponseAllow);
        //completionHandler(NSURLSessionResponseCancel);
    }
    - (void)URLSession:(NSURLSession *)session dataTask:(nonnull NSURLSessionDataTask *)dataTask didReceiveData:(nonnull NSData *)data{
        [self.fileHandle writeData:data];
        dispatch_async(dispatch_get_main_queue(), ^{
            self.progressLabel.text = [NSString stringWithFormat:@"%.2f%%",100.0*dataTask.countOfBytesReceived/dataTask.countOfBytesExpectedToReceive];
        });
    }
    - (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error
    {
        if (error == nil) {
            NSLog(@"----下载完成-----%@",error);
        }
    //    if (task.state == NSURLSessionTaskStateCompleted) {
    //        NSURLSessionTaskStateRunning = 0,
    //        NSURLSessionTaskStateSuspended = 1,
    //        NSURLSessionTaskStateCanceling = 2,
    //        NSURLSessionTaskStateCompleted = 3,
    //    }
    }
    - (NSFileHandle *)fileHandle
    {
        if (!_fileHandle) {
            NSFileManager *fm = [NSFileManager defaultManager];
            if (![fm fileExistsAtPath:self.path]) {
                [fm createFileAtPath:self.path contents:nil attributes:nil];
            }
            _fileHandle = [NSFileHandle fileHandleForWritingAtPath:self.path];
            [_fileHandle seekToEndOfFile];
        }
        return _fileHandle;
    }
    - (NSString *)path
    {
        if (!_path) {
            _path = [NSString stringWithFormat:@"/Users/XXXXXXX/Desktop/hahaha/iphone%u.mp4",arc4random()%9999];
        }
        return _path;
    }
    

    简单的一个断点续传,感兴趣的小伙伴可以把全部代码直接copy过去,修改一下保存文件的路径就可以运行

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