iOS 断点续传-下载篇

获取本地文件大小

+ (long long)fileSize:(NSString *)filePath {
    
    
    if (![self fileExists:filePath]) {
    
    
        return 0;
    }
    NSDictionary *fileInfo = [[NSFileManager defaultManager]attributesOfItemAtPath:filePath error:nil];
    return [fileInfo[NSFileSize]longLongValue];
}

从已有大小处开始下载

- (void)downLoadWithURL:(NSURL *)url offset:(long long)offset {
    
    

    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url cachePolicy:NSURLRequestReloadIgnoringLocalCacheData timeoutInterval:0];
    [request setValue:[NSString stringWithFormat:@"bytes=%lld-",offset] forHTTPHeaderField:@"Range"];
    // session 分配的task,默认挂起状态
    self.dataTask = [self.session dataTaskWithRequest:request];
    [self resumeCurrentTask];
    
}

调用

    // 获取本地大小
    _tmpSize = [FFileTool fileSize:self.downLoadingrPath];
    // 获取文件的总大小(需要从网络上获得资源的大小)
    [self downLoadWithURL:url offset:_tmpSize];
    

-(NSURLSession *)session {
    
    
    if (!_session) {
    
    
        NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];
        _session = [NSURLSession sessionWithConfiguration:config delegate:self delegateQueue:[NSOperationQueue mainQueue]];
    }
    return _session;
}


// 继续任务
- (void)resumeCurrentTask {
    
    
    if (self.dataTask && self.state == FDownLoadStatePause) {
    
    
        [self.dataTask resume];
        self.state = FDownLoadStateDownLoading;
    }
}