网络通信中关于请求数据、断点续传和写入本地文件

- (void)viewDidLoad {

    [super viewDidLoad];

    NSLog(@"%@",NSHomeDirectory());

    //取得已下载数据大小

    NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];

    receiveTotal = [[userDefaults objectForKey:@"ReceiveTotal"] doubleValue];

    total = [[userDefaults objectForKey:@"Total"] doubleValue];

    //显示上一次下载的进度

    if (total > 0) {

        CGFloat progress = receiveTotal/total;

        self.progressView.progress = progress;

        self.progressLabel.text = [NSString stringWithFormat:@"%.2f%%", progress * 100];

    }

}

- (IBAction)downLoadClick:(UIButton *)sender {

    if (!isDownLoad) {

        //1.构建URL

        NSURL *url = [NSURL URLWithString:@"http://s.qdcdn.com/lovebizhi/LoveWallpaper4Mac.dmg"];

        //2.构建Request

        NSMutableURLRequest *mRequest = [NSMutableURLRequest requestWithURL:url];

        //断点续传

        if (receiveTotal > 0) {

            //设置续传位置

            NSString *position = [NSString stringWithFormat:@"bytes=%d-",(int)receiveTotal];

            [mRequest setValue:position forHTTPHeaderField:@"Range"];

        }

        //3.发送异步请求

        connection = [NSURLConnection connectionWithRequest:mRequest delegate:self];

        isDownLoad = YES;

        //获取字符串

        NSString *urlStr = url.absoluteString;

        //获取urlStr的最后一部分

        NSString *fileName = [urlStr lastPathComponent];

        //写入文件

        filePath = [NSHomeDirectory() stringByAppendingFormat:@"/Documents/%@",fileName];

        //创建文件

        [[NSFileManager defaultManager] createFileAtPath:filePath contents:nil attributes:nil];

    }

}

//暂停下载

- (IBAction)pauseClick:(UIButton *)sender {

    //取消下载连接

    [connection cancel];

    connection = nil;

    //将缓冲数据写入文件

    [self appendFileData:self.receiveData];

    //在本地保存已下载文件的大小和文件总大小

    NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];

    [userDefaults setObject:@(receiveTotal) forKey:@"ReceiveTotal"];

    [userDefaults setObject:@(total) forKey:@"Total"];

    //将数据同步写入文件

    [userDefaults synchronize];

    isDownLoad = NO;

}

#pragma mark-NSURLConnectionDataDelegate

//服务器响应

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSHTTPURLResponse *)response{

    self.receiveData = [[NSMutableData alloc]init];

    //判断总大小是否为0，如果为0,说明从起始位置开始下，获取文件总大小

    if (total == 0) {

        //获取所有的响应头

        NSDictionary *fields = response.allHeaderFields;

        NSLog(@"fields is %@",fields);

        //获取数据的总大小

        NSNumber *length = [fields objectForKey:@"Content-Length"];

        total = [length doubleValue];

        NSLog(@"total is %.2f",total);

    }

}

//接收数据

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{

    [self.receiveData appendData:data];

    receiveTotal += data.length;

    //计算进度

    double progress = receiveTotal / total;

    //刷新UI

    self.progressView.progress = progress;

    self.progressLabel.text = [NSString stringWithFormat:@"%.2f%%",progress * 100];

    //判断缓冲的数据是否大于500KB

    if (self.receiveData.length >= 500 * 1024) {

        //写入数据

        [self appendFileData:self.receiveData];

        //清空

        self.receiveData.data = nil;

    }

}

//数据传输完成

- (void)connectionDidFinishLoading:(NSURLConnection *)connection{

    //将最后一个缓冲文件写入

    if (self.receiveData.length < 500 * 1024) {

        //写入数据

        [self appendFileData:self.receiveData];

        //清空

        self.receiveData.data = nil;

    }

    _progressLabel.text = @"下载完成";

    self.progressView.progress = 0;

    isDownLoad = NO;

}

- (void)appendFileData:(NSData *)data{

    if (data.length == 0) {

        return;

    }

    //使用NSFileHandle写文件，此文件必须已经创建，NSFileHandle不会创建文件

    NSFileHandle *fileHandle = [NSFileHandle fileHandleForWritingAtPath:filePath];

    //将数据插入到写入点

    [fileHandle seekToEndOfFile];

    [fileHandle writeData:data];

    //关闭文件，确保写入完成

    [fileHandle closeFile];

}

- (void)didReceiveMemoryWarning {

    [super didReceiveMemoryWarning];

    // Dispose of any resources that can be recreated.

}