iOS网络之03文件下载

一，小文件下载：

1，NSData直接下载：（内部默认发送GET请求，但是只会在子线程，that‘s bad）

注意：这两种方法如果在下载过程中断网终止下载，那么重新下载需要从零开始，所以不适合大文件
不能监听下载进度

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    NSURL *url = [NSURL URLWithString:@"https://ss0.bdstatic.com/5aV1bjqh_Q23odCf/static/superman/img/logo/bd_logo1_31bdc765.png"];
    //下载到内存中
    NSData *data = [NSData dataWithContentsOfURL:url];
    NSLog(@"%lu",(unsigned long)data.length);
});

2，向服务器发送请求下载：（手动发送GET请求）

NSURL *url = [NSURL URLWithString:@"http://192.168.1.100:8080/MJServer/resources/images/minion_01.png"];
NSURLRequest *request = [NSURLRequest requestWithURL:url];

[NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse * _Nullable response, NSData * _Nullable data, NSError * _Nullable connectionError) {
    NSLog(@"%lu",data.length);
}];

二，单线程大文件下载：（可以监听下载进度）

1，非断点下载单线程下载，如下：

主要的API：（NSURLConnection异步方法，会自动开启异步线程，设置代理后可以通过代理方法监听事件并作出相应的处理）
[NSURLConnection connectionWithRequest:request delegate:self];

如下：

//1，发送请求
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
    NSURL *url = [NSURL URLWithString:@"http://w.x.baidu.com/alading/anquan_soft_down_all/14247"];
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    [NSURLConnection connectionWithRequest:request delegate:self];
}
//2，如果出错来到这里
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error{
    NSLog(@"didFailWithError");
}
//3，接受到响应，只会调用一次
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response{
    NSString *cachesPath = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];
    NSString *file = [cachesPath stringByAppendingPathComponent:@"QQ影音.exe"];
    
    NSFileManager *mgr = [NSFileManager defaultManager];
    [mgr createFileAtPath:file contents:nil attributes:nil];
    
    NSFileHandle *handle = [NSFileHandle fileHandleForWritingAtPath:file];
    self.handle = handle;
    self.totalLength = response.expectedContentLength;
}
//4，开始接受数据，调用多次，这里创建句柄对象对数据分段存储（如果只有一个子线程可以用下面seekToEndOfFile方法，如果是多线程那么需要先创建一个等同整个原始文件大小的文件，然后在用[self.handle seekToFileOffset:offset]方法存储数据）
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{
    [self.handle seekToEndOfFile];
    [self.handle writeData:data];
    self.currentLength += data.length;
    NSLog(@"下载进度是：%f",(double)self.currentLength/self.totalLength);
}
//5，存储完毕后关闭句柄，调用一次
- (void)connectionDidFinishLoading:(NSURLConnection *)connection{
    [self.handle closeFile];
    self.handle ＝ nil;
    self.currentLength = 0;
    self.totalLength = 0;
}

三，单线程的断点下载：

• 单线程断点下载.gif

- (IBAction)btnClicked:(UIButton *)sender {
    sender.selected = !sender.isSelected;
    
    if (sender.selected) {//下载或者重新下载
        //注意：这里的请求需要改成可变请求，因为后面要设置请求的下载位置
        NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:@"http://w.x.baidu.com/alading/anquan_soft_down_all/14247"]];
        //需要一个全局的request以方便我暂停之后重新下载的时候设置下载的位置
        self.request = request;
        
        //设置请求头，从当前位置下载
        NSString *range = [NSString stringWithFormat:@"bytes=%lld-",self.currentLength];
        [request setValue:range forHTTPHeaderField:@"Range"];
        
        //单线程下载（非断点下载）
        self.connection = [NSURLConnection connectionWithRequest:request delegate:self];
    }else{//按钮未被选中，暂停下载
        //NSURLConnection不支持暂停，只能取消，重新开始任务时候从当前位置下载等同于取消操作
        [self.connection cancel];
        self.connection = nil;
    }
}

//如果请求失败调用
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error{
    NSLog(@"didFailWithError---%@",error);
}

//建立连接获得相应的时候调用，只会调用一次,这里因为要实现断点续传，所以这个方法会调用多次，每次暂停一次就会重新调用一次
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response{
    NSLog(@"didReceiveResponse--接收到响应，开始下载--%@",response);
    //下面这句非常重要，如果没有这一句，会重新创建新的文件，会出问题
    if (self.currentLength) return;
    
    NSString *filePath = @"/users/feng/desktop/QQ影音.exe";
    NSFileManager *manager = [NSFileManager defaultManager];
    [manager createFileAtPath:filePath contents:nil attributes:nil];
    
    //建立句柄以方便后面每接受到一段数据可以插入到文件后面
    NSFileHandle *handle = [NSFileHandle fileHandleForWritingAtPath:filePath];
    self.handle = handle;
    //统计该数据的总大小
    self.totalLength = response.expectedContentLength;
}

//每次获取一段数据调用过一次，会调用多次
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{
    //    NSLog(@"didReceiveData----%@",data);
    NSLog(@"didReceiveData------");
    [self.handle seekToEndOfFile];
    [self.handle writeData:data];
    
    self.currentLength += data.length;
    self.progressView.progress = (double)self.currentLength/self.totalLength;
}

//完成下载的时候调用一次
- (void)connectionDidFinishLoading:(NSURLConnection *)connection{
    NSLog(@"connectionDidFinishLoading");
    
    [self.handle closeFile];
    self.handle = nil;
    
    self.totalLength = 0;
    self.currentLength = 0;
    self.btn.selected = NO;
}