# swoole_client->on 注册异步事件回调函数。 ```php int swoole_client::on(string $event, mixed $callback); ``` * 参数`1`为事件类型，支持`connect/error/receive/close` 4种 * 参数`2`为回调函数，可以是函数名字符串、匿名函数、类静态方法、对象方法。 * __同步阻塞客户端一定不要使用on方法__ > 调用`swoole_client->close()`时会自动退出事件循环 > `UDP`协议的`connect`事件在执行完`connect`方法后立即被回调 > `UDP`没有`close`事件 示例 ---- ```php $client = new swoole_client(SWOOLE_TCP | SWOOLE_ASYNC); //异步非阻塞 $client->on("connect", function($cli) { $cli->send("hello world\n"); }); $client->on("receive", function($cli, $data) { echo "received: $data\n"; sleep(1); $cli->send("hello\n"); }); $client->on("close", function($cli){ echo "closed\n"; }); $client->on("error", function($cli){ exit("error\n"); }); $client->connect('127.0.0.1', 9501, 0.5); ```