11. "Wanli" Raspberry Pi car - socket learning (sent from Android)

lb8820265 · Published on 2021-11-29 20:14

11. "Wanli" Raspberry Pi car - socket learning (sent from Android) [Copy link]

We have tested sockets on Windows and Linux. Now let's try using sockets on Android, using Windows as the server and the phone as the client, using the UDP communication protocol. The Windows code is as follows:

For the Android code, please refer to the introduction in " C Language Chinese Website ". The article uses the UDP protocol to send a string of characters per second, but only gives the core code, not the project. Beginners will fail if they are not careful. Let me create a new project from scratch step by step.

APP building steps

Create a new blank project using Android Studio.

Add network usage permissions in AndroidManifest.xml

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
<uses-permission android:name="android.permission.INTERNET"/>

Add a linear layout, a text box and a button to the layout file.

Add the button response callback function in MainActivity.java and start the thread in the callback function.

The thread function sends a string of characters to the specified IP address and port every second. The IP address in the code needs to obtain the IP address of the PC, and agree on a communication port, such as 1234, which needs to be consistent with the server code of the PC.

The full code is as follows.

package com.example.lb_socket_udp_simple;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
public class MainActivity extends AppCompatActivity {
private Button btn_listen;
private EditText et;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
et= (EditText) findViewById (R.id.edit_text);
btn_listen= (Button) findViewById (R.id.button);
btn_listen.setOnClickListener (new View.OnClickListener(){
@Override
public void onClick (View v) {
et.setText ("开始发送数据...");
new SendThread().start();
}
});
}
}
class SendThread extends Thread {
public void run(){
try {
//首先创建一个DatagramSocket 对象
DatagramSocket socket=new DatagramSocket(1235);
//创建一个InetAddree,自己测试的时候要设置成自己的IP地址
InetAddress serverAddress= InetAddress.getByName ("192.168.31.34");
while (true) {
String str="Hi, lb8820265!";
byte data []=str.getBytes ();
//创建一个DatagramPacket 对象，并指定要将这个数据包发送到网络当中的哪个地址以及端口号
DatagramPacket packet=new DatagramPacket(data,data.length,serverAddress,1234);
//调用socket 对象的send 方法，发送数据
socket.send (packet) ;
Log.d ("server", "sending...") ;
Thread.sleep (1000) ;
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}

How to run

Connect the mobile phone and PC to the same router, obtain the IP address of the PC, and modify the IP address in the APP code.
Compile and run the socket_UDP_win_server.cpp written previously on Windows.
Compile and run the app on your device, then click the "Send" button.

Operation Results

The received data will be continuously displayed in the Windows terminal