Handler的基本用法

1. Handler 的Send message ,可以传： what , arg1 ,arg2 ,obj :

   
   

2. package com.example.userrecyclerviewapplication;
   
   import androidx.annotation.NonNull;
   import androidx.appcompat.app.AppCompatActivity;
   
   
   
   import android.os.Bundle;
   import android.os.Handler;
   import android.os.Message;
   import android.view.View;
   import android.widget.Button;
   import android.widget.TextView;
   import android.widget.Toast;
   
   
   import java.io.ByteArrayOutputStream;
   import java.io.IOException;
   import java.io.InputStream;
   import java.net.HttpURLConnection;
   import java.net.MalformedURLException;
   import java.net.ProtocolException;
   import java.net.URL;
   import java.util.List;
   import java.util.Random;
   
   
   import okhttp3.OkHttpClient;
   import okhttp3.Request;
   import okhttp3.Response;
   
   public class MainActivity extends AppCompatActivity {
       private Button send, upload;
       private TextView txt;
       private String str = "";
       private Handler handler = new Handler() {
           @Override
           public void handleMessage(@NonNull Message msg) {
               super.handleMessage(msg);
               if(msg.what == 1){
                   txt.setText(str);
               }else if(msg.what == 2){
                   String str2 = "What : "+ msg.what+";arg1:"+msg.arg1+";arg2:"+msg.arg2+";obj:"+((Random)msg.obj).nextInt();
                   txt.setText(str2);
               }
           }
       };
   
   
       @Override
       protected void onCreate(Bundle savedInstanceState) {
           super.onCreate(savedInstanceState);
           setContentView(R.layout.activity_main);
           initView();
           initEvent();
   
       }
   
   
       private void initView() {
           send = findViewById(R.id.send_request);
           upload = findViewById(R.id.upload);
           txt = findViewById(R.id.txt);
   
   
       }
   
       private void initEvent() {
           upload.setOnClickListener(new View.OnClickListener() {
               @Override
               public void onClick(View v) {
                   new Thread(new Runnable() {
                       @Override
                       public void run() {
                           Message message = new Message();
                           message.what = 2;
                           message.arg1 = 111;
                           message.arg2 = 222;
                           message.obj = new Random();
                           handler.sendMessage(message);
                       }
                   }){}.start();
               }
           });
           send.setOnClickListener(new View.OnClickListener() {
               @Override
               public void onClick(View v) {
                   new Thread(new Runnable() {
                       @Override
                       public void run() {
                           String msg = get();
                           handler.sendEmptyMessage(1);
   
                       }
   
   
                   }) {
                   }.start();
               }
           });
   
   
       }
   
       private String get() {
           try {
               URL url = new URL("http://10.0.2.2/star_male.json");
               HttpURLConnection connection = (HttpURLConnection) url.openConnection();
               connection.setRequestMethod("GET");
               connection.setConnectTimeout(6000);
               if (connection.getResponseCode() == HttpURLConnection.HTTP_OK) {
                   InputStream in = connection.getInputStream();
                   byte[] b = new byte[1024];
                   int len = 0;
                   ByteArrayOutputStream baos = new ByteArrayOutputStream();
                   while ((len = in.read(b)) > -1) {
                       baos.write(b, 0, len);
                   }
                 str = new String(baos.toByteArray());
                   return str;
   
   
               }
           } catch (ProtocolException e) {
               e.printStackTrace();
           } catch (MalformedURLException e) {
               e.printStackTrace();
           } catch (IOException e) {
               e.printStackTrace();
           }
           return "";
   
   
       }
   }