Handler的基本用法

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

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 "";


    }
}