【Android篇】Handler通信机制（代码版）

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_margin="20dp"
        android:text="开始"
        android:id="@+id/btn1"
        android:onClick="startThread"/>
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/tv1"/>
</LinearLayout>

package com.example.a20221130_threadhandler;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Looper;
import android.os.Message;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
    Button btn;
    TextView textView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btn = findViewById(R.id.btn1);
        textView = findViewById(R.id.tv1);
    }
    //让子线程去运行的方法，获取字符串
    private String GetString(){
        String string="";
        StringBuilder stringBuilder=new StringBuilder();
        for(int i=0;i<10;i++){
            stringBuilder.append("sb" + i);
        }
        //沉睡4秒
        try {
            Thread.sleep(4000);
        }catch (InterruptedException i){
            i.printStackTrace();
        }
        string=stringBuilder.toString();
        return string;
    }
    //获取主线程的Handle
    Handler handler=new Handler(Looper.myLooper()){
        @Override
        public void handleMessage(@NonNull Message msg) {
            super.handleMessage(msg);
            //判断获取到的Message信息是哪个编号
            if(msg.what==0){
                String data = (String) msg.obj;
                textView.setText(data);
                Toast.makeText(MainActivity.this, "主线程收到", Toast.LENGTH_SHORT).show();
            }
        }
    };
    public void startThread(View view) {
        new Thread(new Runnable() {
            @Override
            //run()方法里面是子线程运行的，其他都是主线程，包括start()
            public void run() {
                String s = GetString();
                //创建一个Message类
                Message message=new Message();
                message.what=0;
                message.obj=s;
                //让主线程的handler对象发送信息MessageQueue即可
                handler.sendMessage(message);
            }
        }).start();
        Toast.makeText(this, "任务完成", Toast.LENGTH_SHORT).show();
    }
}