android 子线程使用handle修改主线线程内容

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".HandleActivity"> <TextView
android:id="@+id/textView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="129dp"
android:layout_marginTop="69dp"
android:text="@string/显示内容"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" /> <Button
android:id="@+id/button3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="116dp"
android:layout_marginTop="248dp"
android:text="@string/button2"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

package com.example.myapplication;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;public class HandleActivity extends AppCompatActivity {
private Button btn;
private TextView tv; @Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_handle); btn = findViewById(R.id.button3);
tv = findViewById(R.id.textView); btn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
new Thread(){ @Override
public void run() {
super.run();
Message msg=new Message();
msg.what = 1;
handler.sendMessage(msg);
}
}.start();
}
});
} Handler handler = new Handler(){
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
if(msg.what==1){
tv.setText("子线程使用handle修改主线程控件内容");
}
}
};
}

Handler handler = new Handler() {
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
Toast.makeText(getApplicationContext(), (String) msg.obj, Toast.LENGTH_SHORT).show();
}
};

Message message = Message.obtain();
message.obj = str;
handler.sendMessage(message);