AS Room編②解説part4～Roomを使って、登録したデータを別のActivityに表示する～

MainActivity.java

package com.example.listdatabase;

import androidx.appcompat.app.AppCompatActivity;
import androidx.room.Dao;

import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import com.google.android.material.snackbar.Snackbar;

import java.sql.Timestamp;
import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {
    static AppDatabase db;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        TextView showData = findViewById(R.id.showData);

        Button registerBtn = findViewById(R.id.registerBtn);
        db = AppDatabaseSingleton.getInstance(getApplicationContext());
        registerBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                new Thread(new Runnable(){

                    @Override
                    public void run() {
                        // 本質的な処理
                        UserDao userDao = db.userDao();
                        EditText editName = findViewById(R.id.editName);
                        userDao.insert(new User(editName.getText().toString()));
                    }
                }).start();

                Snackbar.make(MainActivity.this,view,"1件のデータが登録されました。",Snackbar.LENGTH_LONG).show();

            }
        });

        Button displayBtn = findViewById(R.id.displayBtn);
        displayBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                startActivity(new Intent(MainActivity.this,SecondActivity.class));
            }
        });

    }

}

activity_main.xml

<?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"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity"
    android:gravity="center_horizontal"
    android:orientation="vertical">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="名前："/>
    <EditText
        android:id="@+id/editName"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>
    <Button
        android:id="@+id/registerBtn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="登録"/>
    <TextView
        android:id="@+id/showData"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>

    <Button
        android:id="@+id/displayBtn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="一覧表示"/>

</LinearLayout>

SecondActivity.java

package com.example.listdatabase;

import static com.example.listdatabase.MainActivity.db;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.List;

public class SecondActivity extends AppCompatActivity {


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);

        new Thread(new Runnable(){

            @Override
            public void run() {
                // 本質的な処理
                UserDao userDao = db.userDao();
                List<User> atList = userDao.getAll();
                ArrayList<String> arrayList = new ArrayList<>();
                for(User user:atList){
                    arrayList.add(user.getName());
                }

                ListView secondView = findViewById(R.id.secondView);
                ArrayAdapter<String> arrayAdapter = new ArrayAdapter<>(SecondActivity.this,android.R.layout.simple_list_item_1,arrayList);

                secondView.setAdapter(arrayAdapter);

            }
        }).start();

        ListView secondView = findViewById(R.id.secondView);
        secondView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {

            }
        });


    }
}

activity_second.xml

<?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"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".SecondActivity">

    <ListView
        android:id="@+id/secondView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>

</LinearLayout>

UserDao(インターフェース）、User.java、AppDatabase.java、AppDatabaseSingleton.javaは以前と同じです。