9.18

import android.database.Cursor;

import android.database.sqlite.SQLiteDatabase;

import android.os.Bundle;

import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;

 

public class MainActivity extends AppCompatActivity {

 

    private DatabaseHelper dbHelper;

    private TextView textView;

 

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

 

        textView = findViewById(R.id.textView);

        dbHelper = new DatabaseHelper(this);

 

        // 插入数据

        insertData("JohnDoe", "john@example.com");

 

        // 获取数据

        String users = getUsers();

        textView.setText(users);

    }

 

    private void insertData(String username, String email) {

        SQLiteDatabase db = dbHelper.getWritableDatabase();

        String insertSQL = "INSERT INTO users (username, email) VALUES (?, ?)";

        db.execSQL(insertSQL, new Object[]{username, email});

    }

 

    private String getUsers() {

        SQLiteDatabase db = dbHelper.getReadableDatabase();

        String selectSQL = "SELECT * FROM users";

        Cursor cursor = db.rawQuery(selectSQL, null);

 

        StringBuilder users = new StringBuilder();

        while (cursor.moveToNext()) {

            int id = cursor.getInt(cursor.getColumnIndex("id"));

            String username = cursor.getString(cursor.getColumnIndex("username"));

            String email = cursor.getString(cursor.getColumnIndex("email"));

            users.append("ID: ").append(id)

                 .append(", Username: ").append(username)

                 .append(", Email: ").append(email)

                 .append("\n");

        }

        cursor.close();

        return users.toString();

    }

}