案例5-3,编写程序演示sqlite数据库操作。android

以下是一个简单的 Android 应用程序，演示如何使用 SQLite 数据库进行 CRUD 操作：

1. 创建一个新的 Android 项目，并在 build.gradle 文件中添加以下依赖：

dependencies {
    implementation 'androidx.appcompat:appcompat:1.2.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
    implementation 'androidx.recyclerview:recyclerview:1.1.0'
    implementation 'androidx.cardview:cardview:1.0.0'
    implementation 'androidx.sqlite:sqlite:2.1.0'
}

2. 创建一个新的数据库帮助器类 DBHelper，继承自 SQLiteOpenHelper：

public class DBHelper extends SQLiteOpenHelper {

    private static final String DATABASE_NAME = "my_db";
    private static final int DATABASE_VERSION = 1;

    private static final String TABLE_NAME = "my_table";
    private static final String COLUMN_ID = "_id";
    private static final String COLUMN_NAME = "name";
    private static final String COLUMN_AGE = "age";

    private static final String CREATE_TABLE =
            "CREATE TABLE " + TABLE_NAME +
                    " (" +
                    COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
                    COLUMN_NAME + " TEXT, " +
                    COLUMN_AGE + " INTEGER" +
                    ")";

    public DBHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(CREATE_TABLE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
        onCreate(db);
    }
}

3. 在 MainActivity 中，初始化 DBHelper 实例，并使用 SQLiteDatabase 实例进行 CRUD 操作：

public class MainActivity extends AppCompatActivity {

    private RecyclerView recyclerView;
    private RecyclerView.Adapter adapter;

    private List<Person> personList = new ArrayList<>();

    private DBHelper dbHelper;
    private SQLiteDatabase db;

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

        dbHelper = new DBHelper(this);
        db = dbHelper.getWritableDatabase();

        recyclerView = findViewById(R.id.recycler_view);
        adapter = new PersonAdapter(personList);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        recyclerView.setAdapter(adapter);

        findViewById(R.id.button_add).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                addPerson();
            }
        });

        findViewById(R.id.button_query).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                queryPerson();
            }
        });
    }

    private void addPerson() {
        ContentValues values = new ContentValues();
        values.put(DBHelper.COLUMN_NAME, "Tom");
        values.put(DBHelper.COLUMN_AGE, 20);
        db.insert(DBHelper.TABLE_NAME, null, values);
    }

    private void queryPerson() {
        Cursor cursor = db.query(DBHelper.TABLE_NAME, null, null, null, null, null, null);
        if (cursor.moveToFirst()) {
            personList.clear();
            do {
                int id = cursor.getInt(cursor.getColumnIndex(DBHelper.COLUMN_ID));
                String name = cursor.getString(cursor.getColumnIndex(DBHelper.COLUMN_NAME));
                int age = cursor.getInt(cursor.getColumnIndex(DBHelper.COLUMN_AGE));
                Person person = new Person(id, name, age);
                personList.add(person);
            } while (cursor.moveToNext());
            adapter.notifyDataSetChanged();
        }
        cursor.close();
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        db.close();
        dbHelper.close();
    }
}

4. 创建一个 Person 类，用来封装数据库中的每一条记录：

public class Person {

    private int id;
    private String name;
    private int age;

    public Person(int id, String name, int age) {
        this.id = id;
        this.name = name;
        this.age = age;
    }

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }
}

5. 创建一个 RecyclerView.Adapter 类，用来展示数据库中的每一条记录：

public class PersonAdapter extends RecyclerView.Adapter<PersonAdapter.ViewHolder> {

    private List<Person> personList;

    public PersonAdapter(List<Person> personList) {
        this.personList = personList;
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_person, parent, false);
        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        Person person = personList.get(position);
        holder.textViewId.setText(String.valueOf(person.getId()));
        holder.textViewName.setText(person.getName());
        holder.textViewAge.setText(String.valueOf(person.getAge()));
    }

    @Override
    public int getItemCount() {
        return personList.size();
    }

    static class ViewHolder extends RecyclerView.ViewHolder {

        TextView textViewId;
        TextView textViewName;
        TextView textViewAge;

        public ViewHolder(@NonNull View itemView) {
            super(itemView);
            textViewId = itemView.findViewById(R.id.text_view_id);
            textViewName = itemView.findViewById(R.id.text_view_name);
            textViewAge = itemView.findViewById(R.id.text_view_age);
        }
    }
}

6. 创建一个 item_person.xml 布局文件，用来展示每一条记录：

<?xml version="1.0" encoding="utf-8"?>
<androidx.cardview.widget.CardView
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_margin="8dp">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:padding="16dp">

        <TextView
            android:id="@+id/text_view_id"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="ID"/>

        <TextView
            android:id="@+id/text_view_name"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="Name"/>

        <TextView
            android:id="@+id/text_view_age"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="Age"/>

    </LinearLayout>

</androidx.cardview.widget.CardView>

7. 运行应用程序，点击“Add”按钮添加一条记录，点击“Query”按钮查询所有记录，并展示在 RecyclerView 中。

以上就是一个简单的 Android 应用程序，演示如何使用 SQLite 数据库进行 CRUD 操作。