Android 数据库 使用实例

MyDatabaseHelper.java 的内容如下：

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.widget.Toast;

/**
 * Created by toby on 17-12-28.
 */

public class MyDatabaseHelper extends SQLiteOpenHelper {

    private static final String CREATE_BOOK = "create table Book (" +
            "id integer primary key autoincrement, " +
            "author text, " +
            "price real, " +
            "pages integer, " +
            "name text)";

    private static final String CREATE_CATEGORY = "create table Category (" +
            "id integer primary key autoincrement, " +
            "category_name text, " +
            "category_code integer)";

    private Context mContext;

    public MyDatabaseHelper(Context context, String name, SQLiteDatabase.CursorFactory factory,
                            int version) {
        super(context, name, factory, version);
        mContext = context;
    }

    @Override
    public void onCreate(SQLiteDatabase sqLiteDatabase) {
        sqLiteDatabase.execSQL(CREATE_BOOK);
        sqLiteDatabase.execSQL(CREATE_CATEGORY);
        Toast.makeText(mContext, "Create succeeded", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int oldVersion, int newVersion) {
        switch (oldVersion) {
            case 1:
                sqLiteDatabase.execSQL(CREATE_CATEGORY);
                // 不要加 break，以保证每次数据库的修改都会被执行
                // break;
            case 2:
                sqLiteDatabase.execSQL("alter table Book add column category_id integer");
                // 不要加 break，以保证每次数据库的修改都会被执行
                // break;
            default:
        }
    }
}

使用的实例代码如下：

import android.app.Activity;
import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.util.Log;
import android.view.View;

public class MainActivity extends Activity {

    private static final String TAG = "MainActivity";
    private MyDatabaseHelper dbHelper;

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

        dbHelper = new MyDatabaseHelper(this, "BookStore.db", null, 2);
    }

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

    public void create(View view) {
        dbHelper.getWritableDatabase();
    }

    public void add(View view) {
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put("name", "The first");
        values.put("author", "None");
        values.put("pages", 123);
        values.put("price", 12.34);
        // 第二个参数用于在未指定添加数据的情况下给某些可为空的列自动赋值 NULL，一般填 null
        db.insert("Book", null, values);

        values.clear();

        values.put("name", "The Second");
        values.put("author", "None");
        values.put("pages", 234);
        values.put("price", 23.45);
        db.insert("Book", null, values);
    }

    public void update(View view) {
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put("price","10.00");
        // 不指定，第三和第四个参数，将会更新所有行
        db.update("Book", values, "name = ?", new String[] {"The first"});
    }

    public void delete(View view) {
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        // 第二个和第三个参数如果不指定将会删除所有行
        db.delete("Book", "pages > ?", new String[] {"200"});
    }

    public void query(View view) {
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        Cursor cursor = db.query("Book", null, null, null,
                null, null, null);

        if (cursor.moveToFirst()) {
            do {
                String value = cursor.getString(cursor.getColumnIndex("name"));
                Log.d(TAG, "Book name is " + value);

                value = cursor.getString(cursor.getColumnIndex("author"));
                Log.d(TAG, "Book author is " + value);

                value = cursor.getString(cursor.getColumnIndex("pages"));
                Log.d(TAG, "Book pages is " + value);

                value = cursor.getString(cursor.getColumnIndex("price"));
                Log.d(TAG, "Book price is " + value);
            } while (cursor.moveToNext());

            cursor.close();
        }
    }

    public void replace(View view) {
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        db.beginTransaction();
        try {
            db.delete("Book", null, null);
//            if (true) { // 抛出一个异常测试事务
//                throw new NullPointerException();
//            }
            ContentValues values = new ContentValues();
            values.put("name", "The Third");
            values.put("author", "Toby");
            values.put("pages", 720);
            values.put("price", 23.45);
            db.insert("Book", null, values);
            db.setTransactionSuccessful();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            db.endTransaction();
        }
    }
}

布局文件的代码如下：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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="com.syberos.learnandroid.MainActivity">

    <Button
        android:id="@+id/create"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true"
        android:layout_marginStart="136dp"
        android:layout_marginTop="22dp"
        android:text="@string/create"
        android:onClick="create"
        />

    <Button
        android:id="@+id/add"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignStart="@+id/create"
        android:layout_below="@+id/create"
        android:layout_marginTop="17dp"
        android:onClick="add"
        android:text="@string/add"
        />

    <Button
        android:id="@+id/update"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignStart="@+id/add"
        android:layout_below="@+id/add"
        android:layout_marginTop="11dp"
        android:onClick="update"
        android:text="@string/update" />

    <Button
        android:id="@+id/delete"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignStart="@+id/update"
        android:layout_below="@+id/update"
        android:layout_marginTop="15dp"
        android:onClick="delete"
        android:text="@string/delete" />

    <Button
        android:id="@+id/query"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignStart="@+id/delete"
        android:layout_below="@+id/delete"
        android:layout_marginTop="14dp"
        android:text="@string/query"
        android:onClick="query"
        />

    <Button
        android:id="@+id/replace"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignStart="@+id/query"
        android:layout_below="@+id/query"
        android:text="@string/replace"
        android:onClick="replace"
        />


</RelativeLayout>

string 文件的内容如下：

<resources>
    <string name="app_name">LearnAndroid</string>
    <string name="create">create</string>
    <string name="add">add</string>
    <string name="update">update</string>
    <string name="delete">delete</string>
    <string name="query">query</string>
    <string name="replace">replace</string>
</resources>

本文参考自 《Android 第一行代码》