持久化存储--3、SQLite 数据库存储

sqlite：轻量级的关系型数据库，android提供sqliteOpenHelper帮助类，方便对数据库创建和升级。抽象方法onCreate()和 onUpgrade()，创建和升级
数据库逻辑。
实例方法getReadableDatabase() 和
getWritableDatabase()，创建或打开现有数据库。

public class MyDatabaseHelper extends sqliteOpenHelper {

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

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

    private Context mContext;
    //重写构造方法：Context，数据库名，查询数据时返回自定义Cursor，数据库版本号
    public MyDatabaseHelper(Context context,String name,CursorFactory factory,int version) {
        super(context,name,factory,version);
        mContext = context;
    }

    @Override
    public void onCreate(sqliteDatabase db) {
        db.execsql(CREATE_BOOK);
        db.execsql(CREATE_CATEGORY);
        Toast.makeText(mContext,"Create succeeded",Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onUpgrade(sqliteDatabase db,int oldVersion,int newVersion) {
        db.execsql("drop table if exists Book");
        db.execsql("drop table if exists Category");
        onCreate(db);
    }

}

1、创建数据库：

dbHelper = new MyDatabaseHelper(this,"BookStore.db",null,2);
        Button createDatabase = (Button) findViewById(R.id.create_database);
        createDatabase.setonClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                dbHelper.getWritableDatabase();
            }
        });

生成BookStore.db数据库

使用sqliteSpy软件打开，可以看到Book表，里面有5种数据类型

2、添加数据

Button addData = (Button) findViewById(R.id.add_data);
        addData.setonClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                sqliteDatabase db = dbHelper.getWritableDatabase();
                ContentValues values = new ContentValues();
                values.put("name","The Da Vinci Code");
                values.put("author","Dan brown");
                values.put("pages",454);
                values.put("price",16.96);
                db.insert("Book",null,values);
                values.clear();
                values.put("name","The Lost Symbol");
                values.put("author",510);
                values.put("price",19.95);
                db.insert("Book",values);
            }
        });

可以看到数据库里面的数据

3、更新数据

Button updateData = (Button) findViewById(R.id.update_data);
        updateData.setonClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                sqliteDatabase db = dbHelper.getWritableDatabase();
                ContentValues values = new ContentValues();
                values.put("price",10.99);
                db.update("Book",values,"name = ?",new String[] { "The Da Vinci Code" });
            }
        });

更新数据，可以看到价格变成了10.99

4、删除数据

Button deleteButton = (Button) findViewById(R.id.delete_data);
        deleteButton.setonClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                sqliteDatabase db = dbHelper.getWritableDatabase();
                db.delete("Book","pages > ?",new String[] { "500" });
            }
        });

删除数据,可以看到name数据The Lost Symbol被删除，其他项也被删除：

5、遍历数据

Button queryButton = (Button) findViewById(R.id.query_data);
        queryButton.setonClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                sqliteDatabase db = dbHelper.getWritableDatabase();
                Cursor cursor = db.query("Book",null);
                if (cursor.movetoFirst()) {
                    do {
                        String name = cursor.getString(cursor
                                .getColumnIndex("name"));
                        String author = cursor.getString(cursor
                                .getColumnIndex("author"));
                        int pages = cursor.getInt(cursor
                                .getColumnIndex("pages"));
                        double price = cursor.getDouble(cursor
                                .getColumnIndex("price"));
                        Log.d("MainActivity","book name is " + name);
                        Log.d("MainActivity","book author is " + author);
                        Log.d("MainActivity","book pages is " + pages);
                        Log.d("MainActivity","book price is " + price);
                    } while (cursor.movetoNext());
                }
                cursor.close();
            }
        });

设置断点，debug模式下，单击query按键，运行到断点处，可以在watch窗口看到各个变量的数据：

6、代替数据

Button replaceData = (Button) findViewById(R.id.replace_data);
        replaceData.setonClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                sqliteDatabase db = dbHelper.getWritableDatabase();
                db.beginTransaction();
                try {
                    db.delete("Book",null);
// if (true) {
// throw new NullPointerException();
// }
                    ContentValues values = new ContentValues();
                    values.put("name","Game of Thrones");
                    values.put("author","George Martin");
                    values.put("pages",720);
                    values.put("price",20.85);
                    db.insert("Book",values);
                    db.setTransactionSuccessful();
                } catch (Exception e) {
                    e.printstacktrace();
                } finally {
                    db.endTransaction();
                }
            }
        });

可以看到name数据被代替：