Android开发笔记（三十）SQLite数据库基础操作

		//创建数据库，如果已存在则打开
		SQLiteDatabase db = getApplicationContext().openOrCreateDatabase("test.db", Context.MODE_PRIVATE, null);
		//删除数据库
		getApplicationContext().deleteDatabase("test.db");

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

public class TestDBHelper extends SQLiteOpenHelper {
	private static final String TAG = "TestDBHelper";
	
	private static final String DB_NAME = "test.mDB";
	private static final int DB_VERSION = 1;
	private static TestDBHelper mHelper = null;
	private SQLiteDatabase mDB = null;

	private TestDBHelper(Context context) {
		super(context, DB_NAME, null, DB_VERSION);
	}

	private TestDBHelper(Context context, int version) {
		super(context, DB_NAME, null, version);
	}

	public static TestDBHelper getInstance(Context context, int version) {
		if (version > 0 && mHelper == null) {
			mHelper = new TestDBHelper(context, version);
		} else if (mHelper == null) {
			mHelper = new TestDBHelper(context);
		}
		return mHelper;
	}

	public SQLiteDatabase openReadLink() {
		Log.d(TAG, "openReadLink");
		if (mDB == null || mDB.isOpen() != true) {
			mDB = mHelper.getReadableDatabase();
		}
		return mDB;
	}

	public SQLiteDatabase openLink() {
		Log.d(TAG, "openLink");
		if (mDB == null || mDB.isOpen() != true) {
			mDB = mHelper.getWritableDatabase();
		}
		return mDB;
	}

	public void closeLink() {
		Log.d(TAG, "closeLink");
		if (mDB != null && mDB.isOpen() == true) {
			mDB.close();
			mDB = null;
		}
	}
	
	public String getDBName() {
		if (mHelper != null) {
			return mHelper.getDatabaseName();
		} else {
			return DB_NAME;
		}
	}
	
	@Override
	public void onCreate(SQLiteDatabase db) {
		Log.d(TAG, "onCreate");
		String create_sql = "CREATE TABLE IF NOT EXISTS person ("
				+ "_id INTEGER PRIMARY KEY  AUTOINCREMENT  NOT NULL ,"
				+ "name VARCHAR NOT NULL," + "age INTEGER  NOT NULL" + ")";
		Log.d(TAG, "create_sql:" + create_sql);
		db.execSQL(create_sql);
	}

	@Override
	public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
		Log.d(TAG, "onUpgrade");
		if (newVersion == 10) {
			String alter_sql = "ALTER TABLE person ADD COLUMN company VARCHAR";
			Log.d(TAG, "alter_sql:" + alter_sql);
			db.execSQL(alter_sql);
		}
	}

}