Android 数据存储——SQLite实例、判断数据库中表是否存在

本文主要记录一下Android SQLiteDatabase中如何判断数据库中表是否存在，以及测试SQLiteDatabase数据库的基本操作。有关SQLite的详细说明，可以查看转载的Android 数据存储——SQLite使用详解

例子：

AndroidManifest.xml——没有做任何修改，创建工程默认

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.wxl.handlerthread"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="19" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.wxl.handlerthread.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

MainActivity.java

package com.example.sqlite;

import android.os.Bundle;
import android.util.Log;
import android.app.Activity;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;

public class MainActivity extends Activity {
	private SQLiteDatabase db1;
//	private SQLiteDatabase db2;
	private MyDatabaseUtil myDatabaseUtil;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //参数二是数据库文件名
        myDatabaseUtil = new MyDatabaseUtil(this, "db1.db", null, 1);

        db1 = this.openOrCreateDatabase("db1.db", Context.MODE_PRIVATE, null);
        /*/data/data/com.example.sqlite/databases必须存在，否则创建出错，最后是databases而不是database，不要忘了加's'*/
//        db2 = SQLiteDatabase.openOrCreateDatabase("/data/data/com.example.sqlite/databases/db2.db3",null);

        /*创建表，并判断是否已经存在此表，没创建，则创建并初始化*/
        if (!myDatabaseUtil.tabIsExist("person")) {
        	db1.execSQL("CREATE TABLE person (_id integer primary key autoincrement, name varchar(20))");
        	ContentValues values =new ContentValues();
            for(int i=0;i<10;i++){
                    values.put("name", "name "+ i);
                   db1.insert("person", "_id", values);
            }
        }else {
        	Log.i("+++++++++++", "已经创建了，无需再创建");
        }

        /*更新数据库*/
        ContentValues values =new ContentValues();
        values.put("name", "wxl");
        db1.update("person", values, "_id=1", null);
        db1.update("person", values, "_id=?", new String[]{"5"});

        /*查询数据*/
        Cursor c = db1.query("person", null, null, null, null, null, null);
        c.moveToFirst();
	    while(!c.isAfterLast()){
	    	int index = c.getColumnIndex("name");
	        Log.d("SQLite", c.getString(index));
	        c.moveToNext();
	    }

	    c = db1.rawQuery("select * from person", null);
	    c.moveToFirst();
	    while(!c.isAfterLast()){
	    	int index = c.getColumnIndex("name");
	        Log.d("SQLite", c.getString(index));
	        c.moveToNext();
	    }

    }

    public class MyDatabaseUtil extends SQLiteOpenHelper{

		public MyDatabaseUtil(Context context, String name,
				CursorFactory factory, int version) {
			super(context, name, factory, version);
			// TODO Auto-generated constructor stub
		}

		@Override
		public void onCreate(SQLiteDatabase arg0) {
			// TODO Auto-generated method stub
		}

		@Override
		public void onUpgrade(SQLiteDatabase arg0, int arg1, int arg2) {
			// TODO Auto-generated method stub
		}

		/**
         * 判断某张表是否存在
         * @param tabName 表名
         * @return
         */
        public boolean tabIsExist(String tabName){
                boolean result = false;
                if(tabName == null){
                        return false;
                }
                SQLiteDatabase db = null;
                Cursor cursor = null;
                try {
                        db = this.getReadableDatabase();//此this是继承SQLiteOpenHelper类得到的
                        String sql = "select count(*) as c from sqlite_master where type ='table' and name ='"+tabName.trim()+"' ";
                        cursor = db.rawQuery(sql, null);
                        if(cursor.moveToNext()){
                                int count = cursor.getInt(0);
                                if(count>0){
                                        result = true;
                                }
                        }

                } catch (Exception e) {
                        // TODO: handle exception
                }
                return result;
        }

    }

}

其中getReadableDatabase()方法是SQLiteOpenHelper类中的

创建表并初始化得到的表数据如下：

更新数据得到的表数据：

查询数据表的数据显示结果如下：