Android开发之ContentProvider结合LoaderManager加载数据
ContentProvider作为Android的四大存储方式之一，有着广泛的应用性，它暴露了数据地址，可以让其他应用访问数据，可以用于存储图片、通讯录等信息，这篇博文将详细介绍ContentProvider、URIMatcher，LoaderManager,cursorAdapter的方法使用与介绍。使用ContentProvider的时候一定要注意在manifest清单文件中像Acticity文件一样，声明其属性。如图所示
此外因为我们是用loadermanager来加载数据，MainAcitivity类要实现LoaderCallback接口。按照惯例我们还是看下谷歌官方文档对contentprovider的解释，ContentProvider管理一个结构化的数据集。它封装了数据,并提供定义数据安全机制。ContentProvider的标准接口实现多线程机制来连接数据,一般是用loaderManager异步加载数据。当你想要访问数据在一个ContentProvider,我们使用ContentResolver对象在应用程序的上下文中作为沟通方法。ContentResolver用来解析请求码返还数据。
我们先看看一下本次介绍的工程的目录结构
MainActivity的代码
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package com.example.f14_contentprovider;
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import java.util.ArrayList;
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import java.util.HashMap;
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import java.util.List;
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import android.net.Uri;
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import android.os.Bundle;
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import android.app.Activity;
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import android.app.LoaderManager;
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import android.app.LoaderManager.LoaderCallbacks;
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import android.content.ContentResolver;
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import android.content.ContentValues;
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import android.content.CursorLoader;
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import android.content.Loader;
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import android.database.Cursor;
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import android.view.Menu;
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import android.view.View;
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import android.widget.Button;
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import android.widget.ListView;
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import android.widget.SimpleCursorAdapter;
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public class MainActivity extends Activity implements LoaderCallbacks {
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private Button button;
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private ListView listView;
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private LoaderManager loaderManager;
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private SimpleCursorAdapter adapter;
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@Override
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protected void onCreate(Bundle savedInstanceState) {
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super.onCreate(savedInstanceState);
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setContentView(R.layout.activity_main);
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button = (Button) this.findViewById(R.id.button1);
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listView = (ListView) this.findViewById(R.id.listView1);
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button.setOnClickListener(new View.OnClickListener() {
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@Override
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public void onClick(View v) {
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// TODO Auto-generated method stub
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ContentResolver resolver = getContentResolver();
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Uri uri = Uri
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.parse("content://com.example.f14_contentprovider.PersonContentProvider/person");
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ContentValues values = new ContentValues();
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values.put("name", "jack");
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values.put("address", "hangzhou");
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resolver.insert(uri, values);
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loaderManager.restartLoader(1001, null, MainActivity.this);
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}
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});
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loaderManager = getLoaderManager();
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loaderManager.initLoader(1001, null, this);
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}
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@Override
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public Loader onCreateLoader( int id, Bundle args) {
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// TODO Auto-generated method stub
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/**
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* CursorLoader该类用于加载程序,查询ContentResolver并返回一个指针。这个类实现了装载机协议查询游标的标准方法,
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* 基于AsyncTaskLoader执行游标查询在一个后台线程,以便它不会阻止应用程序的UI。
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*/
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CursorLoader loader = new CursorLoader(this);
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Uri uri = Uri
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.parse("content://com.example.f14_contentprovider.PersonContentProvider/person");
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loader.setUri(uri);
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loader.setProjection(new String[] { "name", "address" });
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return loader;
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}
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@SuppressWarnings("deprecation")
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@Override
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public void onLoadFinished(Loader arg0, Cursor arg1) {
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// TODO Auto-generated method stub
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List> list = new ArrayList>();
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// 加载数据
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while (arg1.moveToNext()) {
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HashMap map = new HashMap();
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map.put("name", arg1.getString(arg1.getColumnIndex("name")));
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map.put("address", arg1.getString(arg1.getColumnIndex("address")));
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list.add(map);
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}
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adapter = new SimpleCursorAdapter(this, R.layout.item, arg1,
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new String[] { "name", "address" }, new int[] { R.id.textView1,
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R.id.textView2 });
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listView.setAdapter(adapter);
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adapter.notifyDataSetChanged();// 若内容发生变化 触发该方法
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}
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@Override
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public void onLoaderReset(Loader arg0) {
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// TODO Auto-generated method stub
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}
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}
PersonContentProvider继承了ContentProvider的方法
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package com.example.f14_contentprovider;
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import android.content.ContentProvider;
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import android.content.ContentResolver;
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import android.content.ContentUris;
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import android.content.ContentValues;
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import android.content.UriMatcher;
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import android.database.Cursor;
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import android.database.sqlite.SQLiteDatabase;
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import android.net.Uri;
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//要在manifest文件中注册provider
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public class PersonContentProvider extends ContentProvider {
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private MyOpenHelper helper;
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private static final UriMatcher matcher = new UriMatcher(
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UriMatcher.NO_MATCH);// 专门用来匹配URI的类
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private static final int PERSONS = 1;
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private static final int PERSON = 2;
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private ContentResolver resolver;
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static {
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matcher.addURI("com.example.f14_contentprovider.PersonContentProvider",
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"person", PERSONS);
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matcher.addURI("com.example.f14_contentprovider.PersonContentProvider",
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"person/#", PERSON);
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}
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@Override
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public int delete(Uri uri, String selection, String[] selectionArgs) {
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// TODO Auto-generated method stub
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return 0;
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}
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// 当您需要匹配一个URI,调用匹配(URI),用来来建立一个查询,返回类型,插入或删除一行。
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@Override
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public String getType(Uri arg0) {
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// TODO Auto-generated method stub
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int match = matcher.match(arg0);
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switch (match) {
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case PERSONS:
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return "vnd.android.cursor.dir/person";
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case PERSON:
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return "vnd.android.cursor.item/person";
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default:
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return null;
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}
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}
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@Override
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public Uri insert(Uri uri, ContentValues values) {
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// TODO Auto-generated method stub
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SQLiteDatabase database = helper.getWritableDatabase();
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long id = database.insert("person", null, values);
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Uri rUri = ContentUris.withAppendedId(uri, id);
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resolver.notifyChange(rUri, null);
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return rUri;
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}
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@Override
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public boolean onCreate() {
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// TODO Auto-generated method stub
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helper = new MyOpenHelper(getContext());
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resolver = getContext().getContentResolver();
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return true;
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}
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@Override
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public Cursor query(Uri uri, String[] projection, String selection,
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String[] selectionArgs, String sortOrder) {
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// TODO Auto-generated method stub
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Cursor cursor = null;
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int flag = matcher.match(uri);
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SQLiteDatabase database = helper.getReadableDatabase();
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switch (flag) {
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case PERSONS:
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cursor=database.query("person", null, null, null,null, null, null);
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break;
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case PERSON:
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long _id = ContentUris.parseId(uri);
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String where_value = " _id = " + _id;
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if (selection != null && !selection.equals("")) {
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where_value += selection;
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}
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cursor = database.query("person", projection, where_value,
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selectionArgs, null, null, sortOrder);
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break;
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default:
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break;
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}
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cursor.setNotificationUri(resolver, uri);
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return cursor;
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}
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@Override
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public int update(Uri arg0, ContentValues arg1, String arg2, String[] arg3) {
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// TODO Auto-generated method stub
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return 0;
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}
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}
数据库创建类MyopenHelper
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package com.example.f14_contentprovider;
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import android.content.Context;
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import android.database.sqlite.SQLiteDatabase;
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import android.database.sqlite.SQLiteOpenHelper;
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public class MyOpenHelper extends SQLiteOpenHelper {
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private static final int DATABASE_VERSION = 1;
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private static final String PERSON_TABLE_NAME = "person";
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public MyOpenHelper(Context context) {
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super(context, PERSON_TABLE_NAME, null, DATABASE_VERSION);
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// TODO Auto-generated constructor stub
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}
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@Override
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public void onCreate(SQLiteDatabase db) {
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// TODO Auto-generated method stub
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db.execSQL("create table "
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+ PERSON_TABLE_NAME
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+ "(_id integer primary key autoincrement,name varchar(64),address varchar(64))");
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}
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@Override
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public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
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// TODO Auto-generated method stub
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}
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}