在 Android中,对于数据的存贮,有几种方式,有文件方式,有文件式数据库方式,网络数据,Android自带了一个SQLite数据库,做嵌入开发的人对这个跨平台的本地文件数据库一定不会陌生,在Android对于数据的访问,提出了新的方式,ContentProvider方式,我们首先来看看SQLite在 Android中的使用,在Android中有最简单的使用方式,就是利Context对象的openorCreateDatabase
我们来看看一段代码:
- import android.app.Activity;
- import android.content.Intent;
- import android.database.Cursor;
- import android.database.sqlite.SQLiteDatabase;
- import android.os.Bundle;
- import android.view.Menu;
- import android.view.MenuItem;
- import android.widget.TextView;
- public class DBActivity extends Activity {
- private SQLiteDatabase mdb = null;
- /** Called when the activity is first created. */
- @Override
- public void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- initDatabase();
- setContentView(R.layout.main);
- }
- @Override
- public boolean onCreateOptionsMenu(Menu menu) {
- // TODO Auto-generated method stub
- super.onCreateOptionsMenu(menu);
- menu.add(1, Menu.FIRST +1, 1, "GetName");
- menu.add(1, Menu.FIRST +2, 2, "Test");
- return true;
- }
- public boolean onOptionsItemSelected(MenuItem item) {
- // TODO Auto-generated method stub
- super.onOptionsItemSelected(item);
- switch (item.getItemId())
- {
- case Menu.FIRST+ 1:
- {
- TextView tv = (TextView)this.findViewById(R.id.view_main);
- tv.setText(this.getName());
- break;
- }
- case Menu.FIRST + 2:
- {
- this.setTitle("Del Item...");
- break;
- }
- }
- return true;
- }
- private void initDatabase()
- {
- mdb = this.openOrCreateDatabase("dbfile", 0, null);
- String sql_create = "create table test (id int, name TEXT)";
- mdb.execSQL(sql_create);
- String sql_insert = "insert into test(id, name) values(3, 'name3')";
- mdb.execSQL(sql_insert);
- }
- private String getName()
- {
- String name = null;
- Cursor cur = mdb.rawQuery("select * from test", null);
- cur.moveToFirst();
- while (!cur.isLast())
- {
- name = name + cur.getString(1)+ "\r\n";
- cur.moveToNext();
- }
- return name;
- }
- }
我们再来看看单独使用SQLiteOpenHelper方式:
先由SQLiteOpenHelper继承一个数据库操作类,其中onCreate, onUpgrade必须重载并实现,
- import android.content.Context;
- import android.database.Cursor;
- import android.database.sqlite.SQLiteDatabase;
- import android.database.sqlite.SQLiteOpenHelper;
- public class DatabaseHelper extends SQLiteOpenHelper {
- @Override
- public void onCreate(SQLiteDatabase db) {
- // TODO Auto-generated method stub
- }
- @Override
- public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
- // TODO Auto-generated method stub
- }
- public DatabaseHelper(Context ct,String dbName)
- {
- super(ct,dbName,null,1);
- }
- public boolean insert(String insert)
- {
- this.getWritableDatabase().execSQL(insert);
- return true;
- }
- public boolean update(String update)
- {
- this.getWritableDatabase().execSQL(update);
- return true;
- }
- public boolean delete(String del)
- {
- this.getWritableDatabase().execSQL(del);
- return true;
- }
- public Cursor query(String query)
- {
- Cursor cur = this.getReadableDatabase().rawQuery(query, null);
- return cur;
- }
- }
再创建一个使用者(消费者)
- import android.app.Activity;
- import android.content.Intent;
- import android.database.Cursor;
- import android.database.sqlite.SQLiteDatabase;
- import android.os.Bundle;
- import android.view.Menu;
- import android.view.MenuItem;
- import android.widget.TextView;
- public class DBActivity extends Activity {
- private SQLiteDatabase mdb = null;
- private DatabaseHelper helper = null;
- /** Called when the activity is first created. */
- @Override
- public void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- initDatabase();
- setContentView(R.layout.main);
- }
- @Override
- public boolean onCreateOptionsMenu(Menu menu) {
- // TODO Auto-generated method stub
- super.onCreateOptionsMenu(menu);
- menu.add(1, Menu.FIRST +1, 1, "GetName");
- menu.add(1, Menu.FIRST +2, 2, "Test");
- return true;
- }
- public boolean onOptionsItemSelected(MenuItem item) {
- // TODO Auto-generated method stub
- super.onOptionsItemSelected(item);
- switch (item.getItemId())
- {
- case Menu.FIRST+ 1:
- {
- TextView tv = (TextView)this.findViewById(R.id.view_main);
- tv.setText(this.getName());
- break;
- }
- case Menu.FIRST + 2:
- {
- this.setTitle("Del Item...");
- break;
- }
- }
- return true;
- }
- private void initDatabase()
- {
- helper = new DatabaseHelper(this,"dbfile");
- //mdb = this.openOrCreateDatabase("dbfile", 0, null);
- //String sql_create = "create table test (id int, name TEXT)";
- //mdb.execSQL(sql_create);
- String sql_insert = "insert into test(id, name) values(55, 'namexx')";
- //mdb.execSQL(sql_insert);
- helper.insert(sql_insert);
- }
- private String getName()
- {
- String name = null;
- //mdb = helper.getReadableDatabase();
- Cursor cur = helper.query("select * from test");
- cur.moveToFirst();
- do
- {
- name = name + cur.getString(1)+ "\n";
- } while(cur.moveToNext());
- return name;
- }
- }
在来看看使用ContentProvider
- import android.content.ContentProvider;
- import android.content.ContentValues;
- import android.database.Cursor;
- import android.net.Uri;
- import android.widget.Toast;
- public class TestProvider extends ContentProvider {
- private DatabaseHelper mdbHelper = null;
- final static String TABLE_NAME = "test";
- @Override
- public int delete(Uri arg0, String arg1, String[] arg2) {
- mdbHelper.getWritableDatabase().delete(TABLE_NAME, arg1, arg2);
- return 0;
- }
- @Override
- public String getType(Uri uri) {
- // TODO Auto-generated method stub
- return null;
- }
- @Override
- public Uri insert(Uri uri, ContentValues values) {
- // TODO Auto-generated method stub
- mdbHelper.getWritableDatabase().insert(TABLE_NAME, "", values);
- return null;
- }
- @Override
- public boolean onCreate() {
- // TODO Auto-generated method stub
- mdbHelper = new DatabaseHelper(this.getContext(), "dbfile");
- return true;
- }
- @Override
- public Cursor query(Uri uri, String[] projection, String selection,
- String[] selectionArgs, String sortOrder) {
- Cursor cur = mdbHelper.getReadableDatabase().query(TABLE_NAME,projection,selection,null,null,null, null);
- Toast.makeText(this.getContext(), "test Cur!", Toast.LENGTH_SHORT);
- return cur;
- }
- @Override
- public int update(Uri uri, ContentValues values, String selection,
- String[] selectionArgs) {
- mdbHelper.getWritableDatabase().update(TABLE_NAME, values, selection, null);
- return 0;
- }
- }
老规矩,AndroidManifest.xml来定义这个Provider
<provider android:label="test_provider" android:authorities="com.my.provider" android:name="TestProvider">
</provider>
这里的android:authorities = "com.my.provider"是标识这个ContentProvider,调用者可以根据这个标识来找到它,
我们组合一个能找到它的Uri,
public class ProviderConst {
public static final Uri MY_TEST_URI = Uri.parse("content://com.my.provider/test");
}
content 指的是内容提供者ContentProvider。
//com.my.provider映射到我们已定义的那个ContentProvider标识
/test这个作为一个参数,传给ContentProvider,可以根据这个参数来决定操作目标,比如数据库中的哪张表,文件中的那一部分数据等。
我们来操作这个内容提供者:
- private String getName()
- {
- String name = null;
- Cursor cur = this.getContentResolver().query(ProviderConst.MY_TEST_URI,new String[]{"id","name"},null, null, null);
- if (cur == null)
- return null;
- cur.moveToFirst();
- do
- {
- name = name + cur.getString(1)+ "\n";
- } while(cur.moveToNext());
- return name;
- }