Android (SQLite 数据库与ContentProvider)
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：
package test.DB;
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，
package test.DB;
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）
package test.DB;
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;
}
}
这些代码读起来是不是有点Visual Basic的感觉？呵呵，所以，以后说不定.net,Android,java,blackberry,最终都成为一致的API，当然，这只是我们的期望，这样大家不必整天花这么多时间学这些无聊的接口了。
好了，该我们的ContentProvider出场了，与Service,BroadcastReceiver等组件一样，继承特定的Interface，在AndroidManifest.xml里声明这个ContentProvider，调用者就可以拿来使用了。
首先我们定义一个ContentProvider:
package test.DB;
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;
}
我们也可以这样使用：
private String getName()
{
String name = null;
Cursor cur = this.managedQuery(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;
}
简单的使用方法我们已了解，那么，我们来分析一下复杂的内容。
