android contentProvider用法

存储数据的方式很多，在android平时有sharedpreference file  sqlite等．这里主要分析下数据库存储．为了共享数据库．可以让数据库披上contentprovider 外衣．具体看例子
[size=12]package com.misoo.SQ02;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;
import android.app.ListActivity;
import android.content.Intent;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.view.View;
import android.widget.ListView;
import android.widget.SimpleAdapter;
public class ac01 extends ListActivity {
public static int g_variable;
public static final String AUTHORITY = "com.misoo.provider.SQ02";
public static final Uri CONTENT_URI =
Uri.parse("content://" + AUTHORITY + "/StudentTable");
private static final String[] PROJECTION = new String[] {
"stud_no", "stud_name" };
@Override protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Intent intent = getIntent();
if (intent.getData() == null) intent.setData(CONTENT_URI);
Cursor cur = getContentResolver().query(getIntent().getData(),
PROJECTION, null, null, null);
ArrayList<Map<String, Object>> coll
= new ArrayList<Map<String, Object>>();
Map<String, Object> item;
cur.moveToFirst();
while(!cur.isAfterLast()) {
item = new HashMap<String, Object>();
item.put("c1", cur.getString(0) + ", " + cur.getString(1));
coll.add(item);
cur.moveToNext(); }
this.setListAdapter(new SimpleAdapter(this, coll,
android.R.layout.simple_list_item_1, new String[] { "c1" },
new int[] {android.R.id.text1})); }
@Override
protected void onListItemClick(ListView l, View v, int position, long id){
finish();
}
}
package com.misoo.SQ02;
import android.content.ContentProvider;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.net.Uri;
import android.util.Log;
public class DataProvider extends ContentProvider {
private static final String DATABASE_NAME = "StudDB_2.db";
private static final int DATABASE_VERSION = 2;
private static final String TABLE_NAME = "StudentTable";
private static class DatabaseHelper extends SQLiteOpenHelper {
DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override public void onCreate(SQLiteDatabase db) {
db.execSQL("Create TABLE " + TABLE_NAME + " ("
+ "stud_no" + " TEXT," + "stud_name" + " TEXT" + ");");
String sql_1 = "insert into "+ TABLE_NAME +
" (stud_no, stud_name) values('S108', 'Lily Chen');";
String sql_2 = "insert into " + TABLE_NAME +
" (stud_no, stud_name) values('S201', 'Tom Kao');";
String sql_3 = "insert into " + TABLE_NAME +
" (stud_no, stud_name) values('S333', 'Peter Rabbit');";
try {
db.execSQL(sql_1); db.execSQL(sql_2); db.execSQL(sql_3);
} catch (SQLException e) { Log.e("ERROR", e.toString()); }
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {}
}
private DatabaseHelper mOpenHelper;
@Override public boolean onCreate() {
mOpenHelper = new DatabaseHelper(getContext());
return true;
}
@Override public Cursor query(Uri uri, String[] projection, String selection,
String[] selectionArgs, String sortOrder) {
SQLiteDatabase db = mOpenHelper.getReadableDatabase();
Cursor c = db.query(TABLE_NAME, projection, null, null, null, null, null);
return c;
}
@Override public String getType(Uri uri)
{ return null; }
@Override public Uri insert(Uri uri, ContentValues initialValues)
{ return uri; }
@Override public int delete(Uri uri, String where, String[] whereArgs)
{ return 0; }
@Override public int update(Uri uri, ContentValues values,
String where, String[] whereArgs)
{ return 0; }
}[/size]

从例子可以看出。不管怎么表达，最后要得到SQLiteDatabase引用．然后用这个引用去操作数据库．在这里通过contentprovide 包了SQLlitOpenhelper ，通过这个来创建数据库．创建表．然后通过getContentResolver 来操作数据库．这个代码应该不难，关键我想，系统如何知道我要操作哪个数据库里的哪个表呢？

这需要用户指定
public static final String AUTHORITY = "com.misoo.provider.SQ02";
public static final Uri CONTENT_URI =
Uri.parse("content://" + AUTHORITY + "/StudentTable");

这两句就是指定了哪个数据库，指定了哪个表．　这说明在manifest.xml 里一定要加上这么几句

<provider android:name="DataProvider"
android:authorities="com.misoo.provider.SQ02">
</provider>

有了这个东西就知道是哪个数据了．就可以开始操作了．