Android 自訂ContentProvider

Android允許我們定義自己的的ContentProvider對象來共用資料，練練手，簡單來實現一下。

要使用ContentProvider來操作資料，必須要有儲存資料的場所。可以使用檔案或SQLite資料庫的方式來儲存資料，通常使用SQLite資料庫。

1，建立一個資料庫協助類，歸根結底都是它在操作資料庫。代碼如下：

package com.njue;import android.content.Context;import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteDatabase.CursorFactory;import android.database.sqlite.SQLiteOpenHelper;public class DBManager extends SQLiteOpenHelper {public static final String myProvider_table_name="myProvider_table_name";String sql="create table myProvider_table_name(id integer,name text)";public DBManager(Context context) {super(context, "myPrivoder.db", null, 1);// TODO Auto-generated constructor stub}@Overridepublic void onCreate(SQLiteDatabase arg0) {// TODO Auto-generated method stub      arg0.execSQL(sql);}@Overridepublic void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {// TODO Auto-generated method stub}}

2，建立一個myProvider類，該類繼承ContentProvider，實現其抽象方法來操作資料庫，該類引用DBManager類來獲得資料庫執行個體。

package com.njue;import android.content.ContentProvider;import android.content.ContentValues;import android.database.Cursor;import android.database.sqlite.SQLiteDatabase;import android.net.Uri;public class myProvider extends ContentProvider {    DBManager dbHelper;@Overridepublic int delete(Uri arg0, String arg1, String[] arg2) {// TODO Auto-generated method stubSQLiteDatabase db=dbHelper.getWritableDatabase();int id=db.delete(DBManager.myProvider_table_name, arg1, arg2);if(id!=0)return id;return 0;}@Overridepublic String getType(Uri uri) {// TODO Auto-generated method stubreturn null;}@Overridepublic Uri insert(Uri uri, ContentValues values) {// TODO Auto-generated method stubSQLiteDatabase db=dbHelper.getWritableDatabase();db.insert(DBManager.myProvider_table_name, "id", values);return null;}@Overridepublic boolean onCreate() {// TODO Auto-generated method stubdbHelper=new DBManager(getContext());return true;}@Overridepublic Cursor query(Uri uri, String[] projection, String selection,String[] selectionArgs, String sortOrder) {// TODO Auto-generated method stubSQLiteDatabase db=dbHelper.getWritableDatabase();Cursor c=db.query(DBManager.myProvider_table_name,projection, selection, selectionArgs, null, null, sortOrder);return c;}@Overridepublic int update(Uri uri, ContentValues values, String selection,String[] selectionArgs) {// TODO Auto-generated method stubSQLiteDatabase db=dbHelper.getWritableDatabase();int id=db.update(DBManager.myProvider_table_name, values, selection, selectionArgs);if(id!=0)return id;return 0;}}

3，ContextProvider必須聲明才能使用，因此，需要在AndroidManifest.xml設定檔中聲明。聲明很簡單，需要類名稱和授權名稱兩個屬性。

 <provider android:name="myProvider"android:authorities="com.njue.myProvider" />

 

到這裡，我們自訂的ContentProvider就完成了。我們可以在Eclipse中的File Explorer 視窗中看到自訂的ContentProvider

 

4，簡單測試

 

package com.njue;import android.app.Activity;import android.content.ContentResolver;import android.content.ContentValues;import android.database.Cursor;import android.net.Uri;import android.os.Bundle;import android.util.Log;import android.view.View;import android.widget.Button;import android.widget.EditText;import android.widget.TextView;public class Content_providerActivity extends Activity {    /** Called when the activity is first created. */ Uri uri; String AUTHORITY="content://com.njue.myProvider/myProvider_table_name"; ContentResolver cr; EditText input; Button insert; TextView show;    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);       setContentView(R.layout.main);       input=(EditText)findViewById(R.id.input);       insert=(Button)findViewById(R.id.insert);       show=(TextView)findViewById(R.id.show);        uri=uri.parse(AUTHORITY);        cr=this.getContentResolver();        insert.setOnClickListener(new Button.OnClickListener(){@Overridepublic void onClick(View v) {// TODO Auto-generated method stub ContentValues values=new ContentValues();        values.put("name", input.getText().toString());        cr.insert(uri, values);        Cursor c=cr.query(uri, null, null, null, null);        show.setText("");        c.moveToFirst();        while(c.moveToNext()){         show.append(c.getString(1)+"\r\n");        }        input.setText("");}});           }}