第二部分基本组件---2.2ContentProvider和ContentResolver配合使用

 

ContentProvider其实就是对数据加上一层封装，提供统一的接口来供应用程序来进行访问，例子对之前的数据库利用ContentProvider进行封装（应用程序的数据库只对本应用程序可用和可见，外部应用程序要想调用必须通过ContentProvider进行封装）,封装完毕后利用ContentResolver对象来进行查询，示例代码如下：

public class UIDemo extends ContentProvider    {

 

            int version = 1;

            public final String  DB_NAME= "derekTest.db";

            public final String  TABLE_NAME= "table2";

            private  final String TABLE_ID="_id";

            public final String  TITLE= "title";

            public final String  BODY= "body";

            DBHelper dbh = null;

    

    class DBHelper extends SQLiteOpenHelper

    {

 

   public   DBHelper(Context context, String name, CursorFactory factory,     int version) {

            super(context, name, factory, version);

            // TODO Auto-generated constructor stub

      }

 

      @Override

      public void onCreate(SQLiteDatabase db) {

            // TODO Auto-generated method stub

            String sql = "CREATE TABLE " + TABLE_NAME + " (" + TABLE_ID + " INTEGER PRIMARY KEY, " + TITLE

            + " text not null, " + BODY + " text not null " + ");";

            String sql1 = "insert into "+ TABLE_NAME+" ("+TABLE_ID+", "+TITLE+", "+BODY+") values('1','hellokitty','stronger');";

            String sql2 = "insert into "+ TABLE_NAME+" ("+TABLE_ID+", "+TITLE+", "+BODY+") values('2','micky','weaker');";

             

            db.execSQL(sql);

             db.execSQL(sql1);

             db.execSQL(sql2);

      }

 

      @Override

      public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

            // TODO Auto-generated method stub

           

      }

     

    }

      @Override

      public int delete(Uri uri, String selection, String[] selectionArgs) {

            // TODO Auto-generated method stub

            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

            return null;

      }

 

 

      @Override

      public boolean onCreate() {

       dbh  = new DBHelper(this.getContext(),DB_NAME,null,version);

            return false;

      }

 

 

      @Override

      public Cursor query(Uri uri, String[] projection, String selection,

                  String[] selectionArgs, String sortOrder) {

            // TODO Auto-generated method stub

            SQLiteDatabase sqld=dbh.getReadableDatabase();

            Cursor cursor =sqld.query(TABLE_NAME, new String[]{TABLE_ID,TITLE,BODY}, null, null, null, null, null);

            return cursor;

      }

 

 

      @Override

      public int update(Uri uri, ContentValues values, String selection,

                  String[] selectionArgs) {

            // TODO Auto-generated method stub

            return 0;

      }

       

}

UIDemo类继承ContentProvider类后需要实现其抽象方法即公布给外部的接口方法，在这里实现了query的方法

在activity中进行显示的时候：

public final String DB_AUTHORITY ="com.derek.xie.derekTest";

public final Uri DB_URI = Uri.parse("content://" + DB_AUTHORITY + "/table2");

上为自定义好的URI，authority需与manifest文件中对应

<provider android:name="com.derek.xie.UIDemo" 

      android:authorities="com.derek.xie.derekTest">  

      </provider>

注意manifest文件中添加（在application标签里） 

Cursor cursor = this.getContentResolver().query(DB_URI,  new String[]{TITLE,BODY}, null, null, null);

 ListView ls = (ListView)this.findViewById(R.id.listview1);

 SimpleCursorAdapter sca = new SimpleCursorAdapter(this,android.R.layout.simple_list_item_2,cursor,new String[]{TITLE ,BODY},new int[]{android.R.id.text1,android.R.id.text2 });

 ls.setAdapter(sca);

首先利用getContentResolver()得到ContentResolver对象，调用Query方法传入定义好的URI,和需要的列的数据和查询条件返回Cursor对象

Tips:contentResolver和ContentProvider之间的关系非常简单，通过查看android源码，

ContentResolver类中的query方法可看到：

public final Cursor query(Uri uri, String[] projection,

            String selection, String[] selectionArgs, String sortOrder) {

        IContentProvider provider = acquireProvider(uri);

        if (provider == null) {

            return null;

        }

 ……

            Cursor qCursor = provider.query(uri, projection, selection, selectionArgs, sortOrder);

   …  …        

}

Query方法实际上会先通过uri获得provider对象然后,调用我们自己实现的ContentProvider抽象类里面的query方法