ContentObserver类的使用

application A提供了provider, application B可以使用.

application on更新provider后, 要通知application B, 而application B通过ContentObserver获取更新状态.

要在application A中设置访问权限, 并更新

在application A中的AndroidManifest.xml中, 设置provider权限

<application>    <provider android:name="AProvider">        <path-permissionandroid:readPermission="android.permission.READ_EXTERNAL_STORAGE"android:writePermission="android.permission.WRITE_EXTERNAL_STORAGTE" /></application>

在application A中, provider中添加

public class AProvider extends ContentProvider {    public update(uri, ...) {        // do some work        getContext().getContentProvider().notifyChange(uri, null);    }}

application B通过ContentOberver获取更新消息

包括获取权限和设置ContentObserver.

获取权限

首先, application B使用application A的provider, 要在application B中的AndroidManifest.xml中, 获取provider权限. 写权限包含了读权限, 所以可以不用写读权限.

    <uses-premission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>    <uses-premission android:name="android.permission.READ_EXTERNAL_STORAGE"/>

设置ContentObserver

有两种使用ContentObserver的方法.

方法1: 在cursor中调用cursor.registerContentObserver, 不需要handler传递消息

在onCreate()中使用cursor.registerContentObserver, new一个Observer, 重写onChange()
这种方法比较简单 代码如下:

import android.database.Cursor;import android.database.ContentObserver;import android.provider.MediaStore;public class BActivity extends Activity {    private Cursor mCursor;    public onCreate() {        mCursor = null;        ContentProvider resolver = getContentResolver();        try {mCursor = resolver.query(uri, new String[] {MediaStore.Files.FileColumns._ID}, null, null, null);mCursor.registerContentObserver(new ContentObserver(null) {        @Override        public void onChange(boolean selfChange) {// do some work when obsering some changes        }    });        } catch (Exception e) {//TODO: handle exceptione.printStackTrace();        }    }    public onDestroy() {        if (mCursor != null && mCursor.isClosed()) {mCursor.close();mCursor = null;        }    }}

方法2: 重写ContentObserver, 并使用handler来传递消息

• 1 创建特定的ContentObserver派生类, 重载父类构造方法, 重载onChange()方法处理回调后的功能实现

• 2 利用context.getContentResolver()获得ContentResovler对象, 调用registerContentObserver()方法注册

• 3 ContentObserver的生命周期不同步于Activity和Service等, 在不需要时, 需要手动调用unregisterContentObserver()取消注册

重载ContentProvider

public class TwoContentObserver extends ContentObserver {    private static String TAG = "TwoContentObserver";        private static int MSG_ONE_PROVIDER_CHANGE = 1;        private Context mContext;    private Handler mHandler;   // use handler to update UI thread        public TwoContentObserver(Context context, Handler handler) {        super(handler);        mContext = context;        mHandler = handler;    }        @Overrride    public void onChange(boolean selfChange) {        Log.i(TAG, "--------TwoContentObserver change--------");    Uri outUri = Uri.parse("");        Cursor cursor = mContext.getContentResolver().query(outUri, null, null, null, null);        if (c != null ) {StringBuilder stringBuilder = new StringBuilder();while (cursor.moveToNext()) {    // do some work}        }        cursor.close();        mHandler.obtainMessage(MSG_ONE_PROVIDER_CHANGE, sb.toString().sendToTarget());    }}

在Activity调用

public class MainActivity extends Activity {    private static final int MSG_ONE_PROVIDER_CHANGE = 1;    private TwoContentObserver twoContentObserver;        @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        twoContentObserver = new TwoContentObserver(this, mHandler);        // 注册ContentObserver        registerContentObservers();    }        private void registerContentObservers() {        Uri uri = Uri.parse("");        getContentResovler().registerContentObserver(uri, false, twoContentObserver);    }        private Handler mHanlder = new Handler() {        publc void handlerMessage(Message msg) {switch(msg.what) {    case MSG_ONE_PROVIDER_CHANGE:        // do some work        break;    default:        break;}        }    };        @Override    public void onDestroy() {        super.onDestroy();        // 取消注册        getContentResolver().unregisterContentObserver(twoContentObserver);    }}

参考
http://www.cnblogs.com/slider/archive/2012/02/14/2351702.html