ContentObserver類的使用

ContentObserver類的使用

application A提供了provider, application B能夠使用.

application on更新provider後, 要通知application B, 而application B經過ContentObserver獲取更新狀態.

要在application A中設置訪問權限, 並更新

在application A中的AndroidManifest.xml中, 設置provider權限

<application>
    <provider android:name="AProvider">
        <path-permission
            android: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經過ContentOberver獲取更新消息

包括獲取權限和設置ContentObserver.

獲取權限

首先, application B使用application A的provider, 要在application B中的AndroidManifest.xml中, 獲取provider權限. 寫權限包含了讀權限, 因此能夠不用寫讀權限.

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

設置ContentObserver

有兩種使用ContentObserver的方法.

方法1: 在cursor中調用cursor.registerContentObserver, 不須要handler傳遞消息

在onCreate()中使用cursor.registerContentObserver, new一個Observer, 重寫onChange()
這種方法比較簡單 代碼以下:

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 exception
            e.printStackTrace();
        }
    }

    public onDestroy() {
        if (mCursor != null && mCursor.isClosed()) {
            mCursor.close();
            mCursor = null;
        }
    }
}

方法2: 重寫ContentObserver, 並使用handler來傳遞消息

• 1 建立特定的ContentObserver派生類, 重載父類構造方法, 重載onChange()方法處理回調後的功能實現

• 2 利用context.getContentResolver()得到ContentResovler對象, 調用registerContentObserver()方法註冊

• 3 ContentObserver的生命週期不一樣步於Activity和Service等, 在不須要時, 須要手動調用unregisterContentObserver()取消註冊

重載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調用

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);
        // 註冊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();
        // 取消註冊
        getContentResolver().unregisterContentObserver(twoContentObserver);
    }
}

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