来电的广播接收器不工作？

<uses-permission android:name="android.permission.READ_PHONE_STATE" />

<receiver android:name=".MyBroadcastReceiver">
    <intent-filter>
        <action android:name="android.intent.action.PHONE_STATE" />
    </intent-filter>
</receiver>

public class MyBroadcastReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();
        if (action.equals(TelephonyManager.ACTION_PHONE_STATE_CHANGED)) {
            String state = intent.getStringExtra(TelephonyManager.EXTRA_STATE);
            if (state.equals(TelephonyManager.EXTRA_STATE_RINGING)) {
                // 处理来电事件
            }
        }
    }
}