unity3d导出android工程二次开发图标问题

Question

最近在用unity做一些开发，今天发现直接将unity导出成android工程然后直接运行，图标可以正常显示，manifest部分代码如下

Java code?

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<application         android:icon="@drawable/app_icon"         android:label="@string/app_name">         <activity             android:name="com.easyar.hellounity.UnityPlayerActivity"             android:configChanges="mcc|mnc|locale|touchscreen|keyboard|keyboardHidden|navigation|orientation|screenLayout|uiMode|screenSize|smallestScreenSize|fontScale|layoutDirection"             android:label="@string/app_name"             android:launchMode="singleTask"             android:screenOrientation="portrait">             <intent-filter>                 <action android:name="android.intent.action.MAIN" />                 <category android:name="android.intent.category.LAUNCHER" />             </intent-filter>         </activity>     </application>

可以想在此基础上做二次开发，创建MainActivity继承UnityPlayerActivity，修改manifest代码如下:

Java code?

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<application         android:icon="@drawable/app_icon"         android:label="@string/app_name">         <activity             android:name="com.easyar.hellounity.MainActivity"             android:configChanges="mcc|mnc|locale|touchscreen|keyboard|keyboardHidden|navigation|orientation|screenLayout|uiMode|screenSize|smallestScreenSize|fontScale|layoutDirection"             android:label="@string/app_name"             android:launchMode="singleTask"             android:screenOrientation="portrait">             <intent-filter>                 <action android:name="android.intent.action.MAIN" />                 <category android:name="android.intent.category.LAUNCHER" />             </intent-filter>         </activity>     </application>

就改了一下启动的activity，app可以正常运行，可以图标就消失了，只要一退出就无法通过图标进入。
请问一下大家这是啥原因？