could not identify launch activity 3a default activity not found

1<activity
2    android:name=".MainActivity"
3    android:label="YourAppName"
4    android:theme="@style/AppTheme.NoActionBar" >
5      <intent-filter>
6            <action android:name="android.intent.action.MAIN" />
7
8            <category android:name="android.intent.category.LAUNCHER" />
9      </intent-filter>
10</activity>
11