Why when I create a new activity, "setContentView" not recognize my layout?

Question

I just created a new activity (project-> new-> android activity) and I get an error where the R file, which does not recognize the layout created by the activity. I use Ubuntu 13.10 (64 bits)

public class OrderKaraokeActivity extends SherlockActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_order_karaoke);
    }
}

activity_order_karaoke:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".OrderKaraokeActivity" >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />

</RelativeLayout>

Console:

Description Resource    Path    Location    Type
activity_order_karaoke cannot be resolved or is not a field OrderKaraokeActivity.java   /src/com/example/adicionalesprueba  line 18 Java Problem

Import:

Console problem:

Answer 1

remove the following

import com.twable.R;
import com.twable.R.layout;
import com.twable.R.menu;

and include import com.example.adicionalesprueba.R

----

Check your package explorer (the left pane of eclipse), open the gen folder of your project, open the package of your project, You should see a R.java file. If you do not, you're R file is not being generated. Try to clean your project, Project --> Clean. If the file is still not there, then you're R file is not being built. This can happen for many reasons. A very common one is that one of your XML files is not properly structured