Android : Xamarin Android - fragment controls not being shown in actvitiy

i am trying to call a new activity from a fragment. I have a button at the toolbar, and when it is pressed the following code is being called (this event is inside the fragment):

 Intent secondactitvity = new Intent(this.Activity,typeof(Activity_SecondActivity));
 StartActivity(secondactitvity );

Now the new activity is being called, and here is my code inside OnCreate of the new activity

RequestWindowFeature(WindowFeatures.ActionBar);
ActionBar.SetIcon(Resource.Drawable.icon_toolbar_back_new);


ActionBar.SetCustomView(Resource.Layout.ActionBar_Custom_Layout);
ActionBar.SetDisplayShowCustomEnabled(true);


base.OnCreate(bundle);

SetContentView(Resource.Layout.SecondActivity_Layout);

Here is the SecondActivity_Layout:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<TextView
    android:text="Text"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/textView1" />
<fragment
    class="frag.Fragment_Second"
    android:id="@+id/fragment_secondActivity"
    android:paddingTop="10dip"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" />
 </LinearLayout>

Here is the layout for the fragment:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:minWidth="25px"
android:minHeight="25px">
<TextView
    android:text="@string/secondFragment_name"
    android:textAppearance="?android:attr/textAppearanceMedium"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/textView1" />
<EditText
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/editText1"
    android:paddingLeft="10dp" />
</LinearLayout>

And here is the fragment code:

 public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle      savedInstanceState)
    {

        return inflater.Inflate(Resource.Layout.Fragment_ProjectDetails, container); //view;// base.OnCreateView(inflater, container, savedInstanceState);

    }

 public override void OnActivityCreated(Bundle savedInstanceState)
    {
        Toast.MakeText(this.Activity, "activity for second fragment created",ToastLength.Short).Show();

        base.OnActivityCreated(savedInstanceState);
    }

Now the problem. The second activity remains empty, it is not being filled with the fragment(but there is not an error message). I would unterstand it if the fragment cannot be found or something like that, but in this case all the functions from the fragment (onCreateView, onActivityCreated...) are being called, and the Toast is also being displayed, but the activity is empty. Then i tried to insert a textview at the top of the fragment inside the second activity layout file, and its being shown but the controls from the fragment remain unvisible. Then i tried to change the fragment associated to the second activity, i changed it to the fragment which is calling the activity, and this one is being properly loaded (i changed it inside the .axml file).

What am i missing here, for me it seems like the second one is not being created propery and thus the controls cannot be displayed (but i may also be wrong) ?