Implement existing Activity(within there extends/implements) in Fragments (Sherlock) - android-activity

Question

I have developed an app with some activities. Now I would implenent a Navigation with fragments and Sherlock.
I found a lot of examples, but I don't know how to implement my exiting activities.
Since 3 days I'm looking for an solution...
So it would be great if someone can give me a solution or hint.
Thank you!
These are fragment files:
MainActivity
import android.content.Context;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentTransaction;
import com.actionbarsherlock.app.ActionBar;
import com.actionbarsherlock.app.ActionBar.Tab;
import com.actionbarsherlock.app.SherlockFragmentActivity;
public class MainActivity extends SherlockFragmentActivity {
public static Context appContext;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
//ActionBar gets initiated
ActionBar actionbar = getSupportActionBar();
//Tell the ActionBar we want to use Tabs.
actionbar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
//initiating both tabs and set text to it.
ActionBar.Tab PlayerTab = actionbar.newTab().setText("Fragment A");
ActionBar.Tab StationsTab = actionbar.newTab().setText("Fragment B");
//create the two fragments we want to use for display content
Fragment PlayerFragment = new AFragment();
Fragment StationsFragment = new BFragment();
//set the Tab listener. Now we can listen for clicks.
PlayerTab.setTabListener(new MyTabsListener(PlayerFragment));
StationsTab.setTabListener(new MyTabsListener(StationsFragment));
//add the two tabs to the actionbar
actionbar.addTab(PlayerTab);
actionbar.addTab(StationsTab);
}
class MyTabsListener implements ActionBar.TabListener {
public Fragment fragment;
public MyTabsListener(Fragment fragment) {
this.fragment = fragment;
}
#Override
public void onTabReselected(Tab tab, FragmentTransaction ft) {
//Toast.makeText(MainActivity.appContext, "Reselected!", Toast.LENGTH_LONG).show();
}
#Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
ft.replace(R.id.fragment_container, fragment);
}
#Override
public void onTabUnselected(Tab tab, FragmentTransaction ft) {
ft.remove(fragment);
}
}
}
AFragment
import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
public class AFragment extends Fragment {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.afragment, container, false);
}
}
BFragment
import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
public class BFragment extends Fragment {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.bfragment, container, false);
}
}
And here is an exiting Activity
import java.text.SimpleDateFormat;
import java.util.Date;
import android.app.Activity;
import android.content.Intent;
import android.database.Cursor;
import android.graphics.Color;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
public class Admin_Activity extends Activity implements OnClickListener {
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.admin);
//Something else
//Database / Cursor actions
//...
//Listener Button
Button button_xy = (Button) this.findViewById(R.id.button_xy);
button_xy.setOnClickListener(this);
//...
public void onClick(View v) {
switch(v.getId()) {
case R.id.buttonxy:
//intent...
break;
}
}
}