Android: volání metody v fragmentu – Java – Fórum – Programujte.com

Jedinou mnou známou možností jak něco změnit něco v fragmentu, je mít v něm metodu, která to vykoná. Už jsem snad prozkoušel všechny možností, abych jí zavolal. Chtěl bych změnit TextView guest_name_id.

MainActivity 

@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		Init();
		
		//Set default fragment.
		fragmentTransaction = fragmentManager.beginTransaction();	//Start of transaction.
			Fragment defaultFragment=new DefaultFragment();
			fragmentTransaction.add(R.id.content_layout, defaultFragment);	// add fragment to layout.
			defaultFragment=null;
		fragmentTransaction.commit();	//end of transaction.
		
		
		//Listener for NameList (ListView). The listener change fragments on screen.
		NameList.setOnItemClickListener(new AdapterView.OnItemClickListener() {
	        @Override
	        public void onItemClick(AdapterView<?> arg0, View view, int position, long id) {
	        	
	        	final String TAG="tag";
	        	
	        	fragmentTransaction = fragmentManager.beginTransaction();	//Start of transaction.
	        		fragmentTransaction.replace(R.id.content_layout, new GuestFragment(), TAG);
	        		fragmentTransaction.addToBackStack(null);	 //add fragment tag (id) for latest editing.  	
				fragmentTransaction.commit(); //end of transaction.
					
				GuestFragment gf= (GuestFragment)getFragmentManager().findFragmentByTag(TAG);

				gf.setName("SDsd");
	        	
	        
	
	        	
	        }
	    });

 fragment class

import android.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ListView;
import android.widget.TextView;

public class GuestFragment extends Fragment {
	
	private TextView nameTextView;
	private ListView orderListView;
	

	public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){
		View view=inflater.inflate(R.layout.guest, container, false);	//create fragment from XML file
				
		nameTextView=(TextView) view.findViewById(R.id.guest_name_id);
		return view;
	}
	
	public void setName(String name){
		nameTextView.setText(name);
	}
}

Edit: Error, který jsem objevil je, že  "gf" je null.