Question

I have this main activity

public class MainActivity extends FragmentActivity {

SectionsPagerAdapter mSectionsPagerAdapter;


ViewPager mViewPager;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);


    // Create the adapter that will return a fragment for each of the three
    // primary sections of the app
    mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());

    // Set up the ViewPager with the sections adapter.
    mViewPager = (ViewPager) findViewById(R.id.pager);
    mViewPager.setAdapter(mSectionsPagerAdapter);

}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.activity_main, menu);  
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle item selection
    switch (item.getItemId()) {
        case R.id.menu_settings4:
            mainactivity();
            return true;
        case R.id.menu_settings1:
            ipallilos();
            return true;
        case R.id.menu_settings2:
            rithmisi();
            return true;
        case R.id.menu_settings3:
            sxetika();
            return true;

        default:
            return super.onOptionsItemSelected(item);
    }

}

private void mainactivity() {

    Toast.makeText(MainActivity.this, "Επιστροφή στην Αρχική Σελίδα", 
            Toast.LENGTH_SHORT).show();
}
private void rithmisi() {
    setContentView(R.layout.rithmisis);
    Toast.makeText(MainActivity.this, "Loading Settings", 
            Toast.LENGTH_SHORT).show();
}

private void ipallilos() {
    setContentView(R.layout.ipallilos);
    Toast.makeText(MainActivity.this, "Loading Staff", 
            Toast.LENGTH_SHORT).show();
}

private void sxetika() {
    //anoigma menou efarmogis
    setContentView(R.layout.sxetikame);
    Toast.makeText(MainActivity.this, "Loading about Software", 
            Toast.LENGTH_SHORT).show();


}

 @Override
 public boolean onKeyDown(int keyCode, KeyEvent event)  {
     if ((keyCode == KeyEvent.KEYCODE_BACK)) {
         //moveTaskToBack(true);
         super.onBackPressed();
         return true;
     }

     return super.onKeyDown(keyCode, event);
 }




public class SectionsPagerAdapter extends FragmentPagerAdapter {

    public SectionsPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        // getItem is called to instantiate the fragment for the given page.
        // Return a DummySectionFragment (defined as a static inner class
        // below) with the page number as its lone argument.
        Fragment fragment = new DummySectionFragment();
        Bundle args = new Bundle();
        args.putInt(DummySectionFragment.ARG_SECTION_NUMBER, position + 1);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public int getCount() {
        // Show 3 total pages.
        return 2;
    }


    @Override
    public CharSequence getPageTitle(int position) {
        switch (position) {
            case 0:
                return getString(R.string.title_section1).toUpperCase();
           // case 1:
              //  return getString(R.string.title_section2).toUpperCase();
            case 1:
                return getString(R.string.title_section3).toUpperCase();
        }
        return null;
    }
}


public static class DummySectionFragment extends Fragment {
    public DummySectionFragment() {
    }
    public static final String ARG_SECTION_NUMBER = "section_number";



    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {

        Bundle args = getArguments();
        switch (args.getInt(ARG_SECTION_NUMBER)){

        case 1: 
            return inflater.inflate(R.layout.paraggeleialayout, container, false);


        case 2:
             return inflater.inflate(R.layout.trapezia, container, false);

    }

        return getView();

}





    }
}

I have at .paraggeleialayout some buttons.
I have try to add setOnClickListener to my button to open an other class but it does not
work. Here is my paraggeleia class.

public class paraggeleia extends Activity {

 @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
           setContentView(R.layout.paraggeleialayout);
              TextView text = (TextView) findViewById(R.id.TextView1);
                 Button bTutorial = (Button) findViewById(R.id.button51);
                text.setText(R.string.paraggeleia);
           bTutorial.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v){
             finish();
            }
        });
    }





    @Override
     public boolean onKeyDown(int keyCode, KeyEvent event)  {
         if ((keyCode == KeyEvent.KEYCODE_BACK)) {
             super.onBackPressed();
             return true;
         }

         return super.onKeyDown(keyCode, event);
     }
}

Answer 1

Alright, I think this is clearer now, so you want your ViewPager layout to launch the next Activity. You may want to do something like this:

case 1: 
       View v = inflater.inflate(R.layout.paraggeleialayout, container, false);
       Button bTutorial = (Button) v.findViewById(R.id.button51);
           bTutorial.setOnClickListener(new View.OnClickListener() {
           public void onClick(View v){
           getActivity().startActivity(new Intent (getActivity(), paraggeleia.class));
            }
        });
return v;

However your paraggeleia.class as it stands contains the same layout (R.layout.paraggeleialayout) as the Fragment, so consider changing that Activity’s layout to something else.