片段交易无法正常工作

在我的FragmnetActivity类中，我有3个fragmnet的Fragmnet事务。但是我的onclick可能无法正常工作。如果条件不满足，它只能工作一个。如果条件不起作用，则我另一个可以工作。

我在这里做错了什么..

public class Indi_Add_Details_menu extends FragmentActivity{

Fragment fragment;
Button btnFragment1, btnFragment2, btnFragment3, btnFragment4;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.add_detal_menu);
    btnFragment1 = (Button)findViewById(R.id.btn1);
    btnFragment2 = (Button)findViewById(R.id.btn2);
    btnFragment3 = (Button)findViewById(R.id.btn3);
    btnFragment4 = (Button)findViewById(R.id.btn4);

    btnFragment1.setBackgroundResource(R.drawable.add_sbutton_pressed);
    btnFragment2.setBackgroundResource(R.drawable.add_tbutton_pressed);
    btnFragment3.setBackgroundResource(R.drawable.add_pbutton_pressed);
    btnFragment4.setBackgroundResource(R.drawable.view_button_pressed);

    // get an instance of FragmentTransaction from your Activity
    FragmentManager fragmentManager = getFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();

    //add a fragment
    Fragment_addStudentDetails myFragment = new Fragment_addStudentDetails();
    fragmentTransaction.add(R.id.myfragment, myFragment);
    fragmentTransaction.commit();

    btnFragment1.setOnClickListener(btnFragmentOnClickListener);
    btnFragment2.setOnClickListener(btnFragmentOnClickListener);
    btnFragment3.setOnClickListener(btnFragmentOnClickListener);
    btnFragment4.setOnClickListener(btnFragmentOnClickListener);
}

Button.OnClickListener btnFragmentOnClickListener = new Button.OnClickListener(){

    @Override
    public void onClick(View v) {

        Fragment newFragment;

        // Create new fragment
        if(v == btnFragment1){
            newFragment = new Fragment_addStudentDetails();

        }if(v == btnFragment2){
            newFragment = new Group_Add_test();

        }else{
            newFragment = new ExpandableListFragment();
        }

        // Create new transaction
        FragmentTransaction transaction = getFragmentManager().beginTransaction();

        // Replace whatever is in the fragment_container view with this fragment,
        // and add the transaction to the back stack
        transaction.replace(R.id.myfragment, newFragment);
        transaction.addToBackStack(null);

        // Commit the transaction
        transaction.commit();
    }};
public void showDatePickerDialog(View v) {
    new DatePickerFragment((EditText) v).show(getFragmentManager(), "datePicker");
}

}

当我添加然后这样的Switch语句时

 switch (v.getId()){
            case R.id.btn1:
                newFragment = new Fragment_addStudentDetails();
                break;
            case R.id.btn2:
                newFragment = new Group_Add_test();
                break;
            case R.id.btn3:
                newFragment = new ExpandableListFragment();
                break;
            default:
                break;
        }

logcat说，

  Error:(80, 50) error: variable newFragment might not have been initialized