title: Getting NullPointerException on isChecked() for a checkbox in DialogFragment
body: <p>I have a checkbox in a login DialogFragment that I want to use to check to see if I should add the entered user name to the preferences.  But when I do an if using the checkbox's isChecked() method I get a NullPointerException.  I added a try/catch clock and then further tried to add a Log.d of the checkbox's toString output and again the NullPointerException shows up.  So, while it's clear that the code does not seem to recognize the existence of the checkbox in the current scope, I can't figure out what I over looked.  It allowed me to create a CheckBox using the findViewById without error.  Thanks.</p>
  
  <p>source code for login DialogFragment:</p>
  
  <pre><code>public class LoginDialogFragment extends DialogFragment {
  
  
  public interface LoginDialogListener {
      public void onDialogPositiveClick(DialogFragment dialog);
      public void onDialogNegativeClick(DialogFragment dialog);
  }
  
  LoginDialogListener mListener;
  
  public void onAttach(Activity activity) {
      super.onAttach(activity);
      // Verify that the host activity implements the callback interface
      try {
          // Instantiate the NoticeDialogListener so we can send events to the host
          mListener = (LoginDialogListener) activity;
      } catch (ClassCastException e) {
          // The activity doesn't implement the interface, throw exception
          throw new ClassCastException(activity.toString()
                  + " must implement NoticeDialogListener");
      }
  }
  public Dialog onCreateDialog(Bundle savedInstanceState) {
      AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
      // Get the layout inflater
      LayoutInflater inflater = getActivity().getLayoutInflater();
  
      // Inflate and set the layout for the dialog
      // Pass null as the parent view because its going in the dialog layout
      builder.setView(inflater.inflate(R.layout.login_dialog, null))
      // Add action buttons
             .setPositiveButton("Login", new DialogInterface.OnClickListener() {
                 @Override
                 public void onClick(DialogInterface dialog, int id) {
                  // Send the positive button event back to the host activity
                     CheckBox loginCheckBox = 
  (CheckBox)getActivity().findViewById(R.id.input_chkbox);
                     try{
                         if(loginCheckBox.isChecked() == true){
  
  mListener.onDialogPositiveClick(LoginDialogFragment.this);
                         }else{
  
  mListener.onDialogNegativeClick(LoginDialogFragment.this);
                         }
                     }catch(Exception e){
                         Log.d(null, e.toString());
                         Log.d(null, loginCheckBox.toString());  // got 
  nullPointerException again when I added this line in catch block.
                         Toast eToast = Toast.makeText(getActivity(), "error in: 
  LoginDialogFragment.setPosButton.onClick", Toast.LENGTH_LONG);
                         eToast.show();
                     }
                 }
             })    
  </code></pre>
  
  <p>source code for parent activity of the dialog fragment:</p>
  
  <pre><code>public class UsingPreferencesActivity
  extends FragmentActivity
      implements LoginDialogFragment.LoginDialogListener{
  
  protected void onCreate(Bundle savedInstanceState){
      super.onCreate(savedInstanceState);
      this.setContentView(R.layout.main);
      this.showLoginDialog();
  
  }
  
  public void showLoginDialog() {
      // Create an instance of the dialog fragment and show it
      DialogFragment dialog = new LoginDialogFragment();
      dialog.show(getSupportFragmentManager(), "LoginDialogFragment");
  }
  
  public void onDialogPositiveClick(DialogFragment dialog) {
      Toast toast = Toast.makeText(getBaseContext(), "OK", Toast.LENGTH_LONG);
      toast.show();
  
  }
  
  public void onDialogNegativeClick(DialogFragment dialog) {
      Toast toast = Toast.makeText(getBaseContext(), "Cancel", 
  Toast.LENGTH_LONG);
      toast.show();
  }
  
  public void onClickLoad(View view){
      Intent i = new Intent("com.example.homework09.AppPreferenceActivity");
      startActivity(i);
  }
  
  
  public void onClickDisplay(View view){
      SharedPreferences appPrefs = 
  getSharedPreferences("com.example.homework09_preferences",MODE_PRIVATE);
      DisplayText(appPrefs.getString("editTextPref", ""));
  }
  
  
  public void onClickModify(View view){
      SharedPreferences appPrefs = 
  getSharedPreferences("com.example.homework09_preferences", MODE_PRIVATE);
      SharedPreferences.Editor prefsEditor = appPrefs.edit();
      prefsEditor.putString("editTextPref", 
  ((EditText)findViewById(R.id.etNewUsername)).getText().toString());
      prefsEditor.commit();
      DisplayText(appPrefs.getString("editTextPref", ""));
  }
  
  
  public void onClickReset(View view){
  
      SharedPreferences appPrefs = 
  getSharedPreferences("com.example.homework09_preferences", MODE_PRIVATE);
      SharedPreferences.Editor prefsEditor = appPrefs.edit();
      prefsEditor.putString("editTextPref", " ");
      prefsEditor.commit();
      DisplayText(appPrefs.getString("editTextPref", ""));
  }
  
  
  private void DisplayText(String str){
      Toast.makeText(getBaseContext(), str, Toast.LENGTH_LONG).show();
      TextView textView = (TextView)findViewById(R.id.tvUsername);
      textView.setText(str);
  }
  
  }
  </code></pre>
  
  <p>layout for DialogFragment (login_dialog.xml):</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:orientation="vertical" &gt;
  
  
  &lt;EditText 
      android:id="@+id/input"
      android:layout_width="fill_parent"
      android:layout_height="wrap_content"
      android:hint="[Enter username here]"/&gt;
  
  &lt;CheckBox 
      android:id="@+id/input_chkbox"
      android:layout_width="fill_parent"
      android:layout_height="wrap_content"
      android:text="Save Username?"
      android:defaultValue="false"
      /&gt;
  
  &lt;/LinearLayout&gt;
  </code></pre>