title: RadioGroup retrieve is null
body: <p>I try to retrieve my RADIOGROUP for check which Radio Button is checked. For this, I use this code in onCreate() :</p>
  
  <pre><code>/**
   * @param savedInstanceState
   */
  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
  
  
      radioGroup_LANGUE = (RadioGroup) findViewById(R.id.RadioGroup_LANGUE);
      radioGroup_MODE = (RadioGroup) findViewById(R.id.RGroup_ModeConnexion);
  ... }
  </code></pre>
  
  <p><strong>But I use the debug, and AndroidStudio tell me radioGroup_LANGUE is null. So I get NULLPOINTER EXCEPTION</strong>.</p>
  
  <p>In my alertdialog, when user click on OK Button :</p>
  
  <pre><code>.setNegativeButton("OK", new DialogInterface.OnClickListener() {
                  public void onClick(DialogInterface dialog, int id) {
                      // if this button is clicked, just close
                      // the dialog box and do nothing
                      radioGroup_LANGUE.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
                          public void onCheckedChanged(RadioGroup radioGroup_LANGUE, int checkedId) {
                              // This will get the radiobutton that has changed in its check state
                              RadioButton checkedRadioButton = (RadioButton)radioGroup_LANGUE.findViewById(checkedId);
  
                              // This puts the value (true/false) into the variable
                              boolean isChecked = checkedRadioButton.isChecked();
  
                              /// If the radiobutton that has changed in check state is now checked...
                              if (isChecked)
                              {
                                  // Changes the textview's text to "Checked: example radiobutton text"
                                  Toast.makeText(MainActivity.this,"Checked:" + checkedRadioButton.getText(),Toast.LENGTH_LONG).show();
                              }
                       }
                      });
                  }});
  </code></pre>
  
  <p>My xml :</p>
  
  <pre><code>&lt;RadioGroup
      android:layout_width="148dp"
      android:layout_height="wrap_content"
      android:layout_gravity="center_horizontal"
      android:id="@+id/RadioGroup_LANGUE"&gt;
  
  &lt;RadioButton
          android:layout_width="137dp"
          android:layout_height="wrap_content"
          android:text="@string/Langue_1"
          android:id="@+id/BouttonRADIO_EN"
          android:layout_gravity="center_horizontal"
          android:textSize="20dp"
          android:textStyle="bold" /&gt;
  
  &lt;RadioButton
          android:layout_width="137dp"
          android:layout_height="wrap_content"
          android:text="@string/Langue_2"
          android:id="@+id/BouttonRADIO_FR"
          android:layout_gravity="center_horizontal"
          android:textSize="20dp"
          android:textStyle="bold" /&gt;
  
  &lt;/RadioGroup&gt;
  </code></pre>
  
  <p>Error log :</p>
  
  <pre><code>06-01 22:51:53.053 21336-21336/com.example.my020571.sterela2 E/AndroidRuntime: FATAL EXCEPTION: main
  Process: com.example.my020571.sterela2, PID: 21336
  java.lang.NullPointerException
     at com.example.my020571.sterela2.MainActivity$4.onClick(MainActivity.java:321)
     at com.android.internal.app.AlertController$ButtonHandler.handleMessage(AlertController.java:170)
     at android.os.Handler.dispatchMessage(Handler.java:102)
     at android.os.Looper.loop(Looper.java:146)
     at android.app.ActivityThread.main(ActivityThread.java:5598)
     at java.lang.reflect.Method.invokeNative(Native Method)
     at java.lang.reflect.Method.invoke(Method.java:515)
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1283)
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099)
     at dalvik.system.NativeStart.main(Native Method)
  </code></pre>
  
  <p>LINE 321 :</p>
  
  <pre><code>int selectedID = rGroup_LANGUE.getCheckedRadioButtonId();
  </code></pre>
  
  <p>METHOD :</p>
  
  <pre><code>private void changerLangue() {
  
      AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(
              context);
  
  
      final View view = View.inflate(MainActivity.this, R.layout.changer_langue, null);
  
  
      alertDialogBuilder.setView(view);
  
  
  
      // Titre de la fenêtre
      alertDialogBuilder.setTitle("Langue");
      // set dialog message
      alertDialogBuilder
              .setMessage("Veuillez choisir votre langue :")
              .setCancelable(false)
              .setIcon(R.drawable.logo_langue)
  
              .setPositiveButton("ANNULER", new DialogInterface.OnClickListener() {
                  public void onClick(DialogInterface dialog, int id) {
                      // if this button is clicked, close
                      // current activity
                      dialog.cancel();
                  }
              })
              .setNegativeButton("OK", new DialogInterface.OnClickListener() {
                  public void onClick(DialogInterface dialog, int id) {
                      // if this button is clicked, just close
                      // the dialog box and do nothing
                      int selectedID = rGroup_LANGUE.getCheckedRadioButtonId();
                      RadioButton selectedRadioButton = (RadioButton)findViewById(selectedID);
                      Toast.makeText(getApplicationContext(),selectedRadioButton.getText().toString(),Toast.LENGTH_SHORT).show();
                  }});
  
  
                              // create alert dialog
      AlertDialog alertDialog = alertDialogBuilder.create();
  
      // show it
      alertDialog.show();
  }
  </code></pre>