title: Android - RadioButton isn't uncheck with initial checked state
body: <p>I have a RadioButton within a RadioGroup, </p>
  
  <p>the problem arises when i set the initial state of the button</p>
  
  <blockquote>
    <p>android:checked = "true"</p>
  </blockquote>
  
  <p>because if I press the RadioButton "F" the RadioButton "M" doesn't uncheck... </p>
  
  <p>how can I do? what is wrong? </p>
  
  <p>here's the code:</p>
  
  <pre><code>&lt;RadioGroup
     android:id="@+id/registrazione_utente_sesso"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:orientation="horizontal" &gt;
  
     &lt;RadioButton
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:checked="true"
        android:text="M"
        android:textColor="#ff7415"
        android:textSize="18sp" /&gt;
  
     &lt;RadioButton
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="13.33dp"
        android:text="F"
        android:textColor="#ff7415"
        android:textSize="18sp" /&gt;
  &lt;/RadioGroup&gt;
  </code></pre>
  
  <p>screen:</p>
  
  <p>initial state (correct):</p>
  
  <p><a href="http://i.imgur.com/YsUIg.png" rel="nofollow">http://i.imgur.com/YsUIg.png</a></p>
  
  <p>final state when i press RadioButton "F" (wrong):</p>
  
  <p><a href="http://i.imgur.com/YJms9.png" rel="nofollow">http://i.imgur.com/YJms9.png</a></p>
  
  <p>thanks</p>