title: Android when use PreferenceCategory and when PreferenceScreen
body: <p>I am learning about android but i do not understand the difference between PreferenceCategory and PreferenceScreen, i saw that many tutorial used the second one instead the first one, but i do not understand why.
  When you recommend me to use the first one instead the second or vice versa.
  Another thing, does these two codes made the same thing?</p>
  
  <pre><code>&lt;PreferenceCategory
      android:title="first"&gt;
      &lt;CheckBoxPreference
          android:key="first_preferences"
          android:title="first"
          android:defaultValue="false" /&gt;`
  &lt;/PreferenceCategory&gt;
  </code></pre>
  
  <p>and the second code:</p>
  
  <pre><code>&lt;PreferenceScreen
      android:title="second"&gt;
      &lt;CheckBoxPreference
          android:key="second_preferences"
          android:title="second"
          android:defaultValue="false" /&gt;`
  &lt;/PreferenceScreen&gt;
  </code></pre>
  
  <p>thanks for the help.</p>