title: Visibility of ProgressBar
body: <p>I need to process some data when the user click the button in one activity, so the screen looks like the app stops for 2-3 seconds. It isn't a lot but I want to give the user information that everything is ok and IMO the best way will be the progressbar which is visible only when data are processed. </p>
  
  <p>I found the code of ProgressBar and it looks like this:</p>
  
  <pre><code>    &lt;ProgressBar
      android:id="@+id/loadingdata_progress"
      style="?android:attr/progressBarStyle"
      android:layout_width="50dp"
      android:layout_height="50dp"
      android:layout_alignBottom="@+id/fin2_note"
      android:layout_centerHorizontal="true"
      android:indeterminate="true"
      android:visibility="invisible" /&gt;
  </code></pre>
  
  <p>and inserted it on the middle of my layout.</p>
  
  <p>And to try if the progressbar works, I put this code </p>
  
  <p><code>loadingimage= (ProgressBar) findViewById(R.id.loadingdata_progress);
          loadingimage.setVisibility(View.VISIBLE);
  </code></p>
  
  <p>into <code>onCreate</code> method and everything looks fine. 
  Then I recreated the code to show this progressbar only if the data is processed. </p>
  
  <p>After click the user invoke this method </p>
  
  <pre><code>   public void fin2_clickOnFinalization(View v)
     {    
  
              loadingimage= (ProgressBar) findViewById(R.id.loadingdata_progress);
      loadingimage.setVisibility(View.VISIBLE);
  
            // code where data is processing
              loadingimage.setVisibility(View.INVISIBLE);
         }
  </code></pre>
  
  <p>and nothing appear on the screen. I don't know where is the mistake. If I found the progress bar by id, It's strange for me that I can control it in onCreate method but in onclick method it's out of my control.   </p>