title: Android: why should IDs of views should be positive numbers?
body: <p>In View.java, </p>
  
  <p>setId - "Sets the identifier for this view. The identifier does not have to be unique in this view's hierarchy. The identifier should be a positive number."</p>
  
  <p>&amp;</p>
  
  <p>findViewById - "Look for a child view with the given id. If this view has the given id,</p>
  
  <p>Why I could not use a negative number as the id of the view? I commented out the </p>
  
  <pre><code>    public final View findViewById(int id) {
      // The original android check at here
      //  if (id &lt; 0) { 
      // is commented out to test if system could run when Ids are negative numbers
      if (id == NO_ID) {
          return null;
      }
      return findViewTraversal(id);
  }
  </code></pre>
  
  <p>The system seems to be working fine. </p>