title: Execution failed for task ':app:mergeDebugResources'. > -1
body: <p>I'm new in android and i have this error, i've been trying looking everywhere for the solution and still don't know how to solve this. I have this :</p>
  
  <blockquote>
    <p>Error:Execution failed for task ':app:mergeDebugResources'.> -1</p>
  </blockquote>
  
  <p>and the effect is every R in my activities got "cannot resolve symbol R"</p>
  
  <p>i've been trying to clean, build and sync with gradle but still not working..</p>
  
  <p>this is my resources:
  strings.xml</p>
  
  
  
  <pre><code>&lt;resources&gt;
      &lt;string name="app_name"&gt;mLibrary AeU&lt;/string&gt;
      &lt;string name="action_search"&gt;action_search&lt;/string&gt;
      &lt;string name="search_hint"&gt;search_hint&lt;/string&gt;
      &lt;string name="welcome"&gt;welcome&lt;/string&gt;
      &lt;string name="btn_logout"&gt;btn_logout&lt;/string&gt;
  &lt;/resources&gt;
  </code></pre>
  
  <p>colors.xml</p>
  
  <pre><code>    &lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;resources&gt;
      &lt;color name="colorPrimary"&gt;#2f2d79&lt;/color&gt;
      &lt;color name="colorPrimaryDark"&gt;#303F9F&lt;/color&gt;
      &lt;color name="colorAccent"&gt;#FF4081&lt;/color&gt;
  
      &lt;color name="callNumber"&gt;#666666&lt;/color&gt;
      &lt;color name="author_and_year"&gt;#888888&lt;/color&gt;
      &lt;color name="list_divider"&gt;#d9d9d9&lt;/color&gt;
      &lt;color name="list_row_start_color"&gt;#ffffff&lt;/color&gt;
      &lt;color name="list_row_end_color"&gt;#ffffff&lt;/color&gt;
      &lt;color name="list_row_hover_start_color"&gt;#ebeef0&lt;/color&gt;
      &lt;color name="list_row_hover_end_color"&gt;#ebeef0&lt;/color&gt;
  &lt;/resources&gt;
  </code></pre>
  
  <p>dimens.xml</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;resources&gt;
      &lt;!-- Default screen margins, per the Android Design guidelines. --&gt;
      &lt;dimen name="activity_horizontal_margin"&gt;16dp&lt;/dimen&gt;
      &lt;dimen name="activity_vertical_margin"&gt;16dp&lt;/dimen&gt;
  
      &lt;dimen name="title"&gt;17dp&lt;/dimen&gt;
      &lt;dimen name="author"&gt;15dip&lt;/dimen&gt;
      &lt;dimen name="callNumber"&gt;13dip&lt;/dimen&gt;
      &lt;dimen name="year"&gt;13dip&lt;/dimen&gt;
  &lt;/resources&gt;
  </code></pre>
  
  <p>styles.xml</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;resources&gt;
      &lt;!-- Base application theme. --&gt;
      &lt;style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar"&gt;
          &lt;!-- Customize your theme here. --&gt;
          &lt;item name="colorPrimary"&gt;@color/colorPrimary&lt;/item&gt;
          &lt;item name="colorPrimaryDark"&gt;@color/colorPrimaryDark&lt;/item&gt;
          &lt;item name="colorAccent"&gt;@color/colorAccent&lt;/item&gt;
      &lt;/style&gt;
  
  &lt;/resources&gt;
  </code></pre>
  
  <p>I need your help.</p>