title: Show widget at the center bottom on a gridview
body: <p>I have a gridview with 2/3 columns and I would like to show a loading indicator at the bottom-center of the grid when the user scrolls to the end. Adding the loading indicator as the last element of the grid doesn't look good because it isn't centered. Is this possible?</p>
  
  <p>Code snippet:</p>
  
  <pre><code>GridView.builder(
    gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
        crossAxisCount: 2, childAspectRatio: 480 / 315),
    controller: controller,
    itemCount: videos.length + 1,
    itemBuilder: (context, index) {
      if (index == videos.length) {
        //show loading indicator at last index
        return SpinKitThreeBounce(
                 color: Colors.white,
                 size: 35.0,
              );
      }
      return VideoItem(video: videos[index]);
    },
  );
  </code></pre>
  
  <p>What I have:</p>
  
  <p><a href="https://i.stack.imgur.com/Yg719.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Yg719.png" alt="enter image description here"></a></p>
  
  <p>What I want:</p>
  
  <p><a href="https://i.stack.imgur.com/lkpwe.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/lkpwe.png" alt="enter image description here"></a></p>