title: Proper method for setting childAspectRatio in flutter
body: <p>What is the proper way of calculating <strong>childAspectRatio</strong> of <strong>SliverGridDelegateWithFixedCrossAxisCount</strong> in flutter. How to manage the the correct height of each view that is compatible with all devices and should work in landscape and portrait</p>
  
  <pre><code>GridView.builder(
      physics: BouncingScrollPhysics(),
      padding: const EdgeInsets.all(4.0),
      itemCount: snapshot.data.results.length,
      gridDelegate: new SliverGridDelegateWithFixedCrossAxisCount(
        crossAxisCount: itemCount,
        childAspectRatio: 0.501,
        mainAxisSpacing: 4.0,
        crossAxisSpacing: 4.0,
      ),
      itemBuilder: (BuildContext context, int index) {
        return GridTile(
            child: _buildGridItem(context, snapshot.data.results[index]));
      });
  </code></pre>