title: How to support `layout_columnWeight` and `layout_rowWeight` in pre API 21?
body: <p>I use the below grid layout with <code>layout_columnWeight</code> and <code>layout_rowWeight</code> to centralize my view in the grid cell.</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:tools="http://schemas.android.com/tools"
  android:id="@+id/activity_main"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  &gt;
  
  &lt;GridLayout
      android:id="@+id/container_grid"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:columnCount="2"
      android:rowCount="3"
      android:orientation="horizontal"&gt;
  
      &lt;View
          android:id="@+id/view_red"
          android:layout_height="100dp"
          android:layout_width="100dp"
          android:layout_columnWeight="1"
          android:layout_rowWeight="1"
          android:layout_gravity="center"
          android:background="#ff0000"
          android:layout_row="0"
          android:layout_column="0" /&gt;
  
      &lt;View
          android:id="@+id/view_green"
          android:layout_height="100dp"
          android:layout_width="100dp"
          android:layout_columnWeight="1"
          android:layout_rowWeight="1"
          android:layout_gravity="center"
          android:background="#00ff00"
          android:layout_row="0"
          android:layout_column="0" /&gt;
  
      &lt;View
          android:id="@+id/view_blue"
          android:layout_height="100dp"
          android:layout_width="100dp"
          android:layout_columnWeight="1"
          android:layout_rowWeight="1"
          android:layout_gravity="center"
          android:background="#0000ff"
          android:layout_row="0"
          android:layout_column="0" /&gt;
      &lt;/GridLayout&gt;
  &lt;/RelativeLayout&gt;
  </code></pre>
  
  <p>But they are for v21 and above only. How to support <code>layout_columnWeight</code> and <code>layout_rowWeight</code> feature in pre API 21?</p>