title: button is not displaying in layout file android
body: <p>This is my layout file.    </p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      xmlns:tools="http://schemas.android.com/tools"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:fitsSystemWindows="true"
      tools:context=".ActivityMain"&gt;
  
      &lt;android.support.design.widget.AppBarLayout
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:id="@+id/toolbarLayer"
          android:theme="@style/AppTheme.AppBarOverlay"&gt;
  
          &lt;android.support.v7.widget.Toolbar
              android:id="@+id/toolbar"
              android:layout_width="match_parent"
              android:layout_height="?attr/actionBarSize"
              android:background="?attr/colorPrimary"
              app:popupTheme="@style/AppTheme.PopupOverlay" /&gt;
  
      &lt;/android.support.design.widget.AppBarLayout&gt;
  
      &lt;ListView
          android:id="@+id/users"
          android:layout_marginTop="40dp"
          android:padding="20dp"
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:layout_below="@+id/toolbarLayer"
          android:layout_above="@+id/button_add_new_user"
          /&gt;
  
      &lt;Button
          android:id="@+id/button_add_new_user"
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:text="Add New User"
          android:layout_alignParentBottom="true"
          /&gt;
  
  
  &lt;/android.support.design.widget.CoordinatorLayout&gt;
  </code></pre>
  
  <p>I want to display a button in bottom of the activity. but above code doesn't show a button.</p>
  
  <p>Can anyone help me what is wrong here? </p>