title: Add load animation to custom dialog in kotlin
body: <p>I want to add load animation to custom dialog, I was able to do it in java but I m having issue to do the same in kotlin it gives me the below error</p>
  
  <pre><code>E/AndroidRuntime: FATAL EXCEPTION: main
  android.util.AndroidRuntimeException: requestFeature() must be called before adding content
  at com.android.internal.policy.impl.PhoneWindow.requestFeature(PhoneWindow.java:229)
  at com.android.internal.app.AlertController.installContent(AlertController.java:234)
  at android.app.AlertDialog.onCreate(AlertDialog.java:337)
  at android.app.Dialog.dispatchOnCreate(Dialog.java:355)
  at android.app.Dialog.show(Dialog.java:260)
  at com.autodroid.demo.MainActivity.show(MainActivity.kt:66)
  at com.autodroid.demo.MainActivity$onCreate$1.onClick(MainActivity.kt:32)
  at android.view.View.performClick(View.java:4204)
  at android.view.View$PerformClick.run(View.java:17355)
  at android.os.Handler.handleCallback(Handler.java:725)
  at android.os.Handler.dispatchMessage(Handler.java:92)
  </code></pre>
  
  <p>Below is my code to create a dialog in kotlin</p>
  
  <pre><code> val dialogBuilder = AlertDialog.Builder(activity)
          val inflater = activity?.layoutInflater
          val dialogView = inflater?.inflate(R.layout.newly_dialog, null)
          dialogBuilder.setView(dialogView)
  
          val tvPopText = dialogView?.findViewById&lt;View&gt;(R.id.tvPopText) as TextView
  
          val dBuilder = dialogBuilder.create()
  
          //-----&gt; Issue  :( 
          var viewGroup = dBuilder.window.decorView
          viewGroup.startAnimation(AnimationUtils.loadAnimation(activity, R.anim.slide_down))
        //-----&gt; Issue
  
          dBuilder.show()
  </code></pre>
  
  <p>Any pointer will be appreciated , Thanks in advance :)</p>