IAds Banner help. If IAds isn't showing show admob.

I’m using this code but I don’t know how to check if the ad is showing. If the ad isn’t showing i wan’t it to show an admob ad and if the IAds start to show, remove the admob and show the IAds.

using UnityEngine;
using System.Collections;

public class IAdScript : MonoBehaviour {

	private ADBannerView banner = null;
	void Start()
	{
		banner = new ADBannerView(ADBannerView.Type.Banner, ADBannerView.Layout.Bottom);
		ADBannerView.onBannerWasClicked += OnBannerClicked;
		ADBannerView.onBannerWasLoaded  += OnBannerLoaded;
	}
	void OnBannerClicked()
	{
		Debug.Log("Clicked!

");
}
void OnBannerLoaded()
{
Debug.Log("Loaded!
");
banner.visible = true;
}
}

Contact me for demo of iAd and AdMob
Email : sudhir.kotila@gmail.com