Hide/Show Admob View Android plugin

I am showing admob in my unity app. I want to hide admob on another scene. Here is the code showing how I am making admob view and importing it to unity as plugin. AdMob is showing perfectly fine. Now my concern is how to hide and show it again using some function calls.

 public class AdMob
 {
     private String pubID = "xxxx"; //Your public AdMob ID. Make sure this is correct, or you wont get any credit for the Ad.
     private Activity activity; //Store the android main activity
     private AdView adView; //The AdView we will display to the user
     private RelativeLayout layout; //The layout the AdView will sit on
     //Constructor
     AdMob()
     {
         activity = UnityPlayer.currentActivity;
         activity.runOnUiThread(new Runnable() {
             
             @Override
             public void run() {
                 // TODO Auto-generated method stub
                 layout = new RelativeLayout(activity);
                 
                 activity.addContentView(layout,new LayoutParams(LayoutParams.WRAP_CONTENT,LayoutParams.WRAP_CONTENT));
                 adView = new AdView(activity,AdSize.SMART_BANNER,pubID);
                 adView.loadAd(new AdRequest());
                 AdView.LayoutParams adViewParams = new AdView.LayoutParams(AdView.LayoutParams.WRAP_CONTENT,
                         AdView.LayoutParams.WRAP_CONTENT);
                     //the next line is the key to putting it on the bottom
                     adViewParams.addRule(AdView.ALIGN_PARENT_BOTTOM);
                 layout.addView(adView.getRootView(),adViewParams);
             }
         });
     }

Now I want to write a function something like this which I will call while switching my scenes. Same thing goes with showing admob.

  public void hideAdmob(){
 
         adView.setVisibility(View.GONE);
 
     }

but this thing or other tries just crashes my app when I switch scene.

Any help guys. Thanks a lot.