java.lang.IllegalStateException: The ad unit ID can only be set once on InterstitialAd.

Describe the bug Sometimes when open app Google Play Console gives me the following info on the crashes:

java.lang.IllegalStateException: The ad unit ID can only be set once on InterstitialAd.
        at com.google.android.gms.internal.ads.zzxx.setAdUnitId(com.google.android.gms:play-services-ads-lite@@19.1.0:80)
        at com.google.android.gms.ads.InterstitialAd.setAdUnitId(com.google.android.gms:play-services-ads-lite@@19.1.0:17)
        at com.getcapacitor.community.admob.helpers.AdViewIdHelper.assignIdToAdView(AdViewIdHelper.java:37)
        at com.getcapacitor.community.admob.AdMob$2.run(AdMob.java:114)
        at android.os.Handler.handleCallback(Handler.java:873)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6669)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

Device: Google Pixel 2 API 28

Other info: my js code:

initializeApp() {
    this.platform.ready().then(() => {
        this.prepareConfig() ;
    });
}
optionsInterstitial: AdOptions;

prepareConfig() {
    if (Capacitor.platform !== 'web') {
        AdMob.initialize();
        this.prepareConfigInterstitial();
     }
}

prepareConfigInterstitial() {
    if (Capacitor.platform == 'ios') {
      this.optionsInterstitial = {
        adId: AppConfig.admob.interstitial.ios,
      }
    }
    if (Capacitor.platform == 'android') {
      this.optionsInterstitial = {
        adId: AppConfig.admob.interstitial.android,
      }
    }
    if (Capacitor.platform !== 'web') {
      AdMob.prepareInterstitial(this.optionsInterstitial)
        .then(
          async (value: any) => {
            console.log(value);  // true
          },
          (error: any) => {
            console.error(error); // show error
          }
        );
    }
  }

[distante]

AFAIK this happens when you call prepare two times (so the plugin tries to reassign the ad unit id). I suppose we could change the behavior in a way that is the banner was already loaded then nothing is done (and an error is returned) here: https://github.com/capacitor-community/admob/blob/9e153cd62f1736cf40c721ae2464b9005c04550c/android/src/main/java/com/getcapacitor/community/admob/AdMob.java#L105-L107

something like

if(mInterstitialAd == null) {
   // call some console error
    return
}

But you should take a look if you are calling prepare two times somewhere. Perhaps on a component constructor or similar.

[distante]

Hi, great work on this plugin, thanks! Just wondering how to show more than one Interstitial Ad? Not sure if i missed something? I thought i had to prepare each time?

Should mInterstitialAd be nulled again maybe on the show?

Yes you are half right, it should be nulled again, but on close:

https://github.com/capacitor-community/admob/blob/9e153cd62f1736cf40c721ae2464b9005c04550c/android/src/main/java/com/getcapacitor/community/admob/AdMob.java#L151-L155