In Android Studio, how do you configure gradle to automatically replace AdMob's AdUnitId when creating signed release APKs

Question

Standard guidance shows that this should be placed where the AdMob banner should be displayed in you MainActivity.xml:

<com.google.android.gms.ads.AdView
    android:id="@+id/adView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:gravity="bottom"
    android:background="@color/default_background"
    ads:adSize="SMART_BANNER"
    ads:adUnitId="@string/banner_ad_unit_id" />

In my strings.xml I have defined the following:

<string name = "banner_ad_unit_id" >
    ca-app-pub-3940256099942544/6300978111
    </string>

How do I get this value automatically replaced with my personal AdMob ID when creating a release build/signed apk file?

Answer 1

This is my solution for this problem, and I know it is not flawless, but it works quite well.

In app build.gradle you can define string resources upon buildTypes ('...' are other definitions not related):

build.gradle (app):

android{
   ...
   buildTypes{

      debug {  //Debug build type
         ...
         //In here only TestAd keys (theese are public test keys free to use)
         resValue("string","mobileads_app_id","ca-app-pub-3940256099942544~3347511713")
         resValue("string","banner_ad_unit_id_no_1","ca-app-pub-3940256099942544/6300978111")
         resValue("string","banner_ad_unit_id_no_2","ca-app-pub-3940256099942544/6300978111")
         resValue("string","interstitial_ad_unit_no_1","ca-app-pub-3940256099942544/1033173712")
         ...
      }

      release {  //Release build type
         ...
         //In here only your own production Ad keys
         resValue("string","mobileads_app_id","/*YOUR REAL MOBILEADS KEY*/")
         resValue("string","banner_ad_unit_id_no_1","/*YOUR REAL AD UNIT ID KEY*/")
         resValue("string","banner_ad_unit_id_no_2","/*YOUR REAL AD UNIT ID KEY*/")
         resValue("string","interstitial_ad_unit_no_1","/*YOUR REAL INTERSTITIAL AD KEY*/")
         ...
      }              
   } 
}

In your strings.xml you should comment that your Ad keys are defined in app build.gradle or you may loose track if you don't remember it...

strings.xml:

<resources>
...
    <!--Note !! AdView keys are defined in app.gradle for debug and release buildTypes -->
...
</resources>

You can now reference to the string definitions you have entered in the app build.gradle file as they were written in the strings.xml, and the correct value is selected upon debug release when debugging code, and release release when releasing code for the app store:

fragment_layout.xml:

    <com.google.android.gms.ads.AdView
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            ads:adSize="SMART_BANNER"
            ads:adUnitId="@string/banner_ad_unit_id_no_1"  
            android:id="@+id/fragment_no_1_adView"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="1.0"
            app:layout_constraintTop_toTopOf="parent" />

MainActivity.kt:

class MainActivity :AppCompatActivity(), FragmentOne.OnFragmentInteractionListener, ...
{
   ...
   override fun onCreate(savedInstanceState: Bundle?)
   {
      ...
      setContentView(R.layout.activity_main)

      //You can refer to the AdView code in string definition in a common way
      MobileAds.initialize(this,getString(R.string.mobileads_app_id))

      ... 

      interstitialAd = InterstitialAd(this)
      interstitialAd.adUnitId = getString(R.string.interstitial_ad_unit_no_1)

      ...

   }
}

fragment.kt:

class MyFragment : Fragment() {

override fun onCreateView(
    inflater: LayoutInflater,
    container: ViewGroup?,
    savedInstanceState: Bundle?): 
    View? {

    adRequest = AdRequest
        .Builder()
        .build()

    stationListAdView.loadAd(adRequest)

    (activity as MainActivity).stationListToPriceInterstitialAd.loadAd(AdRequest.Builder().build())

RG