Required XML attribute "adSize" was missing

I have same problem.

Solution for me:

 xmlns:ads=""

changed to

xmlns:ads="http://schemas.android.com/apk/res-auto"

Here is a weird answer. I just restarted my eclipse and it stared working. This might help some one.

Just restart eclipse, android studio or IntelliJ IDE

Try changing your declaration this way:

<com.google.android.gms.ads.AdView
    xmlns:ads="http://schemas.android.com/apk/res-auto"
    android:id="@+id/adView"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    ads:adUnitId="YOUR_AD_UNIT_ID"
    ads:adSize="BANNER"/>

---- EDIT ----

You can also try to do it programmatically. Simply, instead of an AdView layout item, define a LinearLayout and by code do something like this:

final AdView adView = new AdView(getActivity());
adView.setAdUnitId("YourId");
adView.setAdSize(AdSize.BANNER);

final LinearLayout adLinLay = (LinearLayout) view.findViewById(R.id.your_defined_linearlayout);
adLinLay.addView(adView);

final AdRequest.Builder adReq = new AdRequest.Builder();
final AdRequest adRequest = adReq.build();
adView.loadAd(adRequest);