Why does AdMob return NO FILL

I'm using an AdMob view in an android app, but I'm unable to get any ad into the app.

For reference, I've added the view to a ListView as explained by Dan Dyer here

EDIT: I'm using GoogleAdMobAdsSdk-4.1.1. The release notes of Google AdMob Ads SDK for version 4.1.0 says:

"... - Added support for AdRequest.addTestDevice() and AdRequest.setTestDevices(). Note that AdRequest.setTesting() is now deprecated. ..."

This is how the ad is inserted to my ListView:

public View getView(int position, View convertView, ViewGroup parent) {

  // Some other code
  // Reusing convertView etc.

  AdView adView = 
     new AdView((Activity) getContext(), AdSize.BANNER, 
     "/xxxxxx/ca-pub-xxxxxxx/my_ad_unit");
  for (int i = 0; i < adView.getChildCount(); i++) {
    adView.getChildAt(i).setFocusable(false);
  }
  adView.setFocusable(false);
  float density = getContext().getResources().getDisplayMetrics().density;
  int height = Math.round(50 * density);
  AbsListView.LayoutParams params = new AbsListView.LayoutParams(
    AbsListView.LayoutParams.FILL_PARENT, height);

  adView.setLayoutParams(params);
  AdRequest request = new AdRequest();
  request.addTestDevice("xxxxxxxxxxxxxxxxx");
  adView.loadAd(request);

  // other stuff
  // returning convertView
}

I've also added an AdListener to the adview, and on every loadAd, the onFailedToReceiveAd callback method is called:

public void onFailedToReceiveAd(Ad arg0, ErrorCode arg1) {
  Log.d(TAG, "AdMob in list failed to receive ad: " + arg1.name());
}

In logcat I get this message:

08-17 15:22:18.065: AdMob in list failed to receive ad: NO_FILL

Can anyone tell me what this errorcode means?

Solution

To answer the question:

NO_FILL is returned from AdMob when there is no inventory left to serve in the AdMob/DFP backend.

First of all this meant I was requesting an ad of size AxB, but the backend had no ads of this size left to show. It is important that the size you request has inventory left in the backend systems of AdMob/DFP.

Second, their API states that the first time you request an ad to a specific ad unit, you should expect up to two minutes before the ads start serving. I don't know if it is because I am not stationed in the US, but these two minutes often becomes at least 20 minutes if not several hours for me.