I haven't had success either in getting a consistent geocode result using just a country code ("USA" seems to work, others do not).
There's an example on the developers.arcgis.com site that does this successfully (https://developers.arcgis.com/en/features/geocoding/), but uses a combination of "suggest" (to get the desired country) and "find" (to retrieve the result).
One option is to simply query a country boundary service for the geometry and find the center (of the extent, e.g.). For example:
var queryUrl = "http://services.arcgis.com/P3ePLMYs2RVChkJx/arcgis/rest/services/World_Countries_(Generalized)/Featu...";
var queryTask = new QueryTask(new Uri(queryUrl));
var queryExp = "ISO = '" + this.CountryTextBox.Text + "'"; // SG, US, DK, for example (two-letter codes)
// var queryExp = "Country ='" + this.CountryTextBox.Text + "'"; // Singapore, United States, Denmark, for example
var countryQuery = new Query(queryExp);
var result = await queryTask.ExecuteAsync(countryQuery);
if (result.FeatureSet.Features.Count > 0)
{
var countryExtent = result.FeatureSet.Features[0].Geometry.Extent as Envelope;
var countryCenter = countryExtent.GetCenter();
await this.MyMapView.SetViewAsync(countryCenter);
MessageBox.Show("Center of '" +
this.CountryTextBox.Text + "' is " +
countryCenter.X.ToString() + " : " +
countryCenter.Y.ToString());
}
else
{
MessageBox.Show("No results found for '" + this.CountryTextBox.Text + "'.");
}
