Windows Phone 8 - Getting Multiple Street Names - silverlight

Question

I created for Windows Phone 8.0 Silverlight App an async method GetStreetName
string streetname;
private async Task<string> GetStreetName(int i)
{
MapAddress address;
ReverseGeocodeQuery query = new ReverseGeocodeQuery();
query.GeoCoordinate = Route[i].Item1;
query.QueryCompleted += (s, e) =>
{
if (e.Error != null)
return;
address = e.Result[0].Information.Address;
streetname = address.Street;
};
query.QueryAsync();
return streetname;
}
and I call it using the await operator inside of a for loop:
for (int i = 0; i < Route.Count; i++)
{
ListBox.Items.Add(await GetStreetName(i));
}
but I always get only the street name of the first loaded geoposition back and I have no idea why (I thought the await operator is waiting until the async method is finished).
Additional info: i just saw that this is not 100% clear at this short snippet, streetname and Route are global "variables", Route is a tuple list where the first item is a geocoordinate.
How can I fix this issue?

Answer 1

You are returning from GetStreetName before the results are ready becayse query.QueryAsync(); just starts the query and doesn't wait for it to be complete.
On top of that, you're writing all results to the same global streetname.
You need to use a TaskCompletionSource.
Try something like this:
private async Task<string> GetStreetNameAsync(int i)
{
var tcs = new TaskCompletionSource<IEnumerable<string>>();
EventHandler<QueryCompletedEventArgs<IList<MapLocation>>> handler = (s, e) =>
{
if (e.Error != null)
{
tcs.TrySetException(e.Error);
return;
}
if (e.Cancelled)
{
tcs.TrySetCanceled();
return;
}
tcs.TrySetResult(e.Result[0].Information.Address.Street);
};
var query = new ReverseGeocodeQuery();
query.GeoCoordinate = Route[i].Item1;
try
{
query.QueryCompleted += handler;
query.QueryAsync();
return await tcs.Task;
}
finally
{
query.QueryCompleted -= handler;
}
}