Asynchronously performs a forward geocoding query using a web service.
Use search to do the same thing synchronously.
When the operation is finished, callback will be called. You can then call search_async.end to
get the result of the operation.
| this |
a Forward representing a query |
| cancellable |
optional Cancellable forward, null to ignore. |
| callback |
a TaskReadyCallback to call when the request is satisfied |
| user_data |
the data to pass to callback function |