Question

Is the Callback supposed to be called on a different thread?
Using this code:

client.ExecuteAsync<List<IngredientDto>>(request, Response =>
    {
        textBox1.Text += Response.Data.Count;
    });

I get a “InvalidOperationException”:

“The calling thread cannot access this object because a different thread owns it.”

Shouldn’t the callback be on the UI thread, or am I wrong?

Answer 1

Actually, if you look at source code, you’ll see

    public virtual RestRequestAsyncHandle ExecuteAsync<T>(IRestRequest request, Action<IRestResponse<T>, RestRequestAsyncHandle> callback)
    {
        return ExecuteAsync(request, (response, asyncHandle) =>
        {
            IRestResponse<T> restResponse = response as RestResponse<T>;
            if (response.ResponseStatus != ResponseStatus.Aborted)
            {
                restResponse = Deserialize<T>(request, response);
            }

            callback(restResponse, asyncHandle);//<--- this means that response & callback are executed at **same** thread.
        });
    }

That leads to:
You can’t update ui objects from non-ui thread. In case of WPF you can use Dispatcher

client.ExecuteAsync<List<IngredientDto>>(request, Response =>
    {
        Dispatcher.Invoke((Action)() => {textBox1.Text += Response.Data.Count;});
    });

In general case see syncronization context