Question

I made a WPF example that consumes a web service (http://www.webservicex.com/globalweather.asmx) in two different ways:

with events like this:

public Window1()
{
    InitializeComponent();
    DataContext = this;

    Location = "loading...";
    Temperature = "loading...";
    RelativeHumidity = "loading...";

    client.GetWeatherCompleted += 
            new EventHandler<GetWeatherCompletedEventArgs>(client_GetWeatherCompleted);
    client.GetWeatherAsync("Berlin", "Germany");
}

void client_GetWeatherCompleted(object sender, GetWeatherCompletedEventArgs e)
{
    XDocument xdoc = XDocument.Parse(e.Result);

    Location = xdoc.Descendants("Location").Single().Value;
    Temperature = xdoc.Descendants("Temperature").Single().Value;
    RelativeHumidity = xdoc.Descendants("RelativeHumidity").Single().Value;
}

and with the Begin/End methods and IAsyncResult like this:

public Window1()
{
    InitializeComponent();
    DataContext = this;

    Location = "loading...";
    Temperature = "loading...";
    RelativeHumidity = "loading...";

    client.BeginGetWeather("Berlin", "Germany", new AsyncCallback(GotWeather), null);
}

void GotWeather(IAsyncResult result)
{
    string xml = client.EndGetWeather(result).ToString();
    XDocument xdoc = XDocument.Parse(xml);

    Location = xdoc.Descendants("Location").Single().Value;
    Temperature = xdoc.Descendants("Temperature").Single().Value;
    RelativeHumidity = xdoc.Descendants("RelativeHumidity").Single().Value;

}

These two approaches seem to perform the exact same task.

What are their advantages and disadvantages? When would you use one and not the other?

Answer 1

For the case of remote services, I usually prefer to use callbacks instead of event handlers since it leads to more readable/maintainable code (by just looking at the service call invokation code I know which code will be executed when the call finishes). Moreover when using event handlers you need to have care for not declaring them more than once.