/// <summary>
/// Updates the weather forecast.
/// </summary>
/// <param name="state">The state (required for TimerCallback)</param>
private void UpdateWeatherForecast(Object state)
{
// timer callbacks can queue up and fire all at once. Of course in this case,
// the interval is 4 hours, so we won’t see any callbacks queue up, but if the
// interval was a few seconds, it would be possible.
if (Interlocked.Exchange(ref _inTimerCallback, 1) != 0) {
return;
}
try
{
// if someone disposed us, do nothing
if (_disposed == 1)
{
return;
}
// attempt to retrieve the weather forecast data
WeatherForecastData updatedForecast = GetForecastForUpcomingMarket();
if (updatedForecast != null)
{
_forecastDataLock.AcquireWriterLock(Timeout.Infinite);
_forecastData = updatedForecast;
_forecastDataLock.ReleaseWriterLock();
}
// if we succeed, update in 4 hours, otherwise retry in 2 minutes
TimeSpan newTimeSpan = ((updatedForecast != null) && updatedForecast.IsValid()) ?
new TimeSpan(4, 0, 0) : new TimeSpan(0, 2, 0);
_timer.Change(newTimeSpan, newTimeSpan);
}
finally
{
Interlocked.Exchange(ref _inTimerCallback, 0);
}
}
/// <summary>
/// Gets the forecast for upcoming market day.
/// </summary>
/// <returns></returns>
private static WeatherForecastData GetForecastForUpcomingMarket()
{
WeatherForecastData result;
// determine the local date/time for the start of this Saturday's market
int daysTilSaturday = DayOfWeek.Saturday - DateTime.Today.DayOfWeek;
DateTime marketStarts = DateTime.Today.AddDays(daysTilSaturday).AddHours(8);
// geographic location of Carpterter Village
const decimal latitude = (decimal)35.8188612;
const decimal longitude = (decimal)-78.8594969;
// create an instance of the web service proxy
var weatherFetcher = new ndfdXML {Proxy = WebRequest.DefaultWebProxy};
// setup the parameters to tell the service what data we want
// see http://www.nws.noaa.gov/forecasts/xml/docs/elementInputNames.php for parameters
var weatherParams = new weatherParametersType
{
appt = true,
icons = true,
maxt = true,
mint = true,
pop12 = true,
rh = true,
wx = true,
wwa = true,
wspd = true
};
try
{
result = WeatherForecastData.Parse(weatherFetcher.NDFDgen(latitude, longitude, "time-series",
marketStarts.ToUniversalTime(), marketStarts.AddHours(4).ToUniversalTime(), weatherParams));
}
catch (Exception)
{
result = new WeatherForecastData();
}
return result;
}
/// <summary>
/// Initializes a new instance of the <see cref="WeatherForecastTimer"/> class.
/// </summary>
public WeatherForecastTimer()
{
// assume failure
bool dispose = true;
try
{
// register event handler on unload of the app domain to dispose the timer
AppDomain appDomain = Thread.GetDomain();
var onAppDomainUnload = new EventHandler(OnAppDomainUnload);
appDomain.DomainUnload += onAppDomainUnload;
_onAppDomainUnload = onAppDomainUnload;
WeatherForecastData forecastData = GetForecastForUpcomingMarket();
if (forecastData != null)
{
_forecastDataLock.AcquireWriterLock(Timeout.Infinite);
_forecastData = forecastData;
_forecastDataLock.ReleaseWriterLock();
}
// if we get the forecast successfully, start the timer in 4 hours, otherwise
// try again in 2 minutes
var dueTime = ((forecastData != null) && forecastData.IsValid()) ?
new TimeSpan(4, 0, 0) : new TimeSpan(0, 2, 0);
// create the timer
_timer = new Timer(UpdateWeatherForecast, null, dueTime, new TimeSpan(4, 0, 0));
// if we've gotten this far, we don't need to dispose ourselves
dispose = false;
}
finally
{
if (dispose)
{
Dispose();
}
}
}
public WeatherForecastData GetForecastData()
{
WeatherForecastData data;
try
{
_forecastDataLock.AcquireReaderLock(100);
data = (WeatherForecastData)_forecastData.Clone();
_forecastDataLock.ReleaseReaderLock();
}
catch (ApplicationException)
{
data = new WeatherForecastData();
}
return data;
}
/// <summary>
/// Parses the specified XML response from the National Weather Service (NWS)
/// to the appropriate data fields.
/// </summary>
/// <param name="xml">The XML response from the NWS.</param>
/// <returns></returns>
public static WeatherForecastData Parse(string xml)
{
var data = new WeatherForecastData();
try
{
var doc = new XmlDocument();
doc.LoadXml(xml);
data.Source = doc.SelectSingleNode("//title/text()").InnerText;
data.ForecastDateTime = DateTime.Parse(doc.SelectSingleNode(
"/dwml/data/time-layout[1]/start-valid-time[1]/text()").InnerText);
XmlNodeList tempNodes = doc.SelectNodes("/dwml/data/parameters/temperature[@type=\"apparent\"]/value");
data.TemperatureHigh = Convert.ToInt32(doc.SelectSingleNode(
"/dwml/data/parameters/temperature[@type=\"apparent\"]/value[1]/text()").InnerText);
if ((tempNodes != null) && (tempNodes.Count > 1))
{
data.TemperatureLow = Convert.ToInt32(doc.SelectSingleNode(
"/dwml/data/parameters/temperature[@type=\"apparent\"]/value[2]/text()").InnerText);
// swap the high and low values if necessary
if (data.TemperatureLow > data.TemperatureHigh)
{
data.TemperatureLow ^= data.TemperatureHigh;
data.TemperatureHigh ^= data.TemperatureLow;
data.TemperatureLow ^= data.TemperatureHigh;
}
}
data.IconUri = doc.SelectSingleNode("//icon-link").InnerText;
data.MoreInformationUri = doc.SelectSingleNode("//moreWeatherInformation/text()").InnerText;
data.ProbabilityOfPrecipitation = Convert.ToInt32(doc.SelectSingleNode(
"/dwml/data/parameters/probability-of-precipitation/value/text()").InnerText);
data.WindSpeedHigh = Convert.ToInt32(doc.SelectSingleNode(
"/dwml/data/parameters/wind-speed/value[1]/text()").InnerText);
tempNodes = doc.SelectNodes("/dwml/data/parameters/wind-speed/value");
if ((tempNodes != null) && (tempNodes.Count > 1))
{
data.WindSpeedLow = Convert.ToInt32(doc.SelectSingleNode(
"/dwml/data/parameters/wind-speed/value[2]/text()").InnerText);
}
}
catch (NullReferenceException exNull)
{
Debug.WriteLine(exNull.Message);
data.Source = String.Empty;
}
catch (InvalidOperationException exOp)
{
Debug.WriteLine(exOp.Message);
data.Source = String.Empty;
}
catch (XPathException exXPath)
{
Debug.WriteLine(exXPath.Message);
data.Source = String.Empty;
}
return data;
}
