Having problems with XML

Question

This code, located below, is designed to pull an XML file from the internet and parse it below. However, an exception (NullReferanceExeption) is caused when I attempt to extract a value from this XML file.

Here's the code, the line has been noted where the error is occurring:

Below the code is the XML file I am trying to extract the value from.

//Create the forecast
void makeforecast()
{
    //Make Webclient Request
    WebClient client = new WebClient();
    client.DownloadStringAsync(new Uri("http://api.wt360.com/data/forecast/daily-4day?key=ic1uji3s9zjnjgcd6hq64ny6alkoin9119vjrxc1wwngdzuihk&l=" + latitude + "," + longitude + "&fmt=xml"));
    client.DownloadStringCompleted += (s, n) =>
    {
        progress.Visibility = System.Windows.Visibility.Collapsed;
        ((Storyboard)this.Resources["trans"]).Begin();
        XDocument xDoc = XDocument.Parse(n.Result);

        //Current Conditions
        if (debug2.Text == "Temp")
        {
        }
        if (debug2.Text == "Sun")
        {
        }
        if (debug2.Text == "Rain")
        {
           THIS LINE CAUSES THE EXEPTION >> tempnow.Text = xDoc.Root.Element("forecast").Element("pop").Value;**
        }
    }
}

And the XML:

<data>
<status>success</status>
<location>
<city/>
<fullName>39.6N, 0.3W - 6miles SW of El Puerto, SP</fullName>
<localDate>2014-01-30T01:29:23</localDate>
<localEpoch>1391045363</localEpoch>
<locationID>GP202368</locationID>
</location>
<forecast>
<record>0</record>
<utcEpoch>1391040000</utcEpoch>
<utcDate>2014-01-30T00:00:00</utcDate>
<maxTempC>15.4</maxTempC>
<maxTempF>59.7</maxTempF>
<minTempC>5.2</minTempC>
<minTempF>41.3</minTempF>
<fcstDay>1</fcstDay>
<dayLength>10:07</dayLength>
<sunriseHHMMLocal>8:11am</sunriseHHMMLocal>
<sunsetHHMMLocal>6:18pm</sunsetHHMMLocal>
<nightLength/>
<moonriseHHMMLocal/>
<moonsetHHMMLocal/>
<moonphase/>
<moonillum/>
<moonicon/>
<pop>19</pop>
<uv_index>2</uv_index>
<gustC>30</gustC>
<gustF>19</gustF>
<heatindexC>-999.99</heatindexC>
<heatindexF>-999.99</heatindexF>
<icon>partly-cloudy-sm.png</icon>
<iconBase>partly-cloudy</iconBase>
<iconLg>partly-cloudy.png</iconLg>
<prcpC>0</prcpC>
<prcpF>0</prcpF>
<rh>33</rh>
<skyCover>8</skyCover>
<snowC>0</snowC>
<snowF>0</snowF>
<wdir>NW</wdir>
<windchillC>-999.99</windchillC>
<windchillF>-999.99</windchillF>
<wspdC>16</wspdC>
<wspdF>10</wspdF>
<wx>Mostly Sunny</wx>
</forecast>
<forecast>
<record>1</record>
<utcEpoch>1391126400</utcEpoch>
<utcDate>2014-01-31T00:00:00</utcDate>
<maxTempC>16</maxTempC>
<maxTempF>60.8</maxTempF>
<minTempC>5</minTempC>
<minTempF>40.9</minTempF>
<fcstDay>2</fcstDay>
<dayLength>10:09</dayLength>
<sunriseHHMMLocal>8:10am</sunriseHHMMLocal>
<sunsetHHMMLocal>6:19pm</sunsetHHMMLocal>
<nightLength/>
<moonriseHHMMLocal/>
<moonsetHHMMLocal/>
<moonphase/>
<moonillum/>
<moonicon/>
<pop>18</pop>
<uv_index>2</uv_index>
<gustC>30</gustC>
<gustF>19</gustF>
<heatindexC>-999.99</heatindexC>
<heatindexF>-999.99</heatindexF>
<icon>partly-cloudy-sm.png</icon>
<iconBase>partly-cloudy</iconBase>
<iconLg>partly-cloudy.png</iconLg>
<prcpC>0</prcpC>
<prcpF>0</prcpF>
<rh>46</rh>
<skyCover>28</skyCover>
<snowC>0</snowC>
<snowF>0</snowF>
<wdir>WNW</wdir>
<windchillC>-999.99</windchillC>
<windchillF>-999.99</windchillF>
<wspdC>13</wspdC>
<wspdF>8</wspdF>
<wx>Mostly Sunny</wx>
</forecast>
<forecast>
<record>2</record>
<utcEpoch>1391212800</utcEpoch>
<utcDate>2014-02-01T00:00:00</utcDate>
<maxTempC>18.1</maxTempC>
<maxTempF>64.5</maxTempF>
<minTempC>6.4</minTempC>
<minTempF>43.5</minTempF>
<fcstDay>3</fcstDay>
<dayLength>10:12</dayLength>
<sunriseHHMMLocal>8:09am</sunriseHHMMLocal>
<sunsetHHMMLocal>6:21pm</sunsetHHMMLocal>
<nightLength/>
<moonriseHHMMLocal/>
<moonsetHHMMLocal/>
<moonphase/>
<moonillum/>
<moonicon/>
<pop>46</pop>
<uv_index>2</uv_index>
<gustC>49</gustC>
<gustF>31</gustF>
<heatindexC>-999.99</heatindexC>
<heatindexF>-999.99</heatindexF>
<icon>light-rain-shower-sm.png</icon>
<iconBase>light-rain-shower</iconBase>
<iconLg>light-rain-shower.png</iconLg>
<prcpC>0.2</prcpC>
<prcpF>0.09</prcpF>
<rh>35</rh>
<skyCover>27</skyCover>
<snowC>0</snowC>
<snowF>0</snowF>
<wdir>WNW</wdir>
<windchillC>-999.99</windchillC>
<windchillF>-999.99</windchillF>
<wspdC>22</wspdC>
<wspdF>14</wspdF>
<wx>Light Rain Showers</wx>
</forecast>
<forecast>
<record>3</record>
<utcEpoch>1391299200</utcEpoch>
<utcDate>2014-02-02T00:00:00</utcDate>
<maxTempC>15.9</maxTempC>
<maxTempF>60.7</maxTempF>
<minTempC>4.2</minTempC>
<minTempF>39.6</minTempF>
<fcstDay>4</fcstDay>
<dayLength>10:14</dayLength>
<sunriseHHMMLocal>8:08am</sunriseHHMMLocal>
<sunsetHHMMLocal>6:22pm</sunsetHHMMLocal>
<nightLength/>
<moonriseHHMMLocal/>
<moonsetHHMMLocal/>
<moonphase/>
<moonillum/>
<moonicon/>
<pop>12</pop>
<uv_index>2</uv_index>
<gustC>41</gustC>
<gustF>26</gustF>
<heatindexC>-999.99</heatindexC>
<heatindexF>-999.99</heatindexF>
<icon>sunny-sm.png</icon>
<iconBase>sunny</iconBase>
<iconLg>sunny.png</iconLg>
<prcpC>0</prcpC>
<prcpF>0</prcpF>
<rh>34</rh>
<skyCover>0</skyCover>
<snowC>0</snowC>
<snowF>0</snowF>
<wdir>WNW</wdir>
<windchillC>-999.99</windchillC>
<windchillF>-999.99</windchillF>
<wspdC>19</wspdC>
<wspdF>12</wspdF>
<wx>Sunny</wx>
</forecast>
</data>

Please do not link this as a duplicate of NullReferenceException with XML Document as major changes have been made to the code.

Answer 1

You don't seem to be checking that the XML is as you expect here. For instance when I run your code I get the following XML back:

<?xml version="1.0" encoding="utf-8"?>
<data>
   <status>error</status>
   <errorCode>00001</errorCode>
   <errorMessage>Request quota has been exceeded.  Please contact support.</errorMessage><errorMethod></errorMethod>
   <errorModule>api</errorModule>
</data>

You need to check the status element first.

if(xDoc.Root.Element("status").ToString().ToLower() == "success") 
    //run your code

Answer 2

No one else can debug your code properly, because you are calling a url which we cannot determine (you have the unknown variables latitude and longitude.

I've debugged the line xDoc.Root.Element("forecast").Element("pop").Value, where xDoc is created from the long xml text you gave, and there's no exception. So I can suggest the following.

1. Make sure n.Result is what you think it is. Log it somewhere to make sure it's not a blank string, or a json string, or anything else unexpected.

2. Try to find out exactly where the null reference exception is occurring. To do this, unchain all those method calls, and have one method call per line:

   var root = xDoc.Root;
   var forecast = root.Element("forecast");
   var pop = forecast.Element("pop");
   var popValue = pop.Value;
   tempnow.Text = popValue;
   

Then at least you'll know exactly where you exception is coming from.