How to check if array exists?

Question

I am parsing HTML to an array using the following code.

void client_DownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e)
  {
 var html = e.Result;
 var doc = new HtmlDocument();
 doc.LoadHtml(html); 

 var list = doc.DocumentNode.Descendants("div").ToList();
 var node = doc.DocumentNode.Descendants("table")   
           .FirstOrDefault(x => x.Id == "departures")   
           .Element("tbody")          .Elements("tr") 
           .Select(tr => tr.Elements("td")
           .Select(td => td.InnerText).ToArray()).ToArray();

I am then outputing to Texblock with the below code.

//first line 
textBlock1.Text = node[0][0];
textBlock2.Text = node[0][1];
textBlock3.Text = node[0][2];

  //Second line
 textBlock4.Text = node[1][0];
 textBlock5.Text = node[1][1];
 textBlock6.Text = node[1][2];

  //Third line 
textBlock7.Text = node[2][0];
textBlock8.Text = node[2][1];
textBlock9.Text = node[2][2];

My issue is this: The HTMl changes through the day, so some times there isn't and [2] and sometimes there is up to [12].

What I would like to know is how can I wite a conditional statment to check if the array exists and only output if it has a value.

I have tried a conditional statement like below, but it still shows a Unhandled exception when there aren't any node[2] or node[1] results

if (node[2][0].length > 0)
   {
       textBlock1.Text = node[2][0];
    }

Any help will be apprecaited. If you need clarification on this please let me know.

@Egor I have tried that but it doesn't work. I guess because in some cases the node[2], node[3etc... elements dont exist. Its a strange one. I also thought that the node length condition would work. — Rhys
– Rhys, Commented Sep 16, 2011 at 0:18
One core problem seems to be that the text boxes are not variadic but are fixed (box1, box2, etc). Consider using a different control instead, perhaps a list control of sorts. Then n items can be added uniformly (and just using a loop construct). Text boxes can also be dynamically created, but this would not be my first choice. — user166390
– user166390, Commented Sep 16, 2011 at 0:24
As for the checking, all dimensions must be ensured, e.g. if (node.length > 2 && node[2].length > 0) { /* okay to use node[2][0] */ } — user166390
– user166390, Commented Sep 16, 2011 at 0:27
@pst Thanks for the information, I agree the textblock probably isn't the best setup, but I was limited by my ability. I will try your error checking tonight — Rhys
– Rhys, Commented Sep 16, 2011 at 0:30

user166390 · Accepted Answer · 2011-09-16 02:35:52Z

1

To avoid the invalid index, all the dimensions must be ensured, e.g.

if (node.length > 2 && node[2].length > 0) {
    // Okay to use node[2][0]
    // Since && is short-circuiting it will never make second
    // check if first fails.
}

To me, a more fundamental issue seems to be that the text boxes are not variadic but are fixed (box1, box2, etc). Consider using a different control instead, perhaps a list control of sorts. Then n items can be added uniformly (and just using a loop construct without need for the first index check). Text boxes can also be dynamically created, but this would not be my first choice.

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