I have wrote a c# function in order to parse an XML Stream.
My XML can have several nodes.
Example :
<Stream>
<One>nnn</One>
<Two>iii</Two>
<Three>jjj</Three>
</Stream>
But sometimes, it is :
<Stream>
<Two>iii</Two>
</Stream>
Here is my c# code :
var XML = from item in XElement.Parse(strXMLStream).Descendants("Stream") select item;
string strOne = string.Empty;
string strTwo = string.Empty;
string strThree = string.Empty;
if ((item.Element("One").Value != "")
{
strOne = item.Element("One").Value;
}
if ((item.Element("Two").Value != "")
{
strTwo = item.Element("Two").Value;
}
if ((item.Element("Three").Value != "")
{
strThree = item.Element("Three").Value;
}
With this code, if my Stream is full ( Node On, Two and three), there's no problem! But, if my Stream has only the node "Two", I get a NullReferenceException.
Is there a way to avoid this exception (I cannot change my Stream).
Thanks a lot :)
You should check if item.Element("anything") is null before accessing it's Value property.
if (item.Element("Three") != null && item.Element("Three").Value != "")
You need to do:
if (item.Element("One") != null)
{
strOne = item.Element("One").Value;
}
.Element(String) returns null if an element of the name you requested does not exist.
Checking if value != "" is pointless, because all you are preventing is the reassignment of an empty string to the strOne variable, which is already an empty string. Also, if you really needed to do the empty string check, using String.IsNullOrEmpty(String) method is the preferred way.
Instead of accessing Value property (which raises NullReferenceException if element not exist, as you already know) cast elements to strings. You can use ?? to provide default value for non-existing elements:
string strOne = (string)item.Element("One") ?? String.Empty;
string strTwo = (string)item.Element("Two") ?? String.Empty;
string strThree = (string)item.Element("Three") ?? String.Empty;
Related
I have a foreach loop that is pulling data from an XML file, however some fields are blank. When the loop tries to pull a specific value it will sometimes get a null reference exception. Is there a way to single out the variable that has the null value and set it to an empty string while displaying all the other values in an efficient way? For the sake of the example lets say the address field is returning the null value.
XmlDocument xmldoc = new XmlDocument();
xmldoc.Load(id);
XmlNodeList person = xmldoc.SelectNodes("//parent/child");
foreach (XmlNode node in person)
{
try
{
var name = node["name"].InnerText;
var phone = node["phone"].InnerText;
var email = node["email"].InnerText;
var address = node["address"].InnerText;
lblPopulate2.Text = name;
lblPopulate7.Text = address;
lblPopulate5.Text = phone;
lblPopulate6.Text = email;
}
catch(NullReferenceException ex)
{
???
}
finally
{
}
You could use the null conditional operator which would return null if the address node is not present, otherwise the InnerText.
var address = node["address"]?.InnerText;
And then the null coalescing operator for setting your Text property:
lblPopulate7.Text = address ?? string.Empty;
I am custom importing some rows from a text file to our database and so I have bunch of codes like this for many fields.
address.State = row["Location State"].ToString();
I just noticed a requirement that says
don't overwrite those fields in the value that we are reading from the
text file is empty or blank.
So I assume I can wrap them all around a check like this?
if(!String.IsNullOrEmpth(row["Location State"].ToString()))
address.State = row["Location State"].ToString();
But before I go ahead and apply this kind of logic around all those fields I wanted to check and see if you have better solutions?
Maybe an extension method could help here:
public static string ColumnValueOrDefault(this DataRow row, string column, string defaultValue)
{
if (row == null)
{
throw new ArgumentNullException("row");
}
if (column == null)
{
throw new ArgumentNullException("column");
}
if (defaultValue == null)
{
throw new ArgumentNullException("defaultValue");
}
var rowString = row[column].ToString();
return string.IsNullOrEmpty(rowString) ? defaultValue : rowString;
}
Address.State = row.ColumnValueOrDefault("column", Address.State);
I would (and do) use this pattern personally :
string sTester = string.Empty
Address.State = string.IsNullOrEmpty(sTester = row["collumn"].ToString()) == false ? sTester : Address.State;
This allows each collumn value to be set once, and the reused using the same string variable, and is relatively readable
I'm getting a text string from a website and parsing it into an XDocument. I'm looking to feed the value of certain elements into a very simple object (named NWSevent). My problem is that the original string changes and the XML tree varies; sometimes there are numerous events, up to 40, sometimes there is only one, and sometimes there is only one that does not have all the characteristics. If there are no alerts, then the "event" element has a title, but no areaDesc, summary, or severity.
I have two constructors for NWSevent, one takes in a single string, the other takes in four string arguments. I'm having trouble getting around a NullReferenceException. The if statement below can't do it because there is no value to compare. I'd appreciate any help.
public static void ParseWeatherData(String xmlString)
{
String ticker = string.Empty;
XDocument root = XDocument.Parse(xmlString);
XNamespace ns = XNamespace.Get("http://www.w3.org/2005/Atom");
XNamespace nsCap = XNamespace.Get("urn:oasis:names:tc:emergency:cap:1.1");
//get list of entry elements, set conditions for title, areaDesc, etc
var xlist = root.Descendants(ns + "entry").Select(elem => new
{ //use first or default to deal with possiblity of null return
Title = elem.Descendants(ns + "title").FirstOrDefault(),
AreaDesc = elem.Descendants(nsCap + "areaDesc").FirstOrDefault(),
Severity = elem.Descendants(nsCap + "severity").FirstOrDefault(),
Summary = elem.Descendants(ns + "summary").FirstOrDefault()
});
foreach (var el in xlist) //need to address null values when no alerts
{
if (el.AreaDesc.Value != null) //causes yellow null ERROR; no value exists for el.areaDesc.value
{
String titleIn = el.Title.Value;
String areaIn = el.AreaDesc.Value;
String severityIn = el.Severity.Value;
String summaryIn = el.Summary.Value;
new Models.NWSevent(titleIn, areaIn, severityIn, summaryIn);
}
else
{
String titleIn = el.Title.Value;
new Models.NWSevent(titleIn);
}
}
Embarassing! Props to Dweeberly for pointing it out. I just need to change the if statement from
if (el.AreaDesc.Value != null){}
to if (el.AreaDesc != null){}
Hi guys, probably a simple one.
Using C# .Net 4.0 and Visual Studio 2012 Ultimate.
Got the following code:
string part = "";
part = txtIOpart.Text;
txtBatchCV.Text = txtBatchIO.Text;
txtPartCV.Text = part;
txtExternalCV.Text = Sqlrunclass.SplitSpec_External(part, pg);
txtInternalCV.Text = Sqlrunclass.SplitSpec_Internal();
txtABSCV.Text = Sqlrunclass.SplitSpec_cvABS();
txtOilCV.Text = Sqlrunclass.SplitSpec_OilSeal();
txtBarCV.Text = "*" + Sqlrunclass.SplitInfo_ASno(part, pg) + "*";
txtBarNumCV.Text = txtBarCV.Text;
txtLocnCV.Text = Sqlrunclass.SplitInfo_Location();
txtFitsCV.Text = Sqlrunclass.SplitInfo_Desc();
txtHeightCV.Text = Sqlrunclass.SplitSpec_Height();
txtDiameterCV.Text = Sqlrunclass.SplitSpec_Diameter();
txtCirclitCV.Text = Sqlrunclass.SplitSpec_Circlit();
picTypeCV.Image = ftpclass.Download("CVspecType" + Sqlrunclass.SplitSpec_TypeCV() + ".jpg", "ftp.shaftec.com/Images/TypeJpg", "0095845|shafteccom0", "4ccc7365d4");
if (txtBatchCV.Text == null || txtBatchCV.Text == "")
{
txtBatchCV.Text = "ALL";
}
As you can see at the bottom I'm checking the batch, but I need to check all of the data thats being set by a bunch of methods. Each one will have a different txt output if it sees a null or blank txt. Is there anyway to shorten this code?
Try, txtBatchCV.Text For example
//Just for null
txtBatchCV.Text = (txtBatchCV.Text ?? "ALL").ToString();
//for both null and empty string
txtBatchCV.Text = string.IsNullOrEmpty(txtBatchCV.Text) ? "ALL": txtBatchCV.Text;
You could iterate through all the textboxes
foreach (var txt in form.Controls.OfType<TextBox>())
{
switch(txt.Id){
case "txtBatchCV":
// Do whatever you want for txtBatchCV e.g. check string.IsNullOrEmpy(txt.Text)
break;
}
}
I borrowed the above from here:
How do I loop through all textboxes and make them run corresponding actions from action dictionary?
In response to the comment I got from Tim, I've added a bit more code to explain what you could do. My code example was never meant to be a full solution.
TextBox.Text is never null, it will return "" then. If your methods return null you could use the null-coalescing operator:
string nullRepl = "ALL";
txtExternalCV.Text = Sqlrunclass.SplitSpec_External(part, pg) ?? nullRepl;
txtInternalCV.Text = Sqlrunclass.SplitSpec_Internal() ?? nullRepl;
txtABSCV.Text = Sqlrunclass.SplitSpec_cvABS() ?? nullRepl;
txtOilCV.Text = Sqlrunclass.SplitSpec_OilSeal() ?? nullRepl;
txtLocnCV.Text = Sqlrunclass.SplitInfo_Location() ?? nullRepl;
txtFitsCV.Text = Sqlrunclass.SplitInfo_Desc() ?? nullRepl;
txtHeightCV.Text = Sqlrunclass.SplitSpec_Height() ?? nullRepl;
txtDiameterCV.Text = Sqlrunclass.SplitSpec_Diameter() ?? nullRepl;
txtCirclitCV.Text = Sqlrunclass.SplitSpec_Circlit() ?? nullRepl;
For starters you could use string.IsNullOrEmpty(txtBatchCV.Text), it's a convevience method that basically does what you do in the if check.
You can atleast use one of these methods:
string.IsNullOrEmpty(txtBatchCV.Text)
or
string.IsNullOrWhitespace(txtBatchCV.Text)
I would try something like this:
void SetDefaultIfNull(TextBox txt, string defaultVal)
{
if (string.IsNullOrWhitespace(txt.Text))
txt.Text = defaultVal;
}
Then pass each textbox and the default to the method.
I'm parsing XML. I normally parse it the way I show in the code below which is straightforward The problem is that I don't own the XML I'm parsing and I can't change it. Sometimes there is no thumbnail element (there are no tags) and I get an Exception.
Is there a way to maintain this simplicity and check if the element exists? Or do I have to get first an XElement list with LINQ, to then check it and fill only the existing object properties?
void wc_DownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e)
{
XDocument dataDoc = XDocument.Load(new StringReader(e.Result));
var listitems = from noticia in dataDoc.Descendants("Noticia")
select new News()
{
id = noticia.Element("IdNoticia").Value,
published = noticia.Element("Data").Value,
title = noticia.Element("Titol").Value,
subtitle = noticia.Element("Subtitol").Value,
thumbnail = noticia.Element("Thumbnail").Value
};
itemList.ItemsSource = listitems;
}
[Edit]Jon Skeet's answer should be the accepted answer. It is far more readable and easier to apply.[/edit]
Create an extension method like this :
public static string TryGetElementValue(this XElement parentEl, string elementName, string defaultValue = null)
{
var foundEl = parentEl.Element(elementName);
if (foundEl != null)
{
return foundEl.Value;
}
return defaultValue;
}
then, change your code like this :
select new News()
{
id = noticia.TryGetElementValue("IdNoticia"),
published = noticia.TryGetElementValue("Data"),
title = noticia.TryGetElementValue("Titol"),
subtitle = noticia.TryGetElementValue("Subtitol"),
thumbnail = noticia.TryGetElementValue("Thumbnail", "http://server/images/empty.png")
};
This approach allows you to keep a clean code with isolating the check of element presence. It also allow you to define a default value, which can be helpful
Instead of using the Value property, if you cast to string you'll just get a null reference instead:
void wc_DownloadStringCompleted(object sender,
DownloadStringCompletedEventArgs e)
{
XDocument dataDoc = XDocument.Load(new StringReader(e.Result));
var listitems = from noticia in dataDoc.Descendants("Noticia")
select new News()
{
id = (string) noticia.Element("IdNoticia"),
published = (string) noticia.Element("Data"),
title = (string) noticia.Element("Titol"),
subtitle = (string) noticia.Element("Subtitol"),
thumbnail = (string) noticia.Element("Thumbnail")
};
itemList.ItemsSource = listitems;
}
That uses the explicit conversion from XElement to string, which handles a null input by returning a null output. The same is true for all explicit conversions on XAttribute and XElement to nullable types, including nullable value types such as int? - you just need to be careful if you're using nested elements. For example:
string text = (string) foo.Element("outer").Element("inner");
will give a null reference if inner is missing, but will still throw an exception if outer is missing.
If you want a "default" value, you can use the null coalescing operator (??):
string text = (string) foo.Element("Text") ?? "Default value";
You could just use the System.Xml.Serialization.XmlSerializer to deserialize it from xml to an object. Then if the element doesn't exist the property of the object will just get it's default value.
Have a look here: http://msdn.microsoft.com/en-us/library/system.xml.serialization.xmlserializer.aspx
or the new path
https://learn.microsoft.com/en-us/dotnet/api/system.xml.serialization.xmlserializer
You may use the code below:
string content = item.Element("Content") == null ? "" : item.Element("Content").Value;