Adding Key, Value XML Element using C#

Question

I have a problem with adding an element to an XML file using C#. I have my App.config files somewhere in my diff directory. So I am using LINQ to retrieve the values I want and to set the value from TextBoxes.

<appSettings>
    <add key="Something" value="false" />
    <add key="UserName" value="user0001" />
    <add key="Password" value="123456" />
    <add key="Environment" value="" />
    <add key="DBUserName" value="DBname23" />
    <add key="DBPassword" value="12345678" />
</appSettings>

The above is my XML file. I am able to retrieve the values of UserName and Password and set it with the encrypted ones. The way I am doing is shown below:

var doc1 = XDocument.Load(appConfigFile1);

var list1 = from appNode in doc1.Descendants("appSettings").Elements()
            where appNode.Attribute("key").Value == "UserName"
            select appNode;
var list2 = from appNode in doc1.Descendants("appSettings").Elements()
            where appNode.Attribute("key").Value == "Password"
            select appNode;
var list3 = from appNode in doc1.Descendants("appSettings").Elements()
            where appNode.Attribute("key").Value == "DBUserName"
            select appNode;
var list4 = from appNode in doc1.Descendants("appSettings").Elements()
            where appNode.Attribute("key").Value == "DBPassword"
            select appNode;
var element1 = list1.FirstOrDefault();
var element2 = list2.FirstOrDefault();
var element3 = list3.FirstOrDefault();
var element4 = list4.FirstOrDefault();
element1.Attribute("value").SetValue(txtbox1);
element2.Attribute("value").SetValue(txtbox2);
element3.Attribute("value").SetValue(txtbox3);
element4.Attribute("value").SetValue(txtbox4);
doc1.Save(appConfigFile1);

The requirements are such that if one of the elements from the XML file is deleted, I should be able to create a same element with key and value.

Example: Please compare the above xml with the below:

<appSettings>
    <add key="HasUI" value="false" />
    <add key="Password" value="123456" />
    <add key="Environment" value="" />
    <add key="DBUserName" value="DBname23" />
    <add key="DBPassword" value="12345678" />
</appSettings>

Above the element Username is missing. So how can I create an XML element like <add key="UserName" value="" /> and set that to that same place in XML file?

The error I am getting when I load the XML file in C# is NullReferenceException.

Please help me.

Why does it have to be in order? I just XML poke on mine (I actually do mine with powershell for this) — jcolebrand
– jcolebrand, Commented Jul 24, 2012 at 21:16
do you want to change the app.config or just put a default value when you don't have a value in app.config? — Clueless
– Clueless, Commented Jul 24, 2012 at 21:18
@jcolebrand hey!! i dont need that to be in order..i have edited the question — user1410658
– user1410658, Commented Jul 24, 2012 at 21:20

Ted Spence · Accepted Answer · 2012-07-25 16:41:29Z

3

For goodness sake, anything you do more than once should be a function!

function UpdateOrCreateAppSetting(XMLDocument doc, string key, string value)
{
    var list = from appNode in doc.Descendants("appSettings").Elements()
            where appNode.Attribute("key").Value == key
            select appNode;
    var e = list.FirstOrDefault();

    // If the element doesn't exist, create it
    if (e == null) {
        e = doc.CreateElement("add")
        e.Attributes.Append("key", key);
        e.Attributes.Append("value", value);
        doc.Descendants("appSettings").AppendChild(e);

    // If the element exists, just change its value
    } else {
        e.Attribute("value").SetValue(value);
    }
}

Now call the function four times and you're good. ;)

edited Jul 25, 2012 at 16:41

answered Jul 24, 2012 at 22:45

Ted Spence

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3 Comments

Ted Spence Over a year ago

Fixed a typo in the function.

FaizanHussainRabbani Over a year ago

@TedSpence What if I want to use Xdocument?

Mark Berry Over a year ago

Per msdn.microsoft.com/en-US/library/…, the XmlAttributeCollection.Append method takes one parameter, a node of type XmlAttribute. But you're passing two strings. How? I don't see that as an override. Is that a different method?

Clueless · Accepted Answer · 2012-07-24 21:22:22Z

if you just want to put a default value when the app.config is not as you expect you can do something like that:

var doc1 = XDocument.Load(appConfigFile1);

                var list1 = from appNode in doc1.Descendants("appSettings").Elements()
                            where appNode.Attribute("key").Value == "UserName"
                            select appNode;
                var list2 = from appNode in doc1.Descendants("appSettings").Elements()
                            where appNode.Attribute("key").Value == "Password"
                            select appNode;
                var list3 = from appNode in doc1.Descendants("appSettings").Elements()
                            where appNode.Attribute("key").Value == "DBUserName"
                            select appNode;
                var list4 = from appNode in doc1.Descendants("appSettings").Elements()
                            where appNode.Attribute("key").Value == "DBPassword"
                            select appNode;
                // the values of missing elements are null so you can use the "??" operator                                               //hat put something else when you have null
                var element1 = list1.FirstOrDefault() ?? "your default value";
                var element2 = list2.FirstOrDefault() ?? "your default value";
                var element3 = list3.FirstOrDefault() ?? "your default value";
                var element4 = list4.FirstOrDefault() ?? "your default value";
                element1.Attribute("value").SetValue(txtbox1);
                element2.Attribute("value").SetValue(txtbox2);
                element3.Attribute("value").SetValue(txtbox3);
                element4.Attribute("value").SetValue(txtbox4);
                doc1.Save(appConfigFile1);

Sorry Buddy!! I want to change the appconfig.Not just put the defualt... My bad.... i am getting a Null reference Exception near element1.Attribute("value").SetValue(txtbox1);

Kelly Cline · Accepted Answer · 2012-07-24 21:22:56Z

0

The NullReference is coming at the

element1.Attribute("value").SetValue(txtbox1);

statement, is it not? The FirstOrDefault above has left element1 to be null. I think you want to test for null before accessing the Attribute property; failing that test, you can then supply your default.

answered Jul 24, 2012 at 21:22

Kelly Cline

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1 Comment

user1410658 Over a year ago

Yes...Absolutly thats what happening.... yes i am dng that... but i am checking that null in element1..in that condition i want to write a c# script which can add <add key="UserName" value="" /> attribute to that AppSettings

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