C# Code: Duncan’s C# string tester for value. Particularly useful for ASP.NET.

This is an old post from old blog but google keeps sending people here so I figured I’d backfill it in.

(Examples in C# but easy to do in VB.NET)

If you are slinging ASP.NET for a living or just dealing with lots of string inputs in general, you’ve undoubtedly thought about how you are going to test to make sure your strings have value to them. Lets say you have some querystring parameter that is required for your page to do anything meaningful. So what are you looking to test?

You want to make sure:

1) The string coming in is not null.
2) The trimmed value of the string (providing it is indeed not null) is more than just blank.

Looking to the standard API, you may be tempted to use the built-in String.Empty.

What’s wrong with this seemingly-perfect native method? A small but important item, when it checks for an empty string, there is no trimming involved. In the real world we really never want an input with leading or trailing spaces, and certainly don’t want to accept just a space. Sadly, we can’t pre-trim our string before calling this method as if we do have a null in our hands we will throw and exception trying to trim nothingness.

Ok, next step lets write a couple simple lines of code to test the string ourselves.

Following the FxCop recommendations and good computing sensibilities you’ll find it is cheapest to do the following logic as opposed to say, checking for == “” which is ungood. (C#)

if (stringToTest != null &&
stringToTest.Trim().Length > 0)
{
// its ok!
}

I had this snippet all over the place in my code but was always annoyed that once passing our conditions, including the trim, I had to trim the string anyway inside of the block before I did anything useful with it. What I really wanted was two things at once, to make sure my criteria was met, and if so, to have the “fixed” string in my hand ready to go. Enter the ref. Here is a example of an ASP code-behind calling a helper method StringHasValue that makes life a little easier. In practice, I tuck the StringHasValue method away in a StringUtilities.cs class.

protected void Page_Load(object sender, EventArgs e){
string myString = Request["someParam"];

if (StringHasValue(ref myString))
{
// do things that depend on a myString having a value
// and myString being nicely trimmed.
// such as ….

Literal1.Text = “:” + myString + “:”; // show we are trimmed

}
else
{
Literal1.Text = “Sorry, have no value to speak of”;
}

}

private static bool StringHasValue(ref string stringToTest)

{

bool isOK = false;
if (stringToTest != null &&
stringToTest.Trim().Length > 0)

{
isOK = true;
stringToTest = stringToTest.Trim();
}

return isOK;

}

Now once I’m in my block, having tested if the string has a value, I’m ready to rock with my string and get down to the business at hand. No trimming, no worries. Having StringHasValue as a nice one-liner also lets me simply evaluate a number of params at once with some && action, with all of my strings ready to go.

string myString = Request["someParam"];
string myStringTwo = Request["someParamTwo"];
string myStringThree = Request["someParamThree"];
string myStringFour = Request["someParamFour"];

if (StringHasValue(ref myString) &&
StringHasValue(ref myStringTwo) &&
StringHasValue(ref myStringThree) &&
StringHasValue(ref myStringFour)
)

{
// do stuff
}

Ok, passing values by ref and then acting upon them can be slightly tricky in complex methods as you run the risk of not being able to follow future code, scratching your head wondering how the heck some value gets assigned. I feel in this case though the simplicity of the operation, and a well-named method can make this a pretty reasonable option.