CODEWITHSUNDEEP
c#asp.net.net-3.5
Aaron Blenkush
Aaron Blenkush

Reputation: 3059

Check if unassigned variable exists in Request.QueryString

Within the context of an ASP.NET page, I can use Request.QueryString to get a collection of the key/value pairs in the query string portion of the URI.

For example, if I load my page using http://local/Default.aspx?test=value, then I can call the following code:

//http://local/Default.aspx?test=value

protected void Page_Load(object sender, EventArgs e)
{
    string value = Request.QueryString["test"]; // == "value"
}

Ideally what I want to do is check to see if test exists at all, so I can call the page using http://local/Default.aspx?test and get a boolean telling me whether test exists in the query string. Something like this:

//http://local/Default.aspx?test

protected void Page_Load(object sender, EventArgs e)
{
    bool testExists = Request.QueryString.HasKey("test"); // == True
}

So ideally what I want is a boolean value that tell me whether the test variable is present in the string or not.

I suppose I could just use regex to check the string, but I was curious if anybody had a more elegant solution.

I've tried the following:

//http://local/Default.aspx?test

Request.QueryString.AllKeys.Contains("test"); // == False  (Should be true)
Request.QueryString.Keys[0];                  // == null   (Should be "test")
Request.QueryString.GetKey(0);                // == null   (Should be "test")

This behavior is different than PHP, for example, where I can just use

$testExists = isset($_REQUEST['test']); // == True

Upvotes: 20

Views: 25263

Answers (7)

Elias
Elias

Reputation: 53

Visual Basic Solution

Request.QueryString.GetValues(vbNullString).Contains("test")

Although @Joe's answer is the correct answer, it doesn't account for VB.net programmers. The VB issue with @Joe's [correct] answer is that it yields an error at the "GetValues(null)" section. vbNullString alleviates the issue.

Additional Note

ClientQueryString.Contains("test")

might solve your problem (it did for me). Please know, though, that this solution has its pitfalls.

Summary for VB Programmers

Either of these will [probably] get the job done for you:

  1. Request.QueryString.GetValues(vbNullString).Contains("test")
  2. ClientQueryString.Contains("test")

I would've added this as a comment, but I don't have enough reputation points (43 out of 50)

Upvotes: 1

Abdul Khaliq
Abdul Khaliq

Reputation: 2285

TRY this one, it solved my issue! It will count either the query string has a value or empty and then you can check the required query string value with the Key.

  if (!Page.IsPostBack)
        {
           if (Request.QueryString.Count > 0)
            {
                if (Request.QueryString["departmentId"] != null)
                {
                    GetSurveyByDeptAndStatus(departmentId: Request.QueryString["departmentId"], status: "Not Surveyed");
                    rbListEmpsSurvey.Items[1].Selected = true;
                }

                else if (Request.QueryString["SurveyStatus"] != null)
                {
                    SatisfactionStatus = Request.QueryString["SurveyStatus"] "";
                    GetSurveyByDeptAndStatus(status: SatisfactionStatus);
                    GetDepartments();
                }}}

Upvotes: 1

Dtagg
Dtagg

Reputation: 78

I use this.

if (Request.Params["test"] != null)
{
    //Is Set
}
else if(Request.QueryString.GetValues(null) != null && 
       Array.IndexOf(Request.QueryString.GetValues(null),"test") > -1)
{
    //Not set
}
else
{
    //Does not exist
}

Upvotes: 2

GlennG
GlennG

Reputation: 3000

Request.QueryString.ToString().Contains("test")

This works in the special case where you're looking for a single querystring parameter, e.g. MyFile.aspx?test

For more complex, general, cases then other solutions would be better.

Upvotes: -2

Oren Melzer
Oren Melzer

Reputation: 760

Request.QueryString is a NameValueCollection, but items are only added to it if the query string is in the usual [name=value]* format. If not, it is empty.

If your QueryString was of the form ?test=value, then Request.QueryString.AllKeys.Contains("test") would do what you want. Otherwise, you're stuck doing string operations on Request.Url.Query.

Upvotes: 2

Dark Daskin
Dark Daskin

Reputation: 1474

I wrote an extension method to solve this task:

public static bool ContainsKey(this NameValueCollection collection, string key)
{
    if (collection.AllKeys.Contains(key)) 
        return true;

     // ReSharper disable once AssignNullToNotNullAttribute
    var keysWithoutValues = collection.GetValues(null);
    return keysWithoutValues != null && keysWithoutValues.Contains(key);
}

Upvotes: 5

Joe
Joe

Reputation: 5487

Request.QueryString.GetValues(null) will get a list of keys with no values

Request.QueryString.GetValues(null).Contains("test") will return true

Upvotes: 29

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