Question

How to check if the web page contains any string queries at the page load?

Answer 1

You can determine if there are any values in the QueryString by checking its count:

Request.QueryString.Count > 0;

That said if you are trying to prevent a page from erroring because you don’t want to access a value that is not there I recommend wrapping query parms up in page properties and returning safe values from the property.

As an example

// setting this as protected makes it available in markup
protected string TaskName
{
    get { return (string)Request.QueryString["VarName"] ?? String.Empty; }
}