How can you retrieve the value of a Query String parameter in an ASP.NET web page?

In ASP.NET, you can retrieve the value of a query string parameter in an ASP.NET web page using the 'Request.QueryString' collection. The 'Request.QueryString' collection provides access to the query string parameters and their corresponding values.

To retrieve the value of a specific query string parameter, you can use the indexer syntax 'Request.QueryString["parameterName"]', where "parameterName" is the name of the parameter you want to retrieve.

Here's an example that demonstrates how to retrieve the value of a query string parameter named "id":

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

    // Use the retrieved value as needed
    // e.g., display it on the page or perform operations based on the value
}

In this example, the value of the "id" parameter from the query string will be stored in the id variable. You can then use the retrieved value to perform any necessary operations, such as displaying it on the page or utilizing it for further processing.

It's important to note that the query string parameter names are case-sensitive. So make sure to use the correct parameter name when accessing values from the 'Request.QueryString' collection.

Additionally, it's a good practice to check for null or empty values when retrieving query string parameters. You can use conditional statements or methods like 'String.IsNullOrEmpty()' to handle cases where the parameter value is not provided in the URL or is empty.

string id = Request.QueryString["id"];
if (!String.IsNullOrEmpty(id))
{
    // Process the value
}
else
{
    // Handle the case where the parameter is not provided
}

By retrieving and processing query string parameters, you can dynamically customize the behavior or content of your ASP.NET web pages based on the values passed in the URL.