How to use a UriBuilder and HttpUtility.ParseQueryString to store a URL and parse it

Question

What I'm trying to do is use an UriBuilder and HttpUtility.ParseQueryString to get the last page the user visited and then parse the URL to get just the productID. (The product ID is different on each page if that matters)

example URL: website.com/stuff/?referrerPage=1&productID=1234567&tab=Tile

and what I want is just the 1234567

Page_Load is where I parse the URL:

protected void Page_Load(object sender, EventArgs e) 
{ 
    NameValueCollection query = HttpUtility.ParseQueryString(uriBuilder.Query);
    //I want to take the parse string and get productID here, how?
} 

grabURL is where I get the last URL visited:

public grabUrl(string Uri) 
{ 
    UriBuilder uriBuilder = new UriBuilder(Request.UrlReferrer); 
    return uriBuilder.Uri; 
}

Am I on the right track with my code? How do I put the productID number in something so I can work with it? I'm very new to c# and this type of coding in general... when I say new I mean I've been doing it for about a week. So any detailed explanations or examples will be very much appriciated. Thanks everyone for being so helpful, I'm learning a lot from this site to get me on the right track.

Answer 1

From a NameValueCollection you can then do:

var id = query["ProductID"];

You can use int.TryParse to turn it into an integer proper.

int id = 0;
if (!string.IsNullOrEmpty(query["ProductID"]) && 
  int.TryParse(query["ProductID"], out id))  {
  // use id here..
}

Answer 2

Or you could just request the querystring value from your URL using Request.QueryString()

protected void Page_Load() 
{ 
    //save yourself the conversion to int and just save it as Int if you know for sure
    // it will always be int
    int _prodID= Request.Querystring["productID"];
    //validate _prodID
    if (!string.IsNullOrEmpty(_prodID.toString())) {//do something }
}

Answer 3

Could you use a regex to parse it instead?

string uri = "website.com/stuff/?referrerPage=1&productID=1234567&tab=Tile";
var rgx = new Regex("productID=(?<pid>[0-9]+)", RegexOptions.IgnoreCase);
string pid = rgx.Match(uri).Groups[1].Value;

Edit: Providing context as it has been suggested I should do:

The reason for mentioning this option is that while it doesn't use HttpUtility.ParseQueryString, your original question was very specific:

get just the productID

from

the last page the user visited

(which I understand to not be the uri of the current request). Additionally you provided the Uri was provided in a string format.

The approach in your question does this:

• Takes Uri (a string variable)
• Passes it to UriBuilder; UriBuilder in its constructor initialises a Uri, which itself does a ton of work to validate the uri, populate properties etc. by creating more strings, among other things
• Then, from the Uri object generated, you now work with the Query property - this is one of the new strings that Uri has allocated
• Passes that to HttpUtility.ParseQueryString. This creates a HttpValueCollection, which itself iterates character-by-character over the string you pass in to parse out the key-value pairs in the query string, and sticks them into a NameValueCollection, which ultimately stores your values in an ArrayList - one of the least efficient collections in .NET (see various references including this one - What's Wrong with an ArrayList?) as it stores everything in an object array, requiring casting every time you get things back out.
• finally you then go and search that collection by a key to get your product id back out.

That's a whole lot of string and character allocations, casting to and from objects, putting things into indexed arrays which you then scan, etc. just to get:

• a string which is identifiable by a pattern from another string.

While I admit that memory is cheap, it seems that there might be an equally good, or better, alternative. This is what regex was made for - find a pattern in a string, and allow you to get parts of that pattern back out.

So, your options:

1. If you just want to get productID out of a uri in an exact form, and the uri is originally in a string, then I maintain that a regex is a very good, efficient choice. This will also work if you want to extract other patterns from your uri.
2. If you want to know all the keys in your query string as well as values for specific keys, then use your HttpUtility.ParseQueryString approach; NameValueCollection allows you to get access to the keys through the AllKeys property.
3. If you want to get the value of a query string parameter for the uri of your current request then Marcianin's answer is the simplest choice, and you can forget the first 2 options.

In all cases, once you have the string you can parse it using the parse methods on int, but if you use 2. or 3. your extracted id may not be a number (in the case of a malicious request) so make sure you use int.TryParse not int.Parse to convert from a string, and be careful to catch exceptions. You should always take care when taking input from query strings so as not to fall foul of malicious data in the query string (which will hit your website frequently once it is online).

The choice is personal preference.

• The actual code you write is about the same - each approach takes up very few lines.
• Code should never prematurely optimise, but it should also not be deliberately wasteful if it can help it. You could performance test one against the other, but that would be a waste of your time at this stage.
• However, code should also convey intent. The Regex approach, even I would argue, doesn't convey your intent as well as the ParseQueryString approach.

Footnote: I would change the regex slightly to "[?&]productID=(?<pid>[0-9]+)" to ensure you pick up only "productID" and not "fooProductID"

Most importantly, you asked

Am I on the right track with my code?

I would say you are. Always weigh up different options as you proceed. Don't be afraid to try different things out. You say you are new to C#. The one thing you may have missed, in this case, is writing a test to help you on your way before you wrote your code: if the test passes, the code is correct, and the approach you chose is secondary to that. Visual Studio makes testing easy for you if you are using the latest version. If you get into good habits early on, it will pay dividends later on in your C# career.

How do I put the productID number in something so I can work with it?

Grant Thomas answered this perfectly - int.TryParse turns the string into a number.