Daniel Waltrip Daniel Waltrip - 1 year ago 148
C# Question

C# How can I check if a URL exists/is valid?

I am making a simple program in visual c# 2005 that looks up a stock symbol on Yahoo! Finance, downloads the historical data, and then plots the price history for the specified ticker symbol.

I know the exact URL that I need to acquire the data, and if the user inputs an existing ticker symbol (or at least one with data on Yahoo! Finance) it works perfectly fine. However, I have a run-time error if the user makes up a ticker symbol, as the program tries to pull data from a non-existent web page.

I am using the WebClient class, and using the DownloadString function. I looked through all the other member functions of the WebClient class, but didn't see anything I could use to test a URL.

How can I do this?

Answer Source

You could issue a "HEAD" request rather than a "GET"?

(edit) - lol! Looks like I've done this before!; changed to wiki to avoid accusations of rep-garnering. So to test a URL without the cost of downloading the content:

// using MyClient from linked post
using(var client = new MyClient()) {
    client.HeadOnly = true;
    // fine, no content downloaded
    string s1 = client.DownloadString("http://google.com");
    // throws 404
    string s2 = client.DownloadString("http://google.com/silly");

You would try/catch around the DownloadString to check for errors; no error? It exists...

With C# 2.0 (VS2005):

private bool headOnly;
public bool HeadOnly {
    get {return headOnly;}
    set {headOnly = value;}


using(WebClient client = new MyClient())
    // code as before
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