Use Query String
ClickOnce applications can be installed from a website, and they can also be invoked from a webpage. All that's needed is a hyperlink that references the .application file, e.g.: http://www.mywebsite.com/foobar/foobar.application. When user clicks the link, Foobar will launch (actually, the same link will install Foobar on user machine). In this scenario, parameters can be passed to the application by adding query string to the URL: http://www.mysite.com/foobar/foobar.application?param1=value1¶m2=value2&... . Here's how to do it:
Step 1: Enable URL parameters in ClickOnce application
Open project properties in Visual Studio and click "Publish" tab. Then click "Options" button, which brings up a dialog window. Select "Manifests" from the list, and make sure the checkbox that reads "Allow URL parameters to be passed to application" is checked.
Step 2: Add code to process parameters
In regular Windows applications written in C#, it is enough to declare static void Main(string args) in order to get the list of command line parameters in the args array. Unfortunately, this doesn't work with ClickOnce applications - the args array will be empty whether or not URL had any parameters. In order to access them, we need to analyze AppDomain.CurrentDomain.SetupInformation.ActivationArguments.ActivationData property.
static void Main()
var args = AppDomain.CurrentDomain.SetupInformation.ActivationArguments;
var frm = new MainForm();
if (args != null
&& args.ActivationData != null
&& args.ActivationData.Length > 0)
var url = new Uri(args.ActivationData, UriKind.Absolute);
var parameters = HttpUtility.ParseQueryString(url.Query);
// Process parameters here
Add File Type Association
Another interesting approach is to associate the application with a specific file extension. When a file with this extension is downloaded from a web page or opened in Windows Explorer, application will be launched automatically and file name will be passed to it. Prior SP1 release of .NET 3.5, file type association had to be created programmatically (by creating subkeys for the desired extension and a shell\open\command using Microsoft.Win32.Registry API). Visual Studio 2008 SP1 allows to define association declaratively. In the same Options dialog mentioned above, click "File Associations" and fill in required information in the data grid.
Processing logic is very similar to the first scenario - we still need to analyzeAppDomain.CurrentDomain.SetupInformation.ActivationArguments.ActivationDataproperty. The only difference is that instead of calling HttpUtility.ParseQueryString, we need to extract file name from it.