access-clickonce-activation-data-dotnet.md

title	Access ClickOnce activation data for .NET
description	Learn how to access ClickOnce activation data for .NET Core 3.1, .NET 5 and later.
ms.date	01/05/2026
ms.topic	how-to
helpviewer_keywords	activation data, ClickOnce for .NET 5+ file associations, ClickOnce for .NET 5+
author	mikejo5000
ms.author	mikejo
ms.subservice	deployment
monikerRange	>= vs-2022

Access ClickOnce activation data for .NET on Windows

Starting in the .NET 8.0 version of dotnet-mage, you can access ActivationData properties using environment variables. Using this version of dotnet-mage, you can programmatically:

• Discover the filename for activation based on a custom file association.
• Discover arguments used for activation in the appref-ms file.

The launcher reads the AppDomain.CurrentDomain.SetupInformation.ActivationArguments.ActivationData array and sets the appropriate environment variables if the array is non-empty.

Environment variables

The following environments variables are set:

• ClickOnce_ActivationData_Count

  If this variable exists, the value is the count of elements in ActivationData string array.

• ClickOnce_ActivationData_<n>

  For each element in array, a new environment variable gets added with a zero-based index, that is:

  ClickOnce_ActivationData_0 ClickOnce_ActivationData_1

  The scenarios fixed by this change always use the zero-index element, so the variable will always be ClickOnce_ActivationData_0, but the code is flexible and is able to pass all activation data to .NET app.

Access properties

You can read these environment variables to discover ActivationData content, using the following code:

string value = Environment.GetEnvironmentVariable("ClickOnce_ActivationData_0");

Previously, for .NET Framework apps, you would read this data using the following code:

string value = AppDomain.CurrentDomain?.SetupInformation?.ActivationArguments?.ActivationData?[0];

Related content

ClickOnce for .NET on Windows