Missing System.Windows.Forms Assembly in Telerik ReportViewer WPF on .NET 9
Environment
| Product | Progress® Telerik® Reporting |
| Operating System | Windows 10 |
| .NET Version | .NET 9 |
| Application Type | WPF |
Description
When deploying a WPF application with the Telerik ReportViewer component and upgrading to .NET 9, an error stating that the System.Windows.Forms assembly could not be loaded is encountered on the first launch of a print window. This issue does not occur on subsequent openings of the print window. This knowledge-base article also answers the following questions:
- How to fix the
System.Windows.Formsassembly loading error in Telerik ReportViewer WPF on .NET 9? - What is the solution for a missing
System.Windows.Formsassembly error when using Telerik ReportViewer WPF in a .NET 9 application? - How to ensure the Telerik ReportViewer WPF component loads correctly in .NET 9 on the first attempt?
Solution
To address the issue of the System.Windows.Forms assembly not loading during the first use of the Telerik ReportViewer WPF component in a .NET 9 application, especially when deployed via MSIX, add the UseWindowsForms property set to true in the main WPF project file. This ensures that the System.Windows.Forms dependencies are correctly referenced, allowing the Telerik ReportViewer to initialize without errors on its first load.
Modify the project file (.csproj) of your WPF application to include the following property:
<PropertyGroup>
<UseWindowsForms>true</UseWindowsForms>
</PropertyGroup>
This configuration explicitly informs the project that Windows Forms components are utilized, ensuring the necessary assemblies are available at runtime. This solution is particularly relevant for applications packaged with MSIX, where dependency management may differ from traditional deployment methods.