PRB: Error When You Access .resources File of the Form at Run Time

When you are running your Visual Basic .NET, Visual C# .NET, or Visual J# .NET Windows application, you may receive the following error message or a similar one when you load a form: If you click Break in the error dialog box, and if you are running the code in the integrated development environment (IDE), you discover that a line of code inside the InitializeComponent statement causes this problem. For example, if you create the sample from the "More Information" section, this error occurs in conjunction with an ImageList control. Although the error message may refer to a different control, notice that resources.GetObject appears on that line of code in the error message:

This problem occurs because the Form class is not the first class in the code module of the form.

NOTE: This article documents one specific cause of this problem. There may be other situations that can lead to similar results.

To resolve this problem, move all of the other class definitions so that they appear after the form's class definition.

This behavior is by design.

A form code module can contain multiple classes. When the project is built, the build system must decide which class it should use to create the .resources file. The design of the project build system specifies that the first class in the code module is the class on which the .resources file is based. The .resources file is named according to that class, not the name of the form. In most cases, these two names are the same. However, if these names differ, you receive the error message that is listed in the "Symptoms" section.

When you load the form at run time, the InitializeComponent method may need to get objects from the .resources file. InitializeComponent searches for the Form_Name.resources file in the assembly. Because the initial Form_Name.resources file was never created or linked to the assembly, the attempt to retrieve the .resources file fails.

Steps to Reproduce the Behavior

1.	Create a Windows Application project in Visual Basic .NET, Visual C# .NET, or Visual J# .NET. Form1 is created by default.
2.	Add an ImageList control to Form1.
3.	Add an icon file to the ImageList control.
4.	In the code module of Form1, add the following code before the Form1 definition: Visual Basic .NET: Public Class someClass End Class Visual C# .NET and Visual J# .NET: public class someClass { }
5.	Build the project. Notice that the project builds successfully.
6.	Run the project. Notice that you receive the error message that is listed in the "Symptoms" section.