Issue: Unable to Access Class from App_Code Folder in ASP.NET Web Application

Description:

I have developed a website using ASP.NET and added a class file inside the App_Code folder. However, I am unable to access this class from other pages within the project. I’ve successfully implemented a similar structure in previous projects without issues, so I’m unsure what might be causing the problem in this case. Is there a specific configuration required to enable this?

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Primary Solution: Check Build Action

1. Right-click the .cs file located in the App_Code folder.

2. Select Properties.

3. Ensure the "Build Action" is set to "Compile".
   This allows the class to be compiled and made available throughout the application.

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Additional Solutions:

2. Verify the File Is in a Web Application Project (Not Web Site Project)

• App_Code is typically used in Web Site Projects, not Web Application Projects.

• If you are using a Web Application Project, classes should be placed in regular folders (like Models or Helpers), and included in the .csproj file.

3. Check the Class Accessibility

• Ensure your class is declared as **public** so it can be accessed from other parts of your application:

  public class MyClass
  {
      // Class members
  }

4. Clean and Rebuild the Project

• Sometimes, build inconsistencies can cause this issue.

  • Clean the solution: Build > Clean Solution

  • Rebuild: Build > Rebuild Solution

5. Check Namespace Declarations

• Ensure you're using the correct using directive at the top of your page:

  using YourNamespaceName;
  

6. Confirm There Are No Compilation Errors

• A compile error elsewhere in the App_Code folder may prevent the entire folder from compiling, causing all classes within to be inaccessible.

7. Verify Target Framework Compatibility

• Ensure the project’s target .NET Framework is appropriate and consistent with the class code.

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Let me know if you'd like help identifying whether your project is a Web Site or Web Application type, or if you want assistance migrating code between them.