Why Does My C# Generic Numeric Helper Class Fail in Published Builds but Work in Debug Mode?

Below is one likely explanation and solution for the issue.

---

Cause

When you run the app in Debug mode the reflection calls (for example, calling GetField("MinValue") on a built‐in numeric type) work normally. However, in a published (especially WebAssembly) build the linker (IL trimmer) may remove members that only appear to be used via reflection. In your generic class the code:

CSHARPCopied
var fieldInfo = Type.GetField(fieldName);

may return null for types like Int32 even though those fields exist. This happens because the trimmer removed them as “unused” members. The subsequent use of these fields can then lead to runtime errors that manifest as the “no element is currently associated with component 250” error when the component’s rendering process fails.

---

Recommendations for Fixing

1. Preserve the reflective members:
   Use linker XML files or attributes (such as [DynamicDependency] or [RequiresUnreferencedCode] in some cases) to tell the linker to keep the specific members (e.g. MinValue, MaxValue) for the numeric types you expect to use.

2. Disable trimming (if acceptable):
   Alternatively, if trimming is not needed, you can disable it by setting the publish trimming property in your project file:

   XMLCopied
   <PropertyGroup>
     <PublishTrimmed>false</PublishTrimmed>
   </PropertyGroup>

3. Explicitly reference the fields:
   Another approach is to add a dummy reference to those fields somewhere in your code so that the linker knows they are used. For example:

   CSHARPCopied
   // This static method makes an explicit reference that prevents trimming.
   public static void PreserveNumericMembers()
   {
       var _ = int.MinValue;
       _ = int.MaxValue;
   }

   Call this method somewhere during app startup.

---

Summary

The error is likely due to IL trimming in the publish build removing members referenced only by reflection (such as MinValue and MaxValue). In order to fix it, preserve those members (via appropriate linker configuration or attributes) or disable trimming if it works for your scenario.

Ensure that after making these changes you retest the published version since the behavior under the IL trimmer may differ from Debug builds.