Why Does My Code Throw a TypeLoadException Even Though the Method Is Implemented?

Deep exploration: TypeLoadException exception, the method is obviously implemented but the prompt is missing

Target:

Identify the root cause of the TypeLoadException exception indicating that a method is missing when in fact it exists.

Question:

The test machine threw the following error:

<code>System.TypeLoadException: 类型 'DummyItem' 中的方法 'SetShort'（来自程序集 'ActiveViewers (...)'）没有实现。</code>

Reason:

The error results from an outdated interface assembly version being referenced during the build process of the implementation assembly.

Technical explanation:

1. Interface based implementation: In this example, the 'DummyItem' class implements an interface in another assembly.
2. Version differences: The 'SetShort' method has recently been added to interface and implementation classes. However, when the implementation assembly is rebuilt, the newer version of the interface assembly is not referenced.
3. Missing link: Therefore, the 'SetShort' method exists in the implementation class, but the corresponding implementation is missing in the referenced interface assembly. Therefore, TypeLoadException exception is thrown.

Solution:

1. Clean and Rebuild: Remove all 'bin' and 'obj' directories and rebuild all assemblies. This ensures that the correct DLL version is used.
2. Correct interface reference: Ensure that during the rebuild process, the implementation assembly references the latest version of the interface assembly. This links the 'SetShort' method in the implementing class with its equivalent method in the interface.

Demo:

To reproduce the issue:

1. Create an interface assembly that contains the 'GetString' method.
2. Create an implementation class library that references the interface assembly and contains the 'GetString' method.
3. Create a client application that references both assemblies and calls the 'GetString' method.
4. Run the application and verify the behavior.
5. Add new 'GetShort' method in interface and implementation assemblies.
6. Rebuild the implementation assembly without referencing the updated interface assembly.
7. Update client application with new DLL and rebuild.
8. Run the client application and observe the TypeLoadException exception for 'GetShort'.

Additional Tips:

• Check the assembly version number to ensure correct references.
• Use dependency management tools to track assembly dependencies.
• Use logging mechanism to identify version inconsistencies.

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