How to reference third-party libraries in Unity? Should I use using directly?

A common way to reference third-party libraries in Unity is to useAssembly Definition Files（程序集定义文件）.

This is a mechanism provided by Unity that allows you to create your own assembly to reference and use third-party libraries in Unity projects. Here are some simple steps:

1. In the Unity Editor, right-click on your Assets folder and select Create > Assembly Definition.
2. Give the assembly definition file a name, such asMyLibrary.
3. Create a folder namedPlugins in Unity and put the DLL file of the third-party library into it.
4. Right-click the newly created assembly definition file and selectProperties.
5. In the list in the General section, click the button to add a citation. References+
6. Select the DLL file to be referenced and clickAdd.
7. Make sure the assembly definition file'sAuto Referenced option is checked to ensure that Unity automatically references the dependency when building.
8. ClickApply to save changes.

Now, you can use the using keyword in the script of the Unity project to reference the third-party library and use the types and functions in it.

Note that some third-party libraries may require additional setup or operations for correct use. Additionally, some third-party libraries may require platform-specific setup and import. Please read carefully the documentation of the third-party library you are using and follow its instructions.