如果我能得到完整的项目就更好了。但我在这里建议几种方法：

方式1：

把behavior放在Activity类里面怎么样？示例化它onCreate()。然后像这样从ToolboxSheetFragment使用它。

class MainActivity : BaseActivity() {
    var behavior: BottomSheetBehavior? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        behavior = BottomSheetBehavior.from(R.id.sheet_id)
    }
}

然后从ToolboxSheetFragment

class ToolboxSheetFragment : Fragment(R.layout.fragment_toolbox_sheet) {
    private lateinit var binding: FragmentToolboxSheetBinding
    var behavior: BottomSheetBehavior? = null

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        binding = FragmentToolboxSheetBinding.bind(view)
        behavior = (requireActivity() as MainActivity).behavior
    }

方式二：

在ToolboxSheetFragment上使用addOnAttachStateChangeListener：

@AndroidEntryPoint
class ToolboxSheetFragment : Fragment(R.layout.fragment_toolbox_sheet) {
    private lateinit var binding: FragmentToolboxSheetBinding
    private lateinit var behavior: BottomSheetBehavior<View>

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        view.addOnAttachStateChangeListener(object : View.OnAttachStateChangeListener {
            override fun onViewAttachedToWindow(v: View?) {
                if(v!=null){
                    binding = FragmentToolboxSheetBinding.bind(v)
                    behavior = BottomSheetBehavior.from(
                        v.parent as View 
                    )
                }
            }

            override fun onViewDetachedFromWindow(v: View?) {
                view.removeOnAttachStateChangeListener(this)
            }

        })
    }

首先在onCreateView()中扩展布局，然后可以在onViewCreated()中完成所有与视图相关的工作。

override fun onCreateView(
    inflater: LayoutInflater,
    container: ViewGroup?,
    savedInstanceState: Bundle?
): View {
    binding = FragmentToolboxSheetBinding.inflate(layoutInflater)
    return binding.root
}

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)
    behavior = BottomSheetBehavior.from(view)
}

请不要忽略savedInstanceState，并确保Fragment甚至连接到任何Context。抱歉，没有提供功能完整的答案;例如，onAttached()可以确定Fragment是附加的-并且savedInstanceState可能是也可能不是null。并且当view.parent为空时，View可能不存在，它可能是MainActivity的behavior，而不是ToolboxSheetFragment，这不是一回事。