如何从Fragment打开DialogFragment并实现回调数据传递？

我是一名大学生，此前在示例应用中通过回调实现了从MainActivity打开DialogFragment并返回数据，但现在尝试从Fragment打开该DialogFragment时，回调仍指向MainActivity而非发起的Fragment。请问能否通过回调实现需求？若不行，改用Navigation参数需要做哪些修改？我已附上在Activity中可行的代码示例，此前查资料了解到可通过Navigation参数实现，但对此不太理解。

class MenuFragment : Fragment(), PlanAdapter.PlanItemClickListener, PlanItemDialogFragment.NewPlanItemDialogListener {
    private lateinit var binding : FragmentMenuBinding

    private lateinit var database: PlanListDatabase
    private lateinit var adapter: PlanAdapter

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

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

        database = PlanListDatabase.getDatabase(requireActivity().applicationContext)

        binding.fab.setOnClickListener{
            PlanItemDialogFragment().show(
                childFragmentManager,
                PlanItemDialogFragment.TAG
            )
        }
    }
}

class PlanItemDialogFragment : DialogFragment() {
    interface NewPlanItemDialogListener {
        fun onPlanItemCreated(newItem: PlanItem)
    }

    private lateinit var listener: NewPlanItemDialogListener

    private lateinit var binding: DialogNewItemBinding

    override fun onAttach(context: Context) {
        super.onAttach(context)
        listener = context as? NewPlanItemDialogListener
            ?: throw RuntimeException("Activity must implement the NewPlanItemDialogListener interface!")
    }

    override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
        binding = DialogNewItemBinding.inflate(LayoutInflater.from(context))

        return AlertDialog.Builder(requireContext())
            .setTitle(hu.bme.aut.android.mobil_hf.R.string.new_plan_item)
            .setView(binding.root)
            .setPositiveButton(hu.bme.aut.android.mobil_hf.R.string.button_ok) { dialogInterface, i ->
                if (isValid()) {
                    listener.onPlanItemCreated(getPlanItem())
                }
            }
            .setNegativeButton(hu.bme.aut.android.mobil_hf.R.string.button_cancel, null)
            .create()
    }
}

一、通过回调实现需求的修改方法 #

可以用回调实现，问题出在PlanItemDialogFragment的onAttach方法里直接把context（此时是Activity）强转为监听器。只需让DialogFragment直接接收发起的Fragment作为监听器即可，修改步骤如下：

1. 修改PlanItemDialogFragment #

class PlanItemDialogFragment : DialogFragment() {
    interface NewPlanItemDialogListener {
        fun onPlanItemCreated(newItem: PlanItem)
    }

    private var listener: NewPlanItemDialogListener? = null

    // 新增静态方法传入监听器
    companion object {
        const val TAG = "PlanItemDialogFragment"
        fun newInstance(listener: NewPlanItemDialogListener): PlanItemDialogFragment {
            val fragment = PlanItemDialogFragment()
            fragment.listener = listener
            return fragment
        }
    }

    override fun onAttach(context: Context) {
        super.onAttach(context)
        // 若未传入监听器，再尝试从Activity获取（兼容原来的逻辑）
        if (listener == null) {
            listener = context as? NewPlanItemDialogListener
                ?: throw RuntimeException("Activity or Fragment must implement NewPlanItemDialogListener!")
        }
    }

    override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
        binding = DialogNewItemBinding.inflate(LayoutInflater.from(context))

        return AlertDialog.Builder(requireContext())
            .setTitle(hu.bme.aut.android.mobil_hf.R.string.new_plan_item)
            .setView(binding.root)
            .setPositiveButton(hu.bme.aut.android.mobil_hf.R.string.button_ok) { _, _ ->
                if (isValid()) {
                    listener?.onPlanItemCreated(getPlanItem())
                }
            }
            .setNegativeButton(hu.bme.aut.android.mobil_hf.R.string.button_cancel, null)
            .create()
    }
}

2. 修改MenuFragment中打开Dialog的代码 #

binding.fab.setOnClickListener{
    val dialog = PlanItemDialogFragment.newInstance(this)
    dialog.show(childFragmentManager, PlanItemDialogFragment.TAG)
}

这样监听器就会绑定到发起的MenuFragment，而非Activity。

二、改用Navigation参数的修改方法 #

如果不想用回调，Navigation组件的SavedStateHandle可以更优雅地实现数据返回，步骤如下：

1. 确保PlanItem实现Parcelable接口 #

Navigation参数要求数据可序列化，给PlanItem添加Parcelable实现：

@Parcelize
data class PlanItem(
    // 你的实体字段，比如id、title等
) : Parcelable

2. 在导航图（nav_graph.xml）中添加DialogFragment #

将PlanItemDialogFragment添加为dialog类型的目的地：

<dialog
    android:id="@+id/planItemDialogFragment"
    android:name="你的包名.PlanItemDialogFragment"
    android:label="PlanItemDialogFragment">
</dialog>

3. 修改MenuFragment：导航并监听返回结果 #

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

    database = PlanListDatabase.getDatabase(requireActivity().applicationContext)

    binding.fab.setOnClickListener{
        // 导航到DialogFragment
        findNavController().navigate(R.id.planItemDialogFragment)
    }

    // 监听Dialog返回的数据
    findNavController().currentBackStackEntry?.savedStateHandle?.getLiveData<PlanItem>("newPlanItem")
        ?.observe(viewLifecycleOwner) { newItem ->
            // 处理返回的新数据，比如插入数据库、更新列表
            // 处理后移除数据，避免重复触发
            findNavController().currentBackStackEntry?.savedStateHandle?.remove<PlanItem>("newPlanItem")
        }
}

4. 修改PlanItemDialogFragment：返回数据 #

移除原有的监听器接口，修改确定按钮逻辑：

class PlanItemDialogFragment : DialogFragment() {
    private lateinit var binding: DialogNewItemBinding

    override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
        binding = DialogNewItemBinding.inflate(LayoutInflater.from(context))

        return AlertDialog.Builder(requireContext())
            .setTitle(hu.bme.aut.android.mobil_hf.R.string.new_plan_item)
            .setView(binding.root)
            .setPositiveButton(hu.bme.aut.android.mobil_hf.R.string.button_ok) { _, _ ->
                if (isValid()) {
                    val newItem = getPlanItem()
                    // 通过SavedStateHandle返回数据给上一个页面
                    findNavController().previousBackStackEntry?.savedStateHandle?.set("newPlanItem", newItem)
                    dismiss()
                }
            }
            .setNegativeButton(hu.bme.aut.android.mobil_hf.R.string.button_cancel) { _, _ ->
                dismiss()
            }
            .create()
    }
}

这样就完成了用Navigation参数实现数据返回的改造，无需依赖回调接口。

内容的提问来源于stack exchange，提问作者Naaaah