Android/Kotlin 如何实现DialogFragment向Fragment传递数据

针对你的需求，这里提供两种可直接落地的实现方式，均基于你现有代码修改：

方案1：接口回调实现（适合简单传值场景，逻辑直观） #

步骤1：修改TimePickerFragment.kt，定义回调接口 #

package com.example.mytablayout.fragments

import android.app.Dialog
import android.app.TimePickerDialog
import android.content.Context
import android.os.Bundle
import android.text.format.DateFormat
import android.widget.TimePicker
import androidx.fragment.app.DialogFragment
import java.util.*

class TimePickerFragment: DialogFragment(), TimePickerDialog.OnTimeSetListener {
    // 定义时间选择回调接口
    interface OnTimeSelectedListener {
        fun onTimeSelected(hour: Int, minute: Int)
    }

    private lateinit var listener: OnTimeSelectedListener

    // Fragment绑定上下文时获取父Fragment的回调实例
    override fun onAttach(context: Context) {
        super.onAttach(context)
        // 你是通过Weight的childFragmentManager启动弹窗，所以parentFragment就是Weight实例
        listener = parentFragment as OnTimeSelectedListener
    }

    override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
        val c = Calendar.getInstance()
        val hour = c.get(Calendar.HOUR_OF_DAY) // 这里建议用HOUR_OF_DAY避免12小时制问题
        val minute = c.get(Calendar.MINUTE)
        return TimePickerDialog(requireActivity(), this, hour, minute, DateFormat.is24HourFormat(activity))
    }

    override fun onTimeSet(view: TimePicker, hour: Int, minute: Int) {
        // 选中时间后触发回调，把值传给父Fragment
        listener.onTimeSelected(hour, minute)
    }
}

步骤2：修改Weight.kt，实现回调接口更新按钮 #

注意：你原代码中把btnTime声明为全局变量会有内存泄漏风险，建议移到类内部作为私有成员

package com.example.mytablayout

import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.Button
import androidx.fragment.app.Fragment
import com.example.mytablayout.fragments.TimePickerFragment
import java.util.*

class Weight : Fragment(), TimePickerFragment.OnTimeSelectedListener {
    // 把按钮声明移到类内部
    private lateinit var btnTime: Button

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        return inflater.inflate(R.layout.fragment_weight, container, false)
    }

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

        val c = Calendar.getInstance()
        val hour = c.get(Calendar.HOUR_OF_DAY)
        val minute = c.get(Calendar.MINUTE)

        btnTime = view.findViewById(R.id.btnTime)
        btnTime.text = String.format("%02d:%02d", hour, minute)

        btnTime.setOnClickListener {
            val newTimeFragment = TimePickerFragment()
            newTimeFragment.show(childFragmentManager, "timePicker")
        }
    }

    // 实现回调接口，接收选中的时间更新按钮
    override fun onTimeSelected(hour: Int, minute: Int) {
        btnTime.text = String.format("%02d:%02d", hour, minute)
    }
}

方案2：ViewModel实现（适合复杂场景，配置变更不丢失数据） #

如果你的项目后续有更复杂的数据共享需求，推荐用ViewModel实现，无需写回调接口。

步骤1：新建共享ViewModel类TimeViewModel.kt #

package com.example.mytablayout

import androidx.lifecycle.LiveData
import androidx.lifecycle.MutableLiveData
import androidx.lifecycle.ViewModel

class TimeViewModel : ViewModel() {
    private val _selectedTime = MutableLiveData<String>()
    val selectedTime: LiveData<String> = _selectedTime

    fun updateTime(hour: Int, minute: Int) {
        _selectedTime.value = String.format("%02d:%02d", hour, minute)
    }
}

步骤2：修改TimePickerFragment.kt，选中时间后更新ViewModel #

override fun onTimeSet(view: TimePicker, hour: Int, minute: Int) {
    // 获取和父Fragment共享的ViewModel实例
    val timeViewModel = ViewModelProvider(requireParentFragment())[TimeViewModel::class.java]
    timeViewModel.updateTime(hour, minute)
}

步骤3：修改Weight.kt，观察ViewModel数据更新按钮 #

class Weight : Fragment() {
    private lateinit var btnTime: Button
    // 初始化当前Fragment作用域的ViewModel
    private val timeViewModel: TimeViewModel by viewModels()

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        // ...原有初始化代码不变

        // 观察时间变化自动更新按钮
        timeViewModel.selectedTime.observe(viewLifecycleOwner) { timeStr ->
            btnTime.text = timeStr
        }

        btnTime.setOnClickListener {
            val newTimeFragment = TimePickerFragment()
            newTimeFragment.show(childFragmentManager, "timePicker")
        }
    }
}

内容的提问来源于stack exchange，提问作者MZX