实用指南：kotlin - 2个Fragment实现左右显示，左边列表，右边详情，平板横、竖屏切换（一）

kotlin - 2个Fragment实现左右显示，左边列表，右边详情，平板横、竖屏切换

(要使用平板测试)平板横屏：左右fragment实现分屏效果，平板竖屏：只显示左边的fragment，点击才显示右边fragment
 屏幕旋转，会销毁重新创建，执行onCreate方法。
 在AndroidManifest.xml配置android:configChanges="screenSize|smallestScreenSize|screenLayout|orientation|keyboardHidden|navigation"属性,只调用onConfigurationChanged方法
 fragment的
add方法，
  如果新打开一个activity，该fragment只回调onStop()方法，没有调用onDestroy()方法。
  如果popBackStack或者finish，会回调onStop()和onDestroy()方法
 replace方法：旧的fragment执行onDestroy()方法，然后新建一个fragment，执行onViewCreated()方法。

package com.example.androidkotlindemo2.pad.leftright
import android.content.Intent
import android.content.res.Configuration
import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import com.example.androidkotlindemo2.R
import com.example.androidkotlindemo2.utils.LogUtils
/**
 * Author : wn
 * Email : maoning20080809@163.com
 * Date : 2025/8/30 21:41
 * Description : (要使用平板测试)平板横屏：左右fragment实现分屏效果，平板竖屏：只显示左边的fragment，点击才显示右边fragment
 * 屏幕旋转，会销毁重新创建，执行onCreate方法。
 * 在AndroidManifest.xml配置android:configChanges="screenSize|smallestScreenSize|screenLayout|orientation|keyboardHidden|navigation"属性,只调用onConfigurationChanged方法
 * fragment的
 * add方法，
 *  如果新打开一个activity，该fragment只回调onStop()方法，没有调用onDestroy()方法。
 *  如果popBackStack或者finish，会回调onStop()和onDestroy()方法
 * replace：旧的fragment执行onDestroy()方法，然后新建一个fragment，执行onViewCreated()方法。
 */
class LRFragmentActivity : AppCompatActivity() {
    //平板横屏
    private var isLandscape: Boolean = false
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.lr_fragment_main)
        LogUtils.d("LeftRightMainActivity onCreate");
        // 初始化显示列表Fragment
        if (savedInstanceState == null) {
            supportFragmentManager.beginTransaction()
                .replace(R.id.fragment_list_container, LRListFragment())
                .commit()
        }
        checkOrientation()
    }
    //检查横、竖屏
    private fun checkOrientation() {
        val orientation = resources.configuration.orientation
        isLandscape = orientation == Configuration.ORIENTATION_LANDSCAPE
    }
    fun setOnItemClick(position: Int, lrItem: LRItem) {
        if(position < 3){
            if(isLandscape){
                //平板横屏，左右显示fragment
                showItemDetailReplace(lrItem)
            } else {
                //平板竖屏，使用新的Activity显示
                startRightActivity(lrItem)
            }
        } else if(position < 6){
            //只适配平板横屏效果
            showItemDetailAdd(lrItem)
        } else {
            showItemNewActivity(lrItem)
        }
    }
    //竖屏打开新的Activity
    fun startRightActivity(lrItem: LRItem){
        val intent = Intent(this, LRRightActivity::class.java)
        intent.putExtra("lr_item", lrItem)
        startActivity(intent)
    }
    //使用replace方法
    fun showItemDetailReplace(lrItem: LRItem) {
        val detailFragment = LRDetailReplaceFragment.newInstance(lrItem)
        supportFragmentManager.beginTransaction()
            .replace(R.id.fragment_detail_container, detailFragment)
            .commit()
    }
    //使用add方法, 只回调onStop方法，不回调onDestroy方法
    fun showItemDetailAdd(LRItem: LRItem) {
        val detailNewFragment = LRDetailAddFragment.newInstance(LRItem)
        supportFragmentManager.beginTransaction()
            .add(R.id.fragment_detail_container, detailNewFragment)
            .addToBackStack("detail_new_fragment") // 添加这行才能popBackStack回退
            .commit()
    }
    //屏幕旋转，移除fragment
    fun removeDetailFragment(){
        val detailFragment = supportFragmentManager.findFragmentById(R.id.fragment_detail_container)
        if(detailFragment != null){
            supportFragmentManager.beginTransaction()
                .remove(detailFragment)
                .commit()
        }
    }
    //使用add方法, 只回调onStop方法，不回调onDestroy方法
    fun showItemNewActivity(LRItem: LRItem) {
        startActivity(Intent(this, LRNewActivity::class.java))
    }
    override fun onConfigurationChanged(newConfig: Configuration) {
        super.onConfigurationChanged(newConfig)
        LogUtils.i("LeftRightMainActivity onConfigurationChanged");
        checkOrientation()
        removeDetailFragment()
    }
    override fun onStop() {
        super.onStop()
        LogUtils.d("LeftRightMainActivity onDestroy")
    }
    override fun onDestroy() {
        super.onDestroy()
        LogUtils.d("LeftRightMainActivity onDestroy")
    }
    override fun onNewIntent(intent: Intent?) {
        super.onNewIntent(intent)
        LogUtils.i("LeftRightMainActivity onNewIntent")
    }
}

package com.example.androidkotlindemo2.pad.leftright
import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.fragment.app.Fragment
import androidx.recyclerview.widget.DividerItemDecoration
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
import com.example.androidkotlindemo2.R
import com.example.androidkotlindemo2.utils.LogUtils
/**
 * Author : wn
 * Email : maoning20080809@163.com
 * Date : 2025/8/30 21:41
 * Description :
 */
class LRListFragment : Fragment(){
    private lateinit var recyclerView: RecyclerView
    private lateinit var adapter: LRAdapter
    private var LRItemList = mutableListOf()
    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        return inflater.inflate(R.layout.lr_fragment_item_list, container, false)
    }
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        setupRecyclerView(view)
        loadItems()
    }
    private fun setupRecyclerView(view: View) {
        recyclerView = view.findViewById(R.id.recycler_view)
        adapter = LRAdapter(LRItemList, object : LROnItemClickInter{
            override fun setOnItemClick(position: Int, lrItem: LRItem) {
                // 通知Activity显示详情
                (activity as? LRFragmentActivity)?.setOnItemClick(position,lrItem)
            }
            override fun setOnLongClickListener(position: Int, lrItem: LRItem) {
                LogUtils.i("长按：${position}")
            }
        })
        recyclerView.layoutManager = LinearLayoutManager(requireContext())
        recyclerView.adapter = adapter
        recyclerView.addItemDecoration(
            DividerItemDecoration(requireContext(), LinearLayoutManager.VERTICAL)
        )
    }
    private fun loadItems() {
        for(i in 1 .. 20){
            LRItemList.add(LRItem(i, "项目${i}", "这是第${i}个项目的详细描述"))
        }
        adapter.notifyDataSetChanged()
    }
}

package com.example.androidkotlindemo2.pad.leftright
import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.Button
import android.widget.TextView
import androidx.core.content.ContextCompat
import androidx.fragment.app.Fragment
import com.example.androidkotlindemo2.MyApp
import com.example.androidkotlindemo2.R
import com.example.androidkotlindemo2.utils.LogUtils
/**
 * Author : wn
 * Email : maoning20080809@163.com
 * Date : 2025/8/30 21:45
 * Description : 新的详情，使用fragment的add方法调用，只会调用onStop()
 */
class LRDetailAddFragment : Fragment() {
    companion object {
        private const val ARG_ITEM = "item"
        fun newInstance(LRItem: LRItem): LRDetailAddFragment {
            val fragment = LRDetailAddFragment()
            val args = Bundle().apply {
                putParcelable(ARG_ITEM, LRItem)
            }
            fragment.arguments = args
            return fragment
        }
    }
    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        return inflater.inflate(R.layout.lr_fragment_item_detail, container, false)
    }
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        LogUtils.w("LRDetailAddFragment onViewCreated ----------------------------")
        LogUtils.w("LRDetailAddFragment onViewCreated()  ${this}")
        arguments?.getParcelable(ARG_ITEM)?.let { item ->
            displayItemDetails(view, item)
        }
        view.findViewById(R.id.lr_item_details_back).visibility = View.VISIBLE
        //返回
        view.findViewById(R.id.lr_item_details_back).setOnClickListener {
            LogUtils.i("LRDetailNewFragment返回")
            requireActivity().supportFragmentManager.popBackStack()
        }
        view.findViewById(R.id.lr_item_details_finish).visibility = View.VISIBLE
        //关闭 -
        view.findViewById(R.id.lr_item_details_finish).setOnClickListener {
            LogUtils.i("LRDetailNewFragment关闭")
            requireActivity().finish()
        }
    }
    override fun onStart() {
        super.onStart()
        LogUtils.w("LRDetailAddFragment onStart() ${this}")
    }
    override fun onResume() {
        super.onResume()
        LogUtils.w("LRDetailAddFragment onResume() ${this}")
    }
    override fun onPause() {
        super.onPause()
        LogUtils.w("LRDetailAddFragment onPause() ${this}")
    }
    override fun onStop() {
        super.onStop()
        LogUtils.w("LRDetailAddFragment onStop() ${this}")
    }
    override fun onDestroy() {
        super.onDestroy()
        LogUtils.w("LRDetailAddFragment onDestroy()  ${this}")
    }
    private fun displayItemDetails(view: View, LRItem: LRItem) {
        view.findViewById(R.id.title_text_view).text = LRItem.title
        view.findViewById(R.id.description_text_view).text = "新页面：" + LRItem.description
        view.findViewById(R.id.description_text_view).setTextColor(ContextCompat.getColor(MyApp.myApp,R.color.blue))
        view.findViewById(R.id.description_text_view).setTextSize(30f)
    }
}

package com.example.androidkotlindemo2.pad.leftright
import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.Button
import android.widget.TextView
import androidx.fragment.app.Fragment
import com.example.androidkotlindemo2.R
import com.example.androidkotlindemo2.utils.LogUtils
/**
 * Author : wn
 * Email : maoning20080809@163.com
 * Date : 2025/8/30 21:45
 * Description : 使用replace方法，会调用onStop()和onDestroy()方法，
 */
class LRDetailReplaceFragment : Fragment() {
    companion object {
        private const val ARG_ITEM = "item"
        fun newInstance(LRItem: LRItem): LRDetailReplaceFragment {
            val fragment = LRDetailReplaceFragment()
            val args = Bundle().apply {
                putParcelable(ARG_ITEM, LRItem)
            }
            fragment.arguments = args
            return fragment
        }
    }
    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        return inflater.inflate(R.layout.lr_fragment_item_detail, container, false)
    }
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        LogUtils.i("LRDetailReplaceFragment onViewCreated ----------------------------")
        LogUtils.d("LRDetailReplaceFragment onViewCreated()  ${this}")
        arguments?.getParcelable(ARG_ITEM)?.let { item ->
            displayItemDetails(view, item)
        }
        //返回
        view.findViewById(R.id.lr_item_details_back).visibility = View.GONE
        view.findViewById(R.id.lr_item_details_finish).visibility = View.GONE
    }
    override fun onStart() {
        super.onStart()
        LogUtils.d("LRDetailReplaceFragment onStart()  ${this}")
    }
    override fun onResume() {
        super.onResume()
        LogUtils.d("LRDetailReplaceFragment onResume()  ${this}")
    }
    override fun onPause() {
        super.onPause()
        LogUtils.d("LRDetailReplaceFragment onPause()  ${this}")
    }
    override fun onStop() {
        super.onStop()
        LogUtils.d("LRDetailReplaceFragment onStop()  ${this}")
    }
    override fun onDestroy() {
        super.onDestroy()
        LogUtils.d("LRDetailReplaceFragment onDestroy()  ${this}")
    }
    private fun displayItemDetails(view: View, LRItem: LRItem) {
        view.findViewById(R.id.title_text_view).text = LRItem.title
        view.findViewById(R.id.description_text_view).text = LRItem.description
    }
}

package com.example.androidkotlindemo2.pad.leftright
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.LinearLayout
import android.widget.TextView
import androidx.cardview.widget.CardView
import androidx.core.content.ContextCompat
import androidx.recyclerview.widget.RecyclerView
import com.example.androidkotlindemo2.MyApp
import com.example.androidkotlindemo2.R
/**
 * Author : wn
 * Email : maoning20080809@163.com
 * Date : 2025/8/30 21:42
 * Description :
 */
class LRAdapter(
    private val itemList: List,
    private val listener: LROnItemClickInter
) : RecyclerView.Adapter() {
    var selectedPosition = -1
    inner class ItemViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        val titleTextView: TextView = itemView.findViewById(R.id.title_text_view)
        val container: LinearLayout = itemView.findViewById(R.id.item_container)
    }
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ItemViewHolder {
        val view = LayoutInflater.from(parent.context)
            .inflate(R.layout.lr_fragment_item, parent, false)
        return ItemViewHolder(view)
    }
    override fun onBindViewHolder(holder: ItemViewHolder, position: Int) {
        val lrItem = itemList[position]
        holder.titleTextView.text = lrItem.title
        holder.container.setOnClickListener {
            listener.setOnItemClick(position, lrItem)
            selectedPosition = position
            notifyDataSetChanged()
        }
        holder.container.setOnLongClickListener {
            listener.setOnLongClickListener(position, lrItem)
            true
        }
        if(selectedPosition == position){
            holder.container.setBackgroundColor(ContextCompat.getColor(MyApp.myApp, R.color.lr_item_selected_bg))
        } else {
            holder.container.setBackgroundColor(ContextCompat.getColor(MyApp.myApp, R.color.lr_item_default_bg))
        }
    }
    override fun getItemCount(): Int = itemList.size
}

package com.example.androidkotlindemo2.pad.leftright
import android.os.Bundle
import android.widget.Button
import androidx.appcompat.app.AppCompatActivity
import com.example.androidkotlindemo2.R
import com.example.androidkotlindemo2.utils.LogUtils
/**
 * Author : wn
 * Email : maoning20080809@163.com
 * Date : 2025/9/6 13:04
 * Description : 打开新的页面
 */
class LRNewActivity : AppCompatActivity(){
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.lr_activity_new)
        LogUtils.e("LRNewActivity onViewCreated ----------------------------")
        findViewById(R.id.lr_activity_new_close).setOnClickListener {
            finish()
        }
    }
    override fun onCreateDescription(): CharSequence? {
        return super.onCreateDescription()
    }
    override fun onDestroy() {
        super.onDestroy()
        LogUtils.e("LRNewActivity onDestroy ----------------------------")
    }
}

package com.example.androidkotlindemo2.pad.leftright
/**
 * Author : wn
 * Email : maoning20080809@163.com
 * Date : 2025/9/6 9:46
 * Description :
 */
interface LROnItemClickInter {
    //点击
    fun setOnItemClick(position: Int, lrItem: LRItem)
    //长按
    fun setOnLongClickListener(position: Int, lrItem: LRItem)
}

package com.example.androidkotlindemo2.pad.leftright
import android.os.Bundle
import android.widget.Button
import androidx.appcompat.app.AppCompatActivity
import com.example.androidkotlindemo2.R
import com.example.androidkotlindemo2.utils.LogUtils
/**
 * Author : wn
 * Email : maoning20080809@163.com
 * Date : 2025/9/6 13:04
 * Description : 在Activity中显示右边的fragment
 */
class LRRightActivity : AppCompatActivity(){
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.lr_activity_right)
        val lrItem = intent.getParcelableExtra("lr_item") as LRItem
        if (savedInstanceState == null) {
            supportFragmentManager.beginTransaction()
                .replace(R.id.fragment_right_container, LRDetailReplaceFragment.newInstance(lrItem))
                .commit()
        }
    }
}

package com.example.androidkotlindemo2.pad.leftright
import android.os.Parcel
import android.os.Parcelable
/**
 * Author : wn
 * Email : maoning20080809@163.com
 * Date : 2025/8/30 21:41
 * Description :
 */
data class LRItem(
    val id: Int,
    val title: String,
    val description: String,
    val imageUrl: String? = null
) : Parcelable {
    constructor(parcel: Parcel) : this(
        parcel.readInt(),
        parcel.readString() ?: "",
        parcel.readString() ?: "",
        parcel.readString()
    )
    override fun writeToParcel(parcel: Parcel, flags: Int) {
        parcel.writeInt(id)
        parcel.writeString(title)
        parcel.writeString(description)
        parcel.writeString(imageUrl)
    }
    override fun describeContents(): Int {
        return 0
    }
    companion object CREATOR : Parcelable.Creator {
        override fun createFromParcel(parcel: Parcel): LRItem {
            return LRItem(parcel)
        }
        override fun newArray(size: Int): Array {
            return arrayOfNulls(size)
        }
    }
}

lr_fragment_main.xml布局

lr_fragment_item_list.xml布局

lr_fragment_item_detail.xml布局

lr_fragment_item.xml布局

lr_activity_new.xml布局

lr_activity_right.xml布局

drawable：

lr_click_item_bg.xml

#FFFFFF
#FF00FF