当数据在 Kotlin 中发生更改时，如何在回收器视图中重新绑定项目？

Question

我自定义了一个回收视图类，它将显示 val 备份的内容项目列表： 列表

现在我在RecyclerView类之外修改backupItemList的数据，我认为代码D将在UI中显示最新的数据，但我失败了，UI仍然显示旧数据。我必须使用代码C来显示最新数据。

代码D有什么问题？

代码 A

class UIMain : AppCompatActivity() {
   override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.layout_main)                       

        allList= SettingHandler().getListAllSetting()            

        mRecyclerView.layoutManager = LinearLayoutManager(this, LinearLayout.VERTICAL, false)
        mCustomAdapter= CustomAdapter(allList)
        mRecyclerView.adapter= mCustomAdapter


   }


   public override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent) {
       //Code C          
       if (resultCode == RESULT_OK) {
           allList=SettingHandler().getListAllSetting()
           mCustomAdapter= CustomAdapter(allList)
           mRecyclerView.adapter= mCustomAdapter
           mCustomAdapter.notifyDataSetChanged()
           mCustomAdapter.setSelectedItem(selectedBackupItem)  
       }


       //Code D     
       if (resultCode == RESULT_OK) {
          allList=SettingHandler().getListAllSetting()                
          mCustomAdapter.setSelectedItem(selectedBackupItem)                
       }         

   }        

}

代码B

  class CustomAdapter (val backupItemList: List<MSetting>) : RecyclerView.Adapter<CustomAdapter.ViewHolder>() {

        val noRecord=-1
        private var mSelectedItem = noRecord

        override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CustomAdapter.ViewHolder {
            val v = LayoutInflater.from(parent.context).inflate(R.layout.item_recyclerview, parent, false)
            return ViewHolder(v)
        }

        fun getSelectedItem():Int{
            return  mSelectedItem
        }

        fun setSelectedItem(index:Int){
            if (index in 0..(backupItemList.size-1) ){
                mSelectedItem=index
                notifyDataSetChanged();
            }

        }

        override fun onBindViewHolder(holder: CustomAdapter.ViewHolder, position: Int) {
            holder.bindItems(backupItemList[position])
        }

        override fun getItemCount(): Int {
            return backupItemList.size
        }

        inner class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {

            fun bindItems(aMSetting: MSetting) {
                itemView.tvSubject.text=aMSetting.name
                itemView.tvCreatedDate.text=aMSetting.createdDate.toDateString()
                itemView.tvDescription.text=aMSetting.description   
                itemView.radioButton.setOnClickListener {
                mSelectedItem=adapterPosition
                notifyDataSetChanged();
            }

            if(adapterPosition == 0 && mSelectedItem == noRecord) {             
                itemView.radioButton.isChecked = true
                mSelectedItem=adapterPosition
            }
            else {
                itemView.radioButton.isChecked =(adapterPosition == mSelectedItem)
            }       
            }

        }

    }

致公民利利斯特：

如果我使用代码E（我用var替换val），代码C和代码D都会得到相同的结果，为什么？

代码E

  class CustomAdapter (var backupItemList: List<MSetting>) : RecyclerView.Adapter<CustomAdapter.ViewHolder>() {

        val noRecord=-1
        private var mSelectedItem = noRecord

        override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CustomAdapter.ViewHolder {
            val v = LayoutInflater.from(parent.context).inflate(R.layout.item_recyclerview, parent, false)
            return ViewHolder(v)
        }

        fun getSelectedItem():Int{
            return  mSelectedItem
        }

        fun setSelectedItem(index:Int){
            if (index in 0..(backupItemList.size-1) ){
                mSelectedItem=index
                notifyDataSetChanged();
            }

        }

        override fun onBindViewHolder(holder: CustomAdapter.ViewHolder, position: Int) {
            holder.bindItems(backupItemList[position])
        }

        override fun getItemCount(): Int {
            return backupItemList.size
        }

        inner class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {

            fun bindItems(aMSetting: MSetting) {
                itemView.tvSubject.text=aMSetting.name
                itemView.tvCreatedDate.text=aMSetting.createdDate.toDateString()
                itemView.tvDescription.text=aMSetting.description   
                itemView.radioButton.setOnClickListener {
                mSelectedItem=adapterPosition
                notifyDataSetChanged();
            }

            if(adapterPosition == 0 && mSelectedItem == noRecord) {             
                itemView.radioButton.isChecked = true
                mSelectedItem=adapterPosition
            }
            else {
                itemView.radioButton.isChecked =(adapterPosition == mSelectedItem)
            }       
            }

        }

    }




Answer 1

在代码D中，您正在覆盖allList的引用。

CustomAdapter中的backupItemList具有相同的引用。因此，如果重新分配allList的引用，则不会在recycler视图中拾取更改

首先确保allList是可变的

val allList = mutableListOf<MSetting>()

然后是代码D

allList.clear()
allList.addAll(SettingHandler().getListAllSetting())
mCustomAdapter.notifyDataSetChanged()

Answer 2

在您的Active onCreate方法中

    override fun onCreate(savedInstanceState: Bundle?) {
            super.onCreate(savedInstanceState)
            setContentView(R.layout.layout_main)                
    
            allList = ArrayList< MSetting>()
            mCustomAdapter = CustomAdapter(mChildList)
            mRecyclerView.layoutManager = LinearLayoutManager(context)
            mRecyclerView.adapter = mCustomAdapter
    }

现在在 活动结果

     public override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent) {

           //Code C          
           if (resultCode == RESULT_OK) {
              if(data != null){
                 allList.clear()
                 allList.addAll(SettingHandler().getListAllSetting())
                 mCustomAdapter.notifyDataSetChanged()
                 mCustomAdapter.setSelectedItem(selectedBackupItem) 
              } 
           }
        
      }        

Answer 3

秘密也许就藏在这里:

类custom adapter(val backup itemlist:List)

当您初始化CustomAdapter的实例时，该值将复制到属性backupItemList，而不是分配引用。因此，当您更改UIMain的属性allList时，backupItemList不会像您预期的那样更改。

正如Ganesh Tikone所写，解决方案很简单：添加一个方法来更新backupItemList。

fun updateData(data: List<MovieModel>) {
    backupItemList.clear()
    backupItemList.addAll(data)
    notifyDataSetChanged()
}

并将代码D更改为：

//Code D     
   if (resultCode == RESULT_OK) {
      allList=SettingHandler().getListAllSetting()  
      mCustomAdapter.updateData(allList)    
      mCustomAdapter.setSelectedItem(selectedBackupItem)                
   }  

试一试。