RecycleView和Adapter的基本使用

1.創建佈局文件，word_fragment用來放Recycle，word_fragment_grad_cell用來放小單元

word_fragment佈局：

word_fragment_grad_cell佈局：（卡片佈局）

2.創建適配器wordFragmentAdapter類

package com.example.ngsl.wordFragment

import android.content.Intent
import android.net.Uri
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.recyclerview.widget.DiffUtil
import androidx.recyclerview.widget.ListAdapter
import androidx.recyclerview.widget.RecyclerView
import com.example.ngsl.R
import com.example.ngsl.room.Word
import kotlinx.android.synthetic.main.word_fragment_grad_cell.view.*

//適配器：告訴view有哪些內容，並且如何填充view
class WordFragmentAdapter : ListAdapter<Word, MyViewHolder>(DiffCallBack) {
    //比較器，比較每一行的對象
    object DiffCallBack : DiffUtil.ItemCallback<Word>() {
        override fun areItemsTheSame(oldItem: Word, newItem: Word): Boolean {
            //比較是不是同一個對象
            return oldItem.wordId == newItem.wordId
        }
        override fun areContentsTheSame(oldItem: Word, newItem: Word): Boolean {
            //比較內容是否相同
            return oldItem == newItem
        }
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyViewHolder {
        //加載view，就是每一個小單元word_fragment_grad_cell
        val view = LayoutInflater.from(parent.context).inflate(R.layout.word_fragment_grad_cell, parent, false)
        val holder = MyViewHolder(view)
        holder.itemView.apply {
            //將監聽事件放在這，就不會每次加載一個item時新創建監聽事件
            val onClickListener = View.OnClickListener {
                val uri = Uri.parse("https://m.youdao.com/dict?le=eng&q=${this.textViewEnglish.text}")
                Intent(Intent.ACTION_VIEW).apply {
                    this.data = uri
                    holder.itemView.context.startActivity(this)
                }
            }
            this.textViewEnglish.setOnClickListener(onClickListener)
            this.imageView.setOnClickListener(onClickListener)
        }
        return holder
    }

    override fun onBindViewHolder(holder: MyViewHolder, position: Int) {
        //加載資源
        holder.itemView.apply {
            val item = getItem(position)
            this.textViewWordId.text = item.wordId.toString()
            this.textViewEnglish.text = item.english
        }
    }
}

//這個很重要
class MyViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView)

3.在wordFragment中加載適配器

fragment最好在onActivityCreated中操作

package com.example.ngsl.wordFragment

import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.fragment.app.Fragment
import androidx.lifecycle.Observer
import androidx.lifecycle.ViewModelProvider
import androidx.recyclerview.widget.GridLayoutManager
import com.example.ngsl.R
import kotlinx.android.synthetic.main.word_fragment.*

class WordFragment : Fragment() {

	//ViewModel 管理數據的
    private lateinit var viewModel: WordViewModel

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

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)

        //創建適配器
        val wordFragmentAdapter = WordFragmentAdapter()
        recycleView.apply {
            adapter = wordFragmentAdapter
            //頁面佈局，1列
            layoutManager = GridLayoutManager(requireContext(), 1)
        }

        //ViewModel
        viewModel = ViewModelProvider(this).get(WordViewModel::class.java)
        viewModel.allWord.observe(viewLifecycleOwner, Observer {
            //爲適配器提供數據
            wordFragmentAdapter.submitList(it)
        })
        
		//這是一個小功能，可以拖動列表的item
//        ItemTouchHelper(object : ItemTouchHelper.SimpleCallback(0, ItemTouchHelper.START) {
//            override fun onMove(
//                recyclerView: RecyclerView,
//                viewHolder: RecyclerView.ViewHolder,
//                target: RecyclerView.ViewHolder
//            ): Boolean {
//                return false
//            }
//
//            override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {
//                //滑動之後要做的事
//                val itemPosition = viewHolder.adapterPosition //獲取被刪除對象的位置
//                //更新列表數據
//            }
//        }).attachToRecyclerView(recycleView)
    }
}

4.GitHub源碼鏈接

整個項目有很多組件，只看你需要的部分：https://github.com/YDDUONG/NGSL-English
如果覺得有用，點個贊吧