Day 11 | 进阶清单元件RecyclerView

RecyclerView

RecyclerView是进阶版的清单元件，它取代了基本的ListView与GridView，不只是因为RecyclerView拥有多元的呈现样貌，而是它强制开发者实作ViewHolder类别，以实现画面复用的机制。

指派给RecyclerView的Adapter必须继承自RecyclerView.Adapter类别，以下说明如何使用RecyclerView

1. 客制化Adapter与ViewHolder，MyAdapter须继承RecyclerView.Adapter类别，并建立ViewHolder继承自 RecyclerView.ViewHolder类别。

   class MyAdapter(private val data: ArrayList<Item>, private val layout: Int):
   RecyclerView.Adapter<MyAdapter.ViewHolder>() {
   //实作RecyclerView.ViewHolder来储存View
   class ViewHolder(V: View): RecyclerView.ViewHolder(V){
   	val img_photo = v.findViewById<ImageVlew>(R.id.img_photo)
   	val tv_msg = v.findViewById<TextView>(R.id.tv_msg)
   }
   //回传资料数量
   override fun getItemcount() = data.size
   //建立ViewHolder与Layout并连彼此
   override fun onCreateViewHolder(viewGroup: ViewGroup, position: Int) :
   ViewHolder {
   	val v= LayoutInflater.from(viewGroup.context).inflate(layout, viewGroup, false)
   	return ViewHolder (v)
   }
   //将资科指派给元件呈现
   override fun onBindViewHolder (holder: ViewHolder, position: Int) {
   	holder.img_photo.setImageResource (data[position].photo)
   	holder.tv_msg.text = data[position].name
   }
   

2. 设定排列方式与方向。RecyclerView的排列方式由LayoutManager决定，最常见的是使用LinearLayoutManager与GridLayoutManager实现ListView与GridView的效果，并用LayoutManager的orientation属性决定方向。

   //建立LipearLayoutManager物件
   val linearLayoutManager = LinearLayoutManager (this)
   //设定清单的排列方向
   linearLayoutManager.orientation = LinearLayoutManager.VERTICAL
   //连结LinearLayoutManager
   recyclerView.layoutManager = linearLayoutManager
   //连结adapter
   recyclerView.adapter = MyAdapter(item, R.layout,adapter_horizontal)
   //建立GridLayoutManager物件·并设定每栏的数量
   val gridLayoutManager = GridLayoutManager(this, 3)
   //设定清单的排列方向
   gridLayoutManager.orientation = GridLayoutManager.VERTICAL
   //连结GridLayoutManager
   recyclerView.layoutManager  = gridLayoutManaget
   //连结adapter
   recyclerView.adapter = MyAdapter(item, R.layout,adapter_vertical)