Android RecyclerView canScrollVertically方向与返回值，Kotlin

 

import android.os.Bundle
import android.util.Log
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity
import androidx.core.content.ContextCompat
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView


class MainActivity : AppCompatActivity() {
    companion object {
        const val TAG = "fly"
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val rv = findViewById<RecyclerView>(R.id.rv)
        val linearLayoutManager = LinearLayoutManager(this)
        linearLayoutManager.orientation = LinearLayoutManager.VERTICAL
        rv.layoutManager = linearLayoutManager
        val adapter = MyAdapter()
        rv.adapter = adapter

        rv.addOnScrollListener(object : RecyclerView.OnScrollListener() {
            override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
                super.onScrolled(recyclerView, dx, dy)

                val b1 = recyclerView.canScrollVertically(1)
                Log.d(TAG, "scrolling up $b1")

                val b2 = recyclerView.canScrollVertically(-1)
                Log.d(TAG, "scrolling down $b2")
            }
        })
    }

    class MyAdapter : RecyclerView.Adapter<MyVH> {
        constructor() {

        }

        override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyVH {
            val v = LayoutInflater.from(parent.context).inflate(android.R.layout.simple_list_item_1, parent, false)
            return MyVH(v)
        }

        override fun getItemCount(): Int {
            return 30
        }

        override fun onBindViewHolder(holder: MyVH, position: Int) {
            holder.text?.text = "$position"
        }
    }

    class MyVH : RecyclerView.ViewHolder {
        var text: TextView? = null

        constructor(itemView: View) : super(itemView) {
            text = itemView.findViewById(android.R.id.text1)
            text?.setTextColor(ContextCompat.getColor(itemView.context, android.R.color.holo_red_light))
        }
    }
}

 

 

1、当手指在屏幕下滑，直到把RecyclerView第一个item（0）显示在最顶部，即RecyclerView不能往下再滑的时候：
scrolling up   true
scrolling down false

 

 

2、当手指在屏幕上滑，直到把RecyclerView最后一个item（29）显示在最底部，即RecyclerView不能往上再滑的时候：
scrolling up   false
scrolling down true

 

除此以外，当RecyclerView处于既可以上滑也可以下滑时候，canScrollVertically返回值均为true：
scrolling up   true
scrolling down true
 

 

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