Android自定义view实现列表内左滑删除Item

import Android.annotation.SuppressLint
import android.content.Context
import android.graphics.Color
import android.os.Build
import android.util.AttributeSet
import android.util.TypedValue
import android.view.Gravity
import android.view.MotionEvent
import android.view.View
import android.widget.Scroller
import android.widget.TextView
import androidx.annotation.Requiresapi
import androidx.constraintlayout.widget.ConstraintLayout
import Kotlin.math.abs

class LeftDeleteItemLayout : ConstraintLayout {
    private val mDeleteView: View?
    var mDeleteClickListener: OnClickListener? = null
    //流畅滑动
    private var mScroller = Scroller(context)
    //上次事件的横坐标
    private var mLastX = -1f
    //控制控件结束的runnable
    private val stopMoveRunnable: Runnable = Runnable { stopMove() }
    constructor(context: Context) : this(context, null, 0)
    constructor(context: Context, attrs: AttributeSet?) : this(context, attrs, 0)
    constructor(context: Context, attrs: AttributeSet?, defStyleAttr: Int) :
            super(context, attrs, defStyleAttr)
    @RequiresApi(Build.VERSION_CODES.LOLLIPOP)
    constructor(context: Context, attrs: AttributeSet?, defStyleAttr: Int, defStyleRes: Int) :
            super(context, attrs, defStyleAttr, defStyleRes)
    init {
        //kotlin的初始化函数
        mDeleteView = makeDeleteView(context)
        addView(mDeleteView)
    }
    //创建删除框，设置好位置对齐自身最右边
    private fun makeDeleteView(context: Context): View {
        val deleteView = TextView(context)
        //给当前控件一个id，用于删除控件约束
        this.id = generateViewId()
        //设置布局参数
        deleteView.layoutParams = LayoutParams(
            dp2px(context, 100f), 0
        ).apply {
            //设置约束条件
            leftToRight = id
            topToTop = id
            bottomToBottom = id
        }
        //设置其他参数
        deleteView.text = "删除"
        deleteView.gravity = Gravity.CENTER
        deleteView.setTextColor(Color.WHITE)
        deleteView.textSize = sp2px(context,18f).toFloat()
        deleteView.setBackgroundColor(Color.RED)
        //设置点击回调
        deleteView.setOnClickListener(mDeleteClickListener)
        return deleteView
    }
    //拦截事件
    override fun onInterceptTouchEvent(event: MotionEvent?): Boolean {
        event?.let {
            when(event.action) {
                //down事件记录x，不拦截，当move的时候才会用到
                MotionEvent.ACTION_DOWN -> mLastX = event.x
                //拦截本控件内的移动事件
                MotionEvent.ACTION_MOVE -> return true
            }
        }
        return super.onInterceptTouchEvent(event)
    }
    //处理事件
    @SuppressLint("ClickableViewAccessibility")
    override fun onTouchEvent(event: MotionEvent?): Boolean {
        event?.let {
            when(event.action) {
                MotionEvent.ACTION_MOVE -> moveItem(event)
                MotionEvent.ACTION_UP -> stopMove()
            }
        }
        return super.onTouchEvent(event)
    }
    private fun moveItem(e: MotionEvent) {
        //Log.e("TAG", "moveItem: mLastX=$mLastX")
        //如果没有收到down事件，不应该移动
        if (mLastX == -1f) return
        val dx = mLastX - e.x
        //更新点击的横坐标
        mLastX = e.x
        //检查mItem移动后应该在[-deleteLength, 0]内
        val deleteWidth = mDeleteView!!.width
        if ((scrollX + dx) <= deleteWidth && (scrollX + dx) >= 0) {
            //触发移动
            scrollBy(dx.toInt(), 0)
        }
        //如果一段时间没有移动时间，mLastX还没被stopMove重置为-1，那就是移动到其他地方了
        //设置200毫秒没有新事件就触发stopMove
        removeCallbacks(stopMoveRunnable)
        postDelayed(stopMoveRunnable, 200)
    }
    private fun stopMove() {
        //如果移动过半了，应该判定左滑成功
        val deleteWidth = mDeleteView!!.width
        if (abs(scrollX) >= deleteWidth / 2f) {
            //触发移动至完全展开
            mScroller.startScroll(scrollX, 0, deleteWidth - scrollX, 0)
        }else {
            //如果移动没过半应该恢复状态，则恢复到原来状态
            mScroller.startScroll(scrollX, 0, - scrollX, 0)
        }
        invalidate()
        //清除状态
        mLastX = -1f
    }
    //流畅地滑动
    override fun computeScroll() {
        if (mScroller.computeScrollOffset()) {
            scrollTo(mScroller.currX, mScroller.currY)
            postInvalidate()
        }
    }
    //单位转换
    @Suppress("SameParameterValue")
    private fun dp2px(context: Context, dpVal: Float): Int {
        return TypedValue.applyDimension(
            TypedValue.COMPLEX_UNIT_DIP, dpVal, context.resources
                .displayMetrics
        ).toInt()
    }
    @Suppress("SameParameterValue")
    private fun sp2px(context: Context, spVal: Float): Int {
        val fontScale = context.resources.displayMetrics.scaledDensity
        return (spVal * fontScale + 0.5f).toInt()
    }

    //处理事件
    @SuppressLint("ClickableViewAccessibility")
    override fun onTouchEvent(event: MotionEvent): Boolean {
        when(event.action) {
            MotionEvent.ACTION_DOWN -> return true
            MotionEvent.ACTION_MOVE -> moveItem(event)
            MotionEvent.ACTION_UP -> stopMove()
        }
        return super.onTouchEvent(event)
    }