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
/**
 * 左划删除控件
 * 能在控件实现左滑吗？如何传入自定义的布局？
 * 思路：
 * 1、一个容器，左右两部分，左边外部导入，右边删除框 x 增加层级
 * 2、在 View 右边追加一个删除款 x 需要在 View 内拦截事件
 * 3、在 ConstraintLayout 内部添加一个删除框，左边对其 parent 右边
 *
 * @author silence
 * @date 2022-09-27
 */
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)
    }