模仿微信涂抹文字选择。

gistfile1.txt

package top.ntutn.swipeselectview

import android.annotation.SuppressLint
import android.content.Context
import android.graphics.Rect
import android.util.AttributeSet
import android.view.MotionEvent
import android.view.View
import androidx.core.view.children
import com.google.android.material.chip.ChipGroup
import kotlin.math.abs
import kotlin.math.max
import kotlin.math.min
import kotlin.math.roundToInt
import kotlin.math.sqrt

class SwipeSelectLayout @JvmOverloads constructor(context: Context, defStyleAttr: AttributeSet? = null, defStyleRes: Int = 0) : ChipGroup(context, defStyleAttr, defStyleRes) {
    private val childrenSelectionOnMoveStart = mutableMapOf<View, Boolean>()
    private var closestViewIndex = -1

    override fun onInterceptTouchEvent(ev: MotionEvent): Boolean {
        if (ev.action == MotionEvent.ACTION_DOWN) {
            handleMotionEventDown(ev)
        }
        if (ev.action == MotionEvent.ACTION_MOVE) {
            return true
        }
        return super.onInterceptTouchEvent(ev)
    }

    @SuppressLint("ClickableViewAccessibility")
    override fun onTouchEvent(event: MotionEvent): Boolean {
        if (!children.any()) {
            return super.onTouchEvent(event)
        }
        when(event.action) {
            MotionEvent.ACTION_DOWN -> {
                // 拖动起始点不在一个child上，也选择一个最近的View
                // handleMotionEventDown(event)
                // return true
            }
            MotionEvent.ACTION_MOVE -> {
                handleMotionEventMove(event)
                return true
            }
            MotionEvent.ACTION_UP -> {
                childrenSelectionOnMoveStart.clear()
                return true
            }
            MotionEvent.ACTION_CANCEL -> {
                childrenSelectionOnMoveStart.clear()
                return true
            }
        }
        return super.onTouchEvent(event)
    }

    private fun handleMotionEventDown(event: MotionEvent) {
        children.forEachIndexed { index, view ->
            // 记录所有Chip的选中状态
            childrenSelectionOnMoveStart[view] = view.isSelected
            // 查找距离起始点最近的View
            closestViewIndex = findClosestViewIndex(event.x.roundToInt(), event.y.roundToInt())
        }
    }

    private fun handleMotionEventMove(event: MotionEvent) {
        val startViewIndex = closestViewIndex
        val endViewIndex = findClosestViewIndex(event.x.roundToInt(), event.y.roundToInt())

        val range = min(startViewIndex, endViewIndex)..max(startViewIndex, endViewIndex)
        for (i in 0 until childCount) {
            val view = getChildAt(i)
            val originSelection = childrenSelectionOnMoveStart[view] == true
            view.isSelected = if (i in range) {
                // 反选拖动区域所有View的选中状态
                !originSelection
            } else {
                // 不在拖动区域，还原到初始选择状态
                originSelection
            }
        }
    }

    private fun findClosestViewIndex(x: Int, y: Int): Int {
        var finalViewIndex = -1
        val rect = Rect()
        var distance = Int.MAX_VALUE
        children.forEachIndexed { index, view ->
            view.getHitRect(rect)
            val d = getDistanceBetweenRectAndPoint(rect, x, y)
            if (d < distance) {
                distance = d
                finalViewIndex = index
            }
        }
        return finalViewIndex
    }

    private fun getDistanceBetweenRectAndPoint(rect: Rect, x: Int, y: Int): Int {
        val xDistance = if (x in rect.left..rect.right) {
            0
        } else (
            min(abs(x - rect.left), abs(x - rect.right))
        )
        val yDistance = if (y in rect.top..rect.bottom) {
            0
        } else {
            min(abs(y - rect.top), abs(y - rect.bottom))
        }
        return sqrt((xDistance * xDistance + yDistance * yDistance).toFloat()).roundToInt()
    }
}