Android 画板 多指操控 多指绘图

• 前言
• 一、思路
• 二、效果展示
• 三：完整代码

是否可以做一个画板，多根手指可以同时绘图，手指移开，移开手指对应的绘图路径也跟着消失

①：每根手指对应一个path，记录手指移动时的路径

val actionIndex = event.actionIndex
val path = Path()
path.moveTo(event.getX(actionIndex), event.getY(actionIndex))

②：创建一个map，让pointerID作为key,path作为value，分开记录每根手指对应的路径

private val paths = SparseArray()

③：每当有手指点下时，map中就新增一个路径

paths.put(event.getPointerId(actionIndex), path)

④：有手指移开时，就把这根手指对应的路径从map中移除

paths.remove(event.getPointerId(event.actionIndex))

⑤：触发MotionEvent.ACTION_MOVE时，遍历每根手指对应的path，把路径引导到手指移动后所在的位置

for (i in 0 until paths.size()) {
    val pointerID = paths.keyAt(i)
    val pointerIndex = event.findPointerIndex(pointerID)
    paths.get(pointerID).lineTo(event.getX(pointerIndex), event.getY(pointerIndex))
}

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package com.lbj23.customview.customview

import android.content.Context
import android.graphics.Canvas
import android.graphics.Paint
import android.graphics.Path
import android.util.AttributeSet
import android.util.SparseArray
import android.view.MotionEvent
import android.view.View
import com.lbj23.customview.dp

class DrawBoardView(context: Context?, attrs: AttributeSet?) : View(context, attrs) {
    private val paint = Paint(Paint.ANTI_ALIAS_FLAG)
    private val paths = SparseArray()

    init {
        paint.apply {
            style = Paint.Style.STROKE
            strokeWidth = 4.dp
            strokeCap = Paint.Cap.ROUND
            strokeJoin = Paint.Join.ROUND
        }
    }

    override fun onDraw(canvas: Canvas) {
        super.onDraw(canvas)
        for (i in 0 until paths.size()) {
            canvas.apply {
                drawPath(paths.get(paths.keyAt(i)), paint)
            }
        }
    }

    override fun onTouchEvent(event: MotionEvent): Boolean {
        when (event.actionMasked) {
            MotionEvent.ACTION_POINTER_DOWN, MotionEvent.ACTION_DOWN -> {
                val actionIndex = event.actionIndex
                val path = Path()
                path.moveTo(event.getX(actionIndex), event.getY(actionIndex))
                paths.put(event.getPointerId(actionIndex), path)
                invalidate()
            }
            MotionEvent.ACTION_MOVE -> {
                for (i in 0 until paths.size()) {
                    val pointerID = paths.keyAt(i)
                    val pointerIndex = event.findPointerIndex(pointerID)
                    paths.get(pointerID).lineTo(event.getX(pointerIndex), event.getY(pointerIndex))
                }
                invalidate()
            }
            MotionEvent.ACTION_POINTER_UP, MotionEvent.ACTION_UP -> {
                paths.remove(event.getPointerId(event.actionIndex))
                invalidate()
            }
        }
        return true
    }
}