ViewDragHelper练习

package com.wuhongru.workman.myView

import android.content.Context
import android.util.AttributeSet
import android.view.MotionEvent
import android.view.View
import android.view.ViewGroup
import androidx.core.view.ViewCompat
import androidx.core.view.children
import androidx.customview.widget.ViewDragHelper

private const val ROWS = 3
private const val COLUMNS = 2

class DragView(context: Context, attrs: AttributeSet) : ViewGroup(context, attrs) {
    private val dragHelper = ViewDragHelper.create(this, DragCallback())

    override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
        val specWidth = MeasureSpec.getSize(widthMeasureSpec)
        val specHeight = MeasureSpec.getSize(heightMeasureSpec)
        val childWidth = specWidth / COLUMNS
        val childHeight = specHeight / ROWS
        measureChildren(MeasureSpec.makeMeasureSpec(childWidth, MeasureSpec.EXACTLY),
            MeasureSpec.makeMeasureSpec(childHeight, MeasureSpec.EXACTLY))
        setMeasuredDimension(specWidth, specHeight)
    }

    override fun onLayout(changed: Boolean, l: Int, t: Int, r: Int, b: Int) {
        var childLeft: Int
        var childTop: Int
        val childWidth = width / COLUMNS
        val childHeight = height / ROWS
        for ((index, child) in children.withIndex()) {
            childLeft = index % 2 * childWidth
            childTop = index / 2 * childHeight
            child.layout(childLeft, childTop, childLeft + childWidth, childTop + childHeight)
        }
    }

    override fun onInterceptTouchEvent(ev: MotionEvent): Boolean {
        return dragHelper.shouldInterceptTouchEvent(ev)
    }

    override fun onTouchEvent(event: MotionEvent): Boolean {
        dragHelper.processTouchEvent(event)
        return true
    }

    override fun computeScroll() {
        if (dragHelper.continueSettling(true)) {
            ViewCompat.postInvalidateOnAnimation(this)
        }
    }


    private inner class DragCallback : ViewDragHelper.Callback() {
        var captureX = 0f
        var captureY = 0f

        override fun tryCaptureView(child: View, pointerId: Int): Boolean {
            if(dragHelper.viewDragState == ViewDragHelper.STATE_SETTLING){
                return false
            }
                return true
        }

        override fun clampViewPositionHorizontal(child: View, left: Int, dx: Int): Int {
            return left
        }

        override fun clampViewPositionVertical(child: View, top: Int, dy: Int): Int {
            return top
        }

        override fun onViewCaptured(capturedChild: View, activePointerId: Int) {
            capturedChild.elevation = elevation + 1
            captureX = capturedChild.left.toFloat()
            captureY = capturedChild.top.toFloat()
        }

        override fun onViewReleased(releasedChild: View, xvel: Float, yvel: Float) {
            dragHelper.settleCapturedViewAt(captureX.toInt(), captureY.toInt())
            postInvalidateOnAnimation()
        }

        override fun onViewDragStateChanged(state: Int) {
            if(state == ViewDragHelper.STATE_IDLE){
                dragHelper.capturedView?.let {
                    it.elevation--
                }
            }

        }
    }
}