data class PaintData(
    var mPaint: Paint,  //保存畫(huà)筆

    var mPath: Path     //保存路徑
) {
  /**
   * 撤銷和反撤銷之后 重新繪制
   * @param canvas 繪制的畫(huà)布
   */
  fun draw(canvas: Canvas){
    canvas.drawPath(mPath,mPaint)
  }

}

/**
   * 清空畫(huà)布
   * @param isClearList 時(shí)候清空數(shù)據(jù)列表
*/
  fun clear(isClearList:Boolean) {
    if(isClearList){
      mRevokedList.clear()
      mPaintedList.clear()
    }
    mBufferCanvas.drawColor(0, PorterDuff.Mode.CLEAR)
    invalidate()
  }

//儲(chǔ)存已經(jīng)寫(xiě)的筆畫(huà)
private var mPaintedList: MutableList<PaintData> = ArrayList<PaintData>()

//已經(jīng)撤銷的列表
private var mRevokedList: MutableList<PaintData> = ArrayList<PaintData>()

//固化層，超出最大筆畫(huà)就先繪制到這個(gè)層
private lateinit var mHoldBitmap: Bitmap
private lateinit var mHoldCanvas: Canvas

//最多記錄20畫(huà)筆跡
private val MAX_PAINT_RECORED = 20 


  //在測(cè)量的時(shí)候進(jìn)行初始化：
  override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
    if(mBufferCanvas == null){
      mBufferBitmap = Bitmap.createBitmap(measuredWidth, measuredHeight, Bitmap.Config.ARGB_8888)

      //canvas繪制的內(nèi)容，將會(huì)在這個(gè)mBufferBitmap內(nèi)
      mBufferCanvas = Canvas(mBufferBitmap)
    }


    if(mHoldCanvas == null){
      mHoldBitmap = Bitmap.createBitmap(measuredWidth, measuredHeight, Bitmap.Config.ARGB_8888)
      mHoldCanvas = Canvas(mHoldBitmap)
    }
  }

/**
 * 撤回一個(gè)筆跡
 * @return 是否撤回成功
*/
  fun revoked(){
    reDraw(mPaintedList)
  }

 /**
   * 反撤回一個(gè)筆跡
   */
  fun unRevoked(){
    reDraw(mRevokedList)
}

/**
   * 重新繪制
   * @param paintList 需要操作的list
 */
  private fun reDraw(paintList:MutableList<PaintData>){

    if(paintList.size > 0){
      val paint = paintList.removeAt(paintList.size-1)
      if(paintList === mPaintedList){
        mRevokedList.add(paint)
      }else{
        mPaintedList.add(paint)
      }

      //清空緩存畫(huà)板
      mBufferCanvas.drawColor(0, PorterDuff.Mode.CLEAR)

      invalidate()

    }
  }

override fun onTouchEvent(event: MotionEvent): Boolean {

    when(event.action){
      MotionEvent.ACTION_DOWN -> { //手指按下的時(shí)候
        //將起始點(diǎn)移動(dòng)到當(dāng)前坐標(biāo)
        mPath.moveTo(event.x,event.y)

        //記錄上次觸摸的坐標(biāo)，注意ACTION_DOWN方法只會(huì)執(zhí)行一次
        preX = event.x
        preY = event.y

        //保存畫(huà)筆
        mPaintedList.add(PaintData(Paint(mPaint),Path(mPath)))

      }
      MotionEvent.ACTION_MOVE -> { //手指移動(dòng)的時(shí)候

        //繪制圓滑曲線，即貝塞爾曲線,貝塞爾曲線這個(gè)知識(shí)自行了解
        mPaintedList.get(mPaintedList.size-1).mPath.quadTo(preX,preY,event.x,event.y)

        //重新繪制，會(huì)調(diào)用onDraw方法
        invalidate()

        preX = event.x
        preY = event.y
      }
      MotionEvent.ACTION_UP ->{

        //清除路徑的內(nèi)容
        mPath.reset()

      }
    }

    // true：告訴系統(tǒng)，這個(gè)觸摸事件由我來(lái)處理
    // false：告訴系統(tǒng)，這個(gè)觸摸事件我不處理，這時(shí)系統(tǒng)會(huì)把觸摸事件傳遞給imageview的父節(jié)點(diǎn)
    return true
  }

override fun onDraw(canvas: Canvas) {
    super.onDraw(canvas)


    //超出緩存的就固化到緩存bitmap
    while(mPaintedList.size > MAX_PAINT_RECORED){
      val paintData = mPaintedList.removeAt(0)
      paintData.draw(mHoldCanvas)
    }

    //繪制固化的內(nèi)容到緩存Canvas
    mBufferCanvas.drawBitmap(mHoldBitmap,0f,0f,null)

    //繪制記錄的畫(huà)筆
    for(paint in mPaintedList){
      //重新繪制每個(gè)path
      paint.draw(mBufferCanvas)
    }


    //畫(huà)出緩存bitmap的內(nèi)容
    canvas.drawBitmap(mBufferBitmap,0f,0f,null)

  }

/**
   * 清空畫(huà)布
*/
  fun clear() {
    mRevokedList.clear()
    mPaintedList.clear()
    mHoldCanvas.drawColor(0, PorterDuff.Mode.CLEAR)
    mBufferCanvas.drawColor(0, PorterDuff.Mode.CLEAR)
    invalidate()

  }