Android画板开发之基本画笔功能

 class TPView(context: Context,attr:AttributeSet ) : View(context,attr) {


  private var preX: Float = 0.0f //上一次的触摸点x坐标
  private var preY: Float = 0.0f //上一次触摸点y坐标

  var mPath = Path()  //path路径

  //画笔
  private var mPaint = Paint(Paint.ANTI_ALIAS_FLAG or Paint.DITHER_FLAG)

  init {
    //画笔为实心
    mPaint.style = Paint.Style.STROKE
    //颜色
    mPaint.color = Color.RED
    //笔触为圆形
    mPaint.strokeCap = Paint.Cap.ROUND
    //画笔大小
    mPaint.strokeWidth = 10f
    //View的背景颜色
    setBackgroundColor(Color.WHITE)
  }

  override fun onDraw(canvas: Canvas) {
    super.onDraw(canvas)
    //画线
    canvas.drawPath(mPath,mPaint)
  }

  override fun onTouchEvent(event: MotionEvent): Boolean {

    when(event.action){
      MotionEvent.ACTION_DOWN -> { //手指按下的时候
        //将起始点移动到当前坐标
        mPath.moveTo(event.x,event.y)
        //记录上次触摸的坐标，注意ACTION_DOWN方法只会执行一次
        preX = event.x
        preY = event.y
      }
      MotionEvent.ACTION_MOVE -> { //手指移动的时候

        //绘制圆滑曲线，即贝塞尔曲线,贝塞尔曲线这个知识自行了解
        mPath.quadTo(preX,preY,event.x,event.y)

        preX = event.x
        preY = event.y
      }
    }

    //重新绘制，会调用onDraw方法
    invalidate()
    return true
  }

}