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  }}