在我的Paint程序中绘制矩形时出错

public partial class Form1 : Form { Point downPoint , upPoint; List shapes = new List(); public ShapesEnum shapeType; public Form1() { InitializeComponent(); } protected override void OnPaint(PaintEventArgs e) { base.OnPaint(e); foreach (var s in shapes) s.Draw(e.Graphics); } protected override void OnMouseDown(MouseEventArgs e) { downPoint = e.Location; } protected override void OnMouseUp(MouseEventArgs e) { base.OnMouseUp(e); upPoint = e.Location; CreateShape(); this.Invalidate(); } private void CreateShape() { if (shapeType == ShapesEnum.Circle) { Rectangle rect = new Rectangle(downPoint.X, downPoint.Y, upPoint.X - downPoint.X, upPoint.Y - downPoint.Y); Ellipse ellipse = new Ellipse() { rect = rect }; shapes.Add(ellipse); } else if (shapeType == ShapesEnum.Rectangle) { Rectangle rect = new Rectangle(downPoint.X, downPoint.Y, upPoint.X - downPoint.X, upPoint.Y - downPoint.Y); Rect rectangle = new Rect() { rect = rect }; shapes.Add(rectangle); } else if (shapeType == ShapesEnum.Line) { Point pt1 = new Point (upPoint.X, upPoint.Y); Point pt2 = new Point (downPoint.X, downPoint.Y); Ln rectangle = new Ln() { PointUp = pt1, PointDown = pt2 }; shapes.Add(rectangle); } lblStatus.Text = string.Format("dn:{0} up:{1} ct:{2}", downPoint, upPoint, shapes.Count()); } private void btnCircle_Click(object sender, EventArgs e) { shapeType = ShapesEnum.Circle; } private void btnRectangle_Click(object sender, EventArgs e) { shapeType = ShapesEnum.Rectangle; } private void btnLine_Click(object sender, EventArgs e) { shapeType = ShapesEnum.Line; } } 

这是我的绘画程序的主要部分。

 public enum ShapesEnum { Circle, Rectangle, Line } abstract class Shapes { public Rectangle rect { get; set; } public Color color { get; set; } public bool isFilled { get; set; } public abstract void Draw(Graphics g); } class Ellipse : Shapes { public override void Draw(Graphics g) { g.DrawEllipse(Pens.Black, rect); } } class Rect : Shapes { public override void Draw(Graphics g) { g.DrawRectangle(Pens.Black, rect); } } class Ln : Shapes { public Point PointUp { get; set; } public Point PointDown { get; set; } public override void Draw(Graphics g) { g.DrawLine(Pens.Black, PointUp, PointDown); } } 

这是我的类，用于在形状上inheritance。 根据形状，将调用其中一个类。

---

绘图椭圆形工作正常。 绘制线也一样。 但是，在绘制矩形方面存在一个错误。 如果我把鼠标拖动并从左到右放开，这将有效。 但是，如果我转向另一个方向，它在窗体上是不可见的，但shapes.Count()仍然会添加到shapes列表中。

是什么导致了这个bug？

Answer 1

尝试这样的事情，以便以正确的方式获得起点和终点：

 int x0 = Math.Min(upPoint.X, downPoint.X); int y0 = Math.Min(upPoint.Y, downPoint.Y); Point upperLeft = new Point(x0, y0); int x1 = Math.Max(upPoint.X, downPoint.X); int y1 = Math.Max(upPoint.Y, downPoint.Y); Point lowerRight = new Point(x1, y1); 

和

 Rectangle rect = new Rectangle(x0, y0, x1 - x0, y1 - y0);