想实现随着鼠标的拖动，画出椭圆，好像就差一点了。。。

[苦茶爷爷]

public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        Point P1 = new Point();
        Point P2 = new Point();
        bool isMouseDown = false;

        private void Form1_MouseUp(object sender, MouseEventArgs e)
        {
            isMouseDown = false;
            
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            
        }

        private void Form1_Paint(object sender, PaintEventArgs e)
        {

            Graphics g = e.Graphics;
          //  Rectangle rect1 = new Rectangle(P1.X, P1.Y, P2.Y - P1.Y, P2.Y - P1.Y);
           // Rectangle rect1 = new Rectangle(1, 1, 100, 100);
            DrawTY(g, P1.X, P1.Y, P2.Y - P1.Y, P2.Y - P1.Y);
        }

        private void DrawTY(Graphics g, int a,int b,int c,int d )
        {
            GraphicsPath roundedRect = new GraphicsPath();
            roundedRect.AddArc(a, b, c, d, 0, 360);
            roundedRect.CloseFigure();

            //从路径中创建区域
            Region pathRegion = new Region(roundedRect);
           // g.FillRegion(new SolidBrush(Color.Blue), pathRegion);
            g.DrawPath(Pens.Blue, roundedRect);

        }

        private void Form1_MouseDown(object sender, MouseEventArgs e)
        {
            if (isMouseDown == false)
            {
                isMouseDown = true;

                P1.X = e.X;
                P1.Y = e.Y;
            }
        }

        private void Form1_MouseMove(object sender, MouseEventArgs e)
        {
            if (isMouseDown == true)
            {

                P2.X = e.X;
                P2.Y = e.Y;

                this.Invalidate();
            }
        }
    }

我调用DrawTY函数，传入几个值，但是报错

为什么，我直接绘制椭圆是好的，但是通过获取坐标来绘制有问题呢？

[苦茶爷爷]

请问还有人帮帮忙吗？

[苦茶爷爷]

自己顶！！！！

[苦茶爷爷]

请大家回复一下哈，谢谢！

[小猪八Q]

        private void Form1_MouseMove(object sender, MouseEventArgs e)
        {
            if (isMouseDown == true)
            {

                P2.X = e.X;
                P2.Y = e.Y;
                DrawTY(this.CreateGraphics(), P2.X, P2.Y, 100, 100);
                this.Invalidate();
            }
        }

修改了下你的代码，在MouseMove中加入了Move的事件，这样才能看到圆，当然在窗体重绘过程中就有消失了，所以是闪烁的，但是并没有出现你所说的问题

[苦茶爷爷]

 public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        Point P1 = new Point();
        Point P2 = new Point();
        bool isMouseDown = false;

        private void Form1_MouseUp(object sender, MouseEventArgs e)
        {
            isMouseDown = false;
            
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            
        }

        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            
            Graphics g = e.Graphics;

        //    g.DrawEllipse(new Pen(Color.Red, 3), 1, 1, 5, 5);
            g.DrawRectangle(new Pen(Color.Blue, 3), P1.X > P2.X ? P2.X : P1.X, P1.Y > P2.Y ? P2.Y : P1.Y, Math.Abs(P2.X - P1.X), Math.Abs(P2.Y - P1.Y));

            
        }

        

        private void Form1_MouseDown(object sender, MouseEventArgs e)
        {
            if (isMouseDown == false)
            {
                isMouseDown = true;

                P1.X = e.X;
                P1.Y = e.Y;
            }
        }

        private void Form1_MouseMove(object sender, MouseEventArgs e)
        {
            if (isMouseDown == true)
            {

                P2.X = e.X;
                P2.Y = e.Y;

                this.Invalidate();
            }
        }
    }

谢谢上面的同学，但是还有问题。 大家看我上面那一行代码，可以实现矩形的。