C# 3.0 如何使用鼠标在C#中绘制矩形

我想用C#在一个窗体上画一个矩形。我读了之后发现了这个。是否有任何示例或教程可用？这篇文章并不是很有帮助。

链接的文章看起来是C++，这可能解释它为什么对你没有多大帮助。 如果为MouseDown和MouseUp创建事件，则应该具有矩形所需的两个角点。从这里开始，这是一个在表单上绘制的问题。System.Drawing.*可能是您的第一站。下面链接了几个教程：

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您需要这3个函数和变量：

    private Graphics g;
    Pen pen = new System.Drawing.Pen(Color.Blue, 2F);
    private Rectangle rectangle;
    private int posX, posY, width, height; 

其次，您需要创建鼠标按下事件：

    private void pictureCrop_MouseDown(object sender, MouseEventArgs e)
    {
        if (e.Button == MouseButtons.Left)
        {
            posX = e.X;
            posY = e.Y;
        }
    }

第三，您需要实现鼠标向上移动事件：

    private void pictureCrop_MouseUp(object sender, MouseEventArgs e)
    {
        if (e.Button != MouseButtons.Left)
            return;

        if (e.X > posX && e.Y > posY) // top left to bottom right
        {
            width = Math.Abs(e.X - posX);
            height = Math.Abs(e.Y - posY);
        }
        else if (e.X < posX && e.Y < posY) // bottom right to top left
        {
            width = Math.Abs(posX - e.X);
            height = Math.Abs(posY - e.Y);

            posX = e.X;
            posY = e.Y;
        }
        else if (e.X < posX && e.Y > posY) // top right to bottom left
        {
            width = Math.Abs(posX - e.X);
            height = Math.Abs(posY - e.Y);

            posX = e.X;
        }
        else if (e.X > posX && e.Y < posY) // bottom left to top right
        {
            width = Math.Abs(posX - e.X);
            height = Math.Abs(posY - e.Y);

            posY = e.Y;
        }

        g.DrawImage(_bitmap, 0, 0);
        rectangle = new Rectangle(posX, posY, width, height);
        g = pictureCrop.CreateGraphics();
        g.DrawRectangle(pen, rectangle);
    }

    protected override void OnPaint(PaintEventArgs e)
    {
        base.OnPaint(e);

        Graphics graph = e.Graphics;
        graph.DrawImage(_bitmap, 0, 0);
        Rectangle rec = new Rectangle(posX, posY, width, height);
        graph.DrawRectangle(pen, rec);
    }