winform 鼠标拖动圈选区域

效果展示

需要三个鼠标的时间来配合

//定义全局变量
		int x;
        int y;
        bool isMouthDown = false;
        int width;
        int height;
        Graphics g;

		// 给窗体  加 鼠标点击 MouseDown 事件
        private void Form2_MouseDown(object sender, MouseEventArgs e)//MouseEventArgs 获取鼠标位置
        {
            x = e.X;
            y = e.Y;
            // true 开始
            isMouthDown = true;
        }
		//给窗体  加 鼠标移动 MouseMove事件  
        private void Form2_MouseMove(object sender, MouseEventArgs e)
        {
            if (isMouthDown)
            {
                width = Math.Abs(e.X - x);
                height = Math.Abs(e.Y - y);
                //创建类似画板
                g = CreateGraphics();
                g.Clear(BackColor);
                g.FillRectangle(Brushes.CornflowerBlue, //颜色
                    x < MousePosition.X ? x : e.X, 
                    y < MousePosition.Y ? y : e.Y, 
                    width, height);
            }
        }
		//给窗体  加 鼠标松开 MouseUp事件  
        private void Form2_MouseUp(object sender, MouseEventArgs e)
        {
            width = Math.Abs(e.X - x);
            height = Math.Abs(e.Y - y);
            //创建类似画板
            g = CreateGraphics();
            g.Clear(BackColor);
            g.FillRectangle(Brushes.CornflowerBlue, //颜色
                x < MousePosition.X ? x : e.X,
                y < MousePosition.Y ? y : e.Y,
                width, height);
            isMouthDown = false;
        }