winform中间画一个方框，鼠标移到方框四点會有小方框可以進行放大縮小方框

你可以通过以下步骤在 WinForms 中实现该功能：

1. 在窗体上添加一个 Panel 控件，设置其 Dock 属性为 Fill，以使其充满整个窗体。
2. 在 Panel 控件上重载 OnPaint 方法，在 OnPaint 方法中使用 Graphics 对象绘制一个矩形框。
3. 在 Panel 控件上订阅 MouseDown、MouseMove 和 MouseUp 事件。在 MouseDown 事件中记录鼠标点击位置，并判断是否在矩形框内。如果是，则设置一个标志位表示正在调整矩形框大小。在 MouseMove 事件中根据标志位判断是否需要调整矩形框大小，并更新矩形框的位置和大小。在 MouseUp 事件中取消标志位。
4. 在 Panel 控件上绘制四个小矩形框，分别表示矩形框的四个角。在 MouseMove 事件中判断鼠标是否在小矩形框内，如果是，则设置一个标志位表示正在调整矩形框大小。在 MouseUp 事件中取消标志位。
5. 在 MouseMove 事件中根据标志位判断是否需要调整小矩形框大小，并更新矩形框的位置和大小。

下面是示例代码：

public partial class Form1 : Form
{
    private Rectangle rect;
    private bool isDragging;
    private bool isResizing;
    private Point startPoint;
    private int resizeHandleSize = 8;

    public Form1()
    {
        InitializeComponent();
        rect = new Rectangle(100, 100, 200, 150);
        panel1.Paint += Panel1_Paint;
        panel1.MouseDown += Panel1_MouseDown;
        panel1.MouseMove += Panel1_MouseMove;
        panel1.MouseUp += Panel1_MouseUp;
    }

    private void Panel1_Paint(object sender, PaintEventArgs e)
    {
        ControlPaint.DrawBorder(e.Graphics, rect, Color.Black, ButtonBorderStyle.Solid);
        DrawResizeHandles(e.Graphics, rect);
    }

    private void Panel1_MouseDown(object sender, MouseEventArgs e)
    {
        if (rect.Contains(e.Location))
        {
            isDragging = true;
            startPoint = e.Location;
        }
        else if (IsOverResizeHandle(e.Location))
        {
            isResizing = true;
            startPoint = e.Location;
        }
    }

    private void Panel1_MouseMove(object sender, MouseEventArgs e)
    {
        if (isDragging)
        {
            int dx = e.Location.X - startPoint.X;
            int dy = e.Location.Y - startPoint.Y;
            rect.X += dx;
            rect.Y += dy;
            panel1.Invalidate();
            startPoint = e.Location;
        }
        else if (isResizing)
        {
            int dx = e.Location.X - startPoint.X;
            int dy = e.Location.Y - startPoint.Y;
            if (IsOverTopLeftHandle(startPoint))
            {
                rect.X += dx;
                rect.Width -= dx;
                rect.Y += dy;
                rect.Height -= dy;
            }
            else if (IsOverTopRightHandle(startPoint))
            {
                rect.Width += dx;
                rect.Y += dy;
                rect.Height -= dy;
            }
            else if (IsOverBottomLeftHandle(startPoint))
            {
                rect.X += dx;
                rect.Width -= dx;
                rect.Height += dy;
            }
            else if (IsOverBottomRightHandle(startPoint))
            {
                rect.Width += dx;
                rect.Height += dy;
            }
            panel1.Invalidate();
            startPoint = e.Location;
        }
        else if (IsOverResizeHandle(e.Location))
        {
            Cursor = Cursors.SizeNWSE;
        }
        else
        {
            Cursor = Cursors.Default;
        }
    }

    private void Panel1_MouseUp(object sender, MouseEventArgs e)
    {
        isDragging = false;
        isResizing = false;
    }

    private bool IsOverResizeHandle(Point p)
    {
        return IsOverTopLeftHandle(p) || IsOverTopRightHandle(p) || IsOverBottomLeftHandle(p) || IsOverBottomRightHandle(p);
    }

    private bool IsOverTopLeftHandle(Point p)
    {
        return new Rectangle(rect.X - resizeHandleSize, rect.Y - resizeHandleSize, resizeHandleSize * 2, resizeHandleSize * 2).Contains(p);
    }

    private bool IsOverTopRightHandle(Point p)
    {
        return new Rectangle(rect.Right - resizeHandleSize, rect.Y - resizeHandleSize, resizeHandleSize * 2, resizeHandleSize * 2).Contains(p);
    }

    private bool IsOverBottomLeftHandle(Point p)
    {
        return new Rectangle(rect.X - resizeHandleSize, rect.Bottom - resizeHandleSize, resizeHandleSize * 2, resizeHandleSize * 2).Contains(p);
    }

    private bool IsOverBottomRightHandle(Point p)
    {
        return new Rectangle(rect.Right - resizeHandleSize, rect.Bottom - resizeHandleSize, resizeHandleSize * 2, resizeHandleSize * 2).Contains(p);
    }

    private void DrawResizeHandles(Graphics g, Rectangle rect)
    {
        g.FillRectangle(Brushes.White, new Rectangle(rect.X - resizeHandleSize, rect.Y - resizeHandleSize, resizeHandleSize * 2, resizeHandleSize * 2));
        g.FillRectangle(Brushes.White, new Rectangle(rect.Right - resizeHandleSize, rect.Y - resizeHandleSize, resizeHandleSize * 2, resizeHandleSize * 2));
        g.FillRectangle(Brushes.White, new Rectangle(rect.X - resizeHandleSize, rect.Bottom - resizeHandleSize, resizeHandleSize * 2, resizeHandleSize * 2));
        g.FillRectangle(Brushes.White, new Rectangle(rect.Right - resizeHandleSize, rect.Bottom - resizeHandleSize, resizeHandleSize * 2, resizeHandleSize * 2));
    }
}