c# 窗体不能拖拽放大

要实现窗体的拖拽和放大功能，可以在窗体的MouseDown、MouseMove、MouseUp事件中编写相应的代码。下面是一个简单的示例代码，可以实现窗体的拖拽和放大功能。

private const int WM_NCHITTEST = 0x0084;
private const int HTLEFT = 10;
private const int HTRIGHT = 11;
private const int HTTOP = 12;
private const int HTTOPLEFT = 13;
private const int HTTOPRIGHT = 14;
private const int HTBOTTOM = 15;
private const int HTBOTTOMLEFT = 16;
private const int HTBOTTOMRIGHT = 17;

private const int WM_SYSCOMMAND = 0x0112;
private const int SC_SIZE = 0xF000;

private bool isDragging = false;
private Point lastLocation;

protected override void WndProc(ref Message m)
{
    switch (m.Msg)
    {
        case WM_NCHITTEST:
            base.WndProc(ref m);
            if (m.Result.ToInt32() == HTCLIENT)
            {
                Point mouseLocation = PointToClient(Cursor.Position);
                if (mouseLocation.X <= 5)
                    m.Result = new IntPtr(HTLEFT);
                else if (mouseLocation.X >= ClientSize.Width - 5)
                    m.Result = new IntPtr(HTRIGHT);
                else if (mouseLocation.Y <= 5)
                    m.Result = new IntPtr(HTTOP);
                else if (mouseLocation.Y >= ClientSize.Height - 5)
                    m.Result = new IntPtr(HTBOTTOM);
                else if (mouseLocation.X <= 10 && mouseLocation.Y <= 10)
                    m.Result = new IntPtr(HTTOPLEFT);
                else if (mouseLocation.X >= ClientSize.Width - 10 && mouseLocation.Y <= 10)
                    m.Result = new IntPtr(HTTOPRIGHT);
                else if (mouseLocation.X <= 10 && mouseLocation.Y >= ClientSize.Height - 10)
                    m.Result = new IntPtr(HTBOTTOMLEFT);
                else if (mouseLocation.X >= ClientSize.Width - 10 && mouseLocation.Y >= ClientSize.Height - 10)
                    m.Result = new IntPtr(HTBOTTOMRIGHT);
            }
            return;
        case WM_SYSCOMMAND:
            if (m.WParam.ToInt32() == SC_SIZE)
            {
                Point mouseLocation = PointToClient(Cursor.Position);
                if (mouseLocation.X <= 5 || mouseLocation.X >= ClientSize.Width - 5)
                    m.WParam = new IntPtr((mouseLocation.Y <= 5) ? HTTOP : HTBOTTOM);
                else if (mouseLocation.Y <= 5 || mouseLocation.Y >= ClientSize.Height - 5)
                    m.WParam = new IntPtr((mouseLocation.X <= 5) ? HTLEFT : HTRIGHT);
            }
            break;
    }
    base.WndProc(ref m);
}

private void Form1_MouseDown(object sender, MouseEventArgs e)
{
    if (e.Button == MouseButtons.Left)
    {
        isDragging = true;
        lastLocation = e.Location;
    }
}

private void Form1_MouseMove(object sender, MouseEventArgs e)
{
    if (isDragging)
    {
        Location = new Point(Location.X - lastLocation.X + e.X, Location.Y - lastLocation.Y + e.Y);
        Update();
    }
}

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

这段代码可以实现以下几个功能：

1. 实现窗体边框的拖拽调整大小功能；
2. 在窗体的左上角、右上角、左下角、右下角调整窗体大小时，鼠标会变成对应的调整大小的光标；
3. 实现窗体的拖拽移动功能。

你可以在窗体的MouseDown、MouseMove、MouseUp事件中分别调用上述代码实现窗体的拖拽和放大功能。