Winform combobox的下拉部分实现触屏上下滑动

Winform combobox默认情况下是不支持触屏上下滑动的，但可以通过自定义控件来实现这个功能。

一种常见的方法是使用自定义的控件去替代原生的Winform combobox控件。这个自定义控件可以继承自ComboBox，并重写其OnDropDown方法，以便在下拉菜单展开时添加一个滚动条。

具体步骤如下：

1. 创建一个新的Winform控件，取名为CustomComboBox。

2. 继承自ComboBox，并重写OnDropDown方法，以便在下拉菜单展开时添加一个滚动条。

   public class CustomComboBox : ComboBox
   {
       protected override void OnDropDown(EventArgs e)
       {
           base.OnDropDown(e);
           var handle = SendMessage(this.Handle, CB_GETCOMBOBOXINFO, IntPtr.Zero, IntPtr.Zero);
           var info = (COMBOBOXINFO)Marshal.PtrToStructure(handle, typeof(COMBOBOXINFO));
           var listBoxHandle = info.hwndList;
           SetWindowLong(listBoxHandle, GWL_STYLE, GetWindowLong(listBoxHandle, GWL_STYLE) | LBS_NOTIFY | WS_VSCROLL);
       }

       private const int CB_GETCOMBOBOXINFO = 0x164;
       private const int GWL_STYLE = -16;
       private const int LBS_NOTIFY = 0x00000001;
       private const int WS_VSCROLL = 0x00200000;

       [DllImport("user32.dll", SetLastError = true)]
       private static extern IntPtr SendMessage(IntPtr hWnd, int Msg, IntPtr wParam, IntPtr lParam);

       [DllImport("user32.dll", SetLastError = true)]
       private static extern int SetWindowLong(IntPtr hWnd, int nIndex, int dwNewLong);

       [StructLayout(LayoutKind.Sequential)]
       private struct COMBOBOXINFO
       {
           public int cbSize;
           public RECT rcItem;
           public RECT rcButton;
           public int stateButton;
           public IntPtr hwndCombo;
           public IntPtr hwndEdit;
           public IntPtr hwndList;
       }

       [StructLayout(LayoutKind.Sequential)]
       private struct RECT
       {
           public int left, top, right, bottom;
       }
   }

3. 在Form中使用CustomComboBox，然后在TouchDown事件中记录当前触屏的坐标。

   public partial class Form1 : Form
   {
       private Point _startPoint;

       public Form1()
       {
           InitializeComponent();
       }

       private void customComboBox1_TouchDown(object sender, TouchEventArgs e)
       {
           _startPoint = e.Location;
       }
   }

4. 在TouchMove事件中计算当前触屏滑动的距离，然后根据距离调整下拉菜单的位置。

   private void customComboBox1_TouchMove(object sender, TouchEventArgs e)
   {
       var distance = e.Location.Y - _startPoint.Y;
       var dropDownHeight = customComboBox1.DropDownHeight;
       if (distance > 0)
       {
           customComboBox1.DropDownHeight = Math.Min(dropDownHeight + distance, customComboBox1.Items.Count * customComboBox1.ItemHeight);
       }
       else
       {
           customComboBox1.DropDownHeight = Math.Max(dropDownHeight + distance, customComboBox1.ItemHeight);
       }
   }

5. 最后，在Form的Load事件中为CustomComboBox的TouchDown和TouchMove事件添加处理程序。

   private void Form1_Load(object sender, EventArgs e)
   {
       customComboBox1.TouchDown += customComboBox1_TouchDown;
       customComboBox1.TouchMove += customComboBox1_TouchMove;
   }

这样，就可以在Winform中实现触屏上下滑动combobox的下拉部分了。