组合框下拉位置

棘手的问题。我找不到解决这个问题的好办法,只有一个变通办法。添加一个新类并粘贴下面显示的代码。编译。将新控件从工具箱顶部放到窗体上。

解决办法不是很好。问题是下拉窗口将忽略移动它的尝试,直到下拉动画完成。视觉效果不是很好,你会看到窗口向下,然后跳到左边。我不知道用什么方法来拍它的头,也许其他人知道。

C版本:

using System;
using System.Drawing;
using System.Windows.Forms;
using System.Runtime.InteropServices;

public class MyComboBox : ComboBox {
  protected override void OnDropDown(EventArgs e) {
    // Is dropdown off the right side of the screen?
    Point pos = this.PointToScreen(this.Location);
    Screen scr = Screen.FromPoint(pos);
    if (scr.WorkingArea.Right < pos.X + this.DropDownWidth) {
       this.BeginInvoke(new Action(() => {
        // Retrieve handle to dropdown list
        COMBOBOXINFO info = new COMBOBOXINFO();
        info.cbSize = Marshal.SizeOf(info);
        SendMessageCb(this.Handle, 0x164, IntPtr.Zero, out info);
        // Move the dropdown window
        RECT rc;
        GetWindowRect(info.hwndList, out rc);
        int x = scr.WorkingArea.Right - (rc.Right - rc.Left);
        SetWindowPos(info.hwndList, IntPtr.Zero, x, rc.Top, 0, 0, 5);
      }));
    }
    base.OnDropDown(e);
  }

  // P/Invoke declarations
  private struct COMBOBOXINFO {
    public Int32 cbSize;
    public RECT rcItem, rcButton;
    public int buttonState;
    public IntPtr hwndCombo, hwndEdit, hwndList;
  }
  private struct RECT {
    public int Left, Top, Right, Bottom;
  }
  [DllImport("user32.dll", EntryPoint = "SendMessageW", CharSet = CharSet.Unicode)]
  private static extern IntPtr SendMessageCb(IntPtr hWnd, int msg, IntPtr wp, out COMBOBOXINFO lp);
  [DllImport("user32.dll")]
  private static extern bool SetWindowPos(IntPtr hWnd, IntPtr after, int x, int y, int cx, int cy, int flags);
  [DllImport("user32.dll")]
  private static extern bool GetWindowRect(IntPtr hWnd, out RECT rc);
}

VB.NET版本:

Imports System
Imports System.Drawing
Imports System.Windows.Forms
Imports System.Runtime.InteropServices

Public Class MyComboBox
    Inherits ComboBox

    'P/Invoke declarations
    Private Structure COMBOBOXINFO
        Public cbSize As Int32
        Public rcItem As RECT
        Public rcButton As RECT
        Public buttonState As Integer
        Public hwndCombo As IntPtr
        Public hwndEdit As IntPtr
        Public hwndList As IntPtr
    End Structure

    Private Structure RECT
        Public Left As Integer
        Public Top As Integer
        Public Right As Integer
        Public Bottom As Integer
    End Structure


    <DllImport("user32.dll", EntryPoint:="SendMessageW", CharSet:=CharSet.Unicode)>
    Private Shared Function SendMessageCb(hWnd As IntPtr, msg As Integer, wp As IntPtr, ByRef lp As COMBOBOXINFO) As IntPtr
    End Function

    <DllImport("user32.dll")>
    Private Shared Function SetWindowPos(hWnd As IntPtr, after As IntPtr, x As Integer, y As Integer, cx As Integer, cy As Integer, flags As Integer) As Boolean
    End Function

    <DllImport("user32.dll")>
    Private Shared Function GetWindowRect(hWnd As IntPtr, ByRef rc As RECT) As Boolean
    End Function


    Protected Overrides Sub OnDropDown(e As EventArgs)
          ' Is dropdown off the right side of the screen?
          Dim pos As Point = Me.PointToScreen(Me.Location)
          Dim scr As Screen = Screen.FromPoint(pos)

          If (scr.WorkingArea.Right < pos.X + Me.DropDownWidth) Then
              Me.BeginInvoke(New Action(Sub()

                                            'Retrieve handle to dropdown list
                                            Dim info As COMBOBOXINFO = New COMBOBOXINFO()
                                            info.cbSize = Marshal.SizeOf(info)
                                            SendMessageCb(Me.Handle, &H164, IntPtr.Zero, info)
                                            'Move the dropdown window
                                            Dim rc As RECT
                                            GetWindowRect(info.hwndList, rc)
                                            Dim x As Integer = scr.WorkingArea.Right - (rc.Right - rc.Left)
                                            SetWindowPos(info.hwndList, IntPtr.Zero, x, rc.Top, 0, 0, 5)
                                        End Sub))
          End If

          MyBase.OnDropDown(e)

    End Sub



End Class