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

namespace HorizontallyScrollingComboBox
{
  public partial class ComboBox : System.Windows.Forms.ComboBox
  {
    // Example project demonstrating applying a horizontal scrollbar to a standard combobox
    // Original article and more at http://cyotek.com

    #region  Private Member Declarations  

    private const int CB_SETHORIZONTALEXTENT = 0x015E;
    private const int WS_HSCROLL = 0x100000;

		#endregion  Private Member Declarations  

		#region  Private Class Methods  

    [DllImport("user32.dll")]
    private static extern IntPtr SendMessage(IntPtr hWnd, UInt32 msg, IntPtr wParam, IntPtr lParam);

		#endregion  Private Class Methods  

		#region  Public Methods  

    public void SetHorizontalExtent()
    {
      int maxWith;

      maxWith = 0;
      foreach (object item in this.Items)
      {
        Size textSize;

        textSize = TextRenderer.MeasureText(item.ToString(), this.Font);
        if (textSize.Width > maxWith)
          maxWith = textSize.Width;
      }

      this.SetHorizontalExtent(maxWith);
    }

    public void SetHorizontalExtent(int width)
    {
      SendMessage(this.Handle, CB_SETHORIZONTALEXTENT, new IntPtr(width), IntPtr.Zero);
    }

		#endregion  Public Methods  

		#region  Protected Properties  

    protected override CreateParams CreateParams
    {
      get
      {
        CreateParams createParams;

        createParams = base.CreateParams;
        createParams.Style |= WS_HSCROLL;

        return createParams;
      }
    }

		#endregion  Protected Properties  
  }
}