Get Registered File Types and Their Associated Icons in C#

using System;
using System.Collections.Generic;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

namespace FileTypeAndIcon
{
    public partial class IconForm : Form
    {
        #region PROPERTIES

        /// <summary>
        /// Used for containing file types and thier icons information.
        /// </summary>
        private Hashtable icons;

        /// <summary>
        /// USed for getting registered file types and their icons information.
        /// </summary>
        private RegisteredFileType fileType;

        #endregion

        #region CONSTRUCTORS

        public IconForm()
        {
            InitializeComponent();
            this.fileType = new RegisteredFileType();
        }

        #endregion

        #region GUI EVENTS

        private void IconForm_Load(object sender, EventArgs e)
        {
            try
            {
                //Gets file type and icon info.
                this.icons = this.fileType.GetFileTypeAndIcon();

                //Loads file types to ListBox.
                foreach (object objString in this.icons.Keys)
                {
                    this.lbxFileType.Items.Add(objString);
                }
            }
            catch (Exception exc)
            {
                MessageBox.Show(exc.Message);
            }
        }

        private void btnSearch_Click(object sender, EventArgs e)
        {
            if (string.IsNullOrEmpty(this.txtSearch.Text.Trim()))
                return;
            string searchName = "";
            if (!this.txtSearch.Text.Contains("."))
                searchName = "." + this.txtSearch.Text; //Add a dot if the search text does not have it.
            else
                searchName = this.txtSearch.Text;

            //Searches in the collections of file types and icons.
            object objName = this.icons[searchName];
            if (objName != null)
            {
                this.lbxFileType.SelectedItem = searchName;
            }
        }

        private void lbxFileType_SelectedIndexChanged(object sender, EventArgs e)
        {
            try
            {
                if (this.lbxFileType.Items.Count <= 0 || this.lbxFileType.SelectedItem == null)
                    return;
                string fileType = this.lbxFileType.SelectedItem.ToString();
                this.showIcon(fileType);
            }
            catch (Exception exc)
            {
                MessageBox.Show(exc.Message);
            }
        }

        private void txtSearch_TextChanged(object sender, EventArgs e)
        {
            if (string.IsNullOrEmpty(this.txtSearch.Text.Trim()))
            {
                this.btnSearch.Enabled = false;
            }
            else
            {
                this.btnSearch.Enabled = true;
            }
        }

        /// <summary>
        /// Shows the icon associates with a specific file type.
        /// </summary>
        /// <param name="fileType">The type of file (or file extension).</param>
        private void showIcon(string fileType)
        {
            try
            {
                string fileAndParam = (this.icons[fileType]).ToString();
                if (String.IsNullOrEmpty(fileAndParam))
                    return;

                //Use to store the file contains icon.
                string fileName = "";

                //The index of the icon in the file.
                int iconIndex = 0;
                string iconIndexString = "";

                int index = fileAndParam.IndexOf(",");
                //if fileAndParam is some thing likes that: "C:\\Program Files\\NetMeeting\\conf.exe,1".
                if (index > 0)
                {
                    fileName = fileAndParam.Substring(0, index);
                    iconIndexString = fileAndParam.Substring(index + 1);
                }
                else
                    fileName = fileAndParam;

                if (!string.IsNullOrEmpty(iconIndexString))
                {
                    //Get the index of icon.
                    iconIndex = int.Parse(iconIndexString);
                    if (iconIndex < 0)
                        iconIndex = 0;  //To avoid the invalid index.
                }

                //Gets the handle of the icon.
                IntPtr lIcon = RegisteredFileType.ExtractIcon(this.Handle.ToInt32(), fileName, iconIndex);

                //The handle cannot be zero.
                if (lIcon != IntPtr.Zero)
                {
                    //Gets the real icon.
                    Icon icon = Icon.FromHandle(lIcon);

                    //Draw the icon to the picture box.
                    this.pbIconView.Image = icon.ToBitmap();
                }
                else //if the icon is invalid, show an error image.
                    this.pbIconView.Image = this.pbIconView.ErrorImage;
            }
            catch (Exception exc)
            {
                throw exc;
            }
        }

        #endregion
    }
}

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