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

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void eingabeB_Click(object sender, EventArgs e)
        {
            Form2 form = new Form2();
            form.Show();
            MessageBox.Show("Bla Blub", "Titel", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
        }
        
        private void treeView1_AfterSelect(object sender, TreeViewEventArgs e)
        {
            DriveInfo[] drives = DriveInfo.GetDrives();

            foreach (DriveInfo item in drives)
            {
                DirectoryInfo di = item.RootDirectory;
                FileInfo[] files = di.GetFiles();

                try
                {
                    files = di.GetFiles();

                    foreach (FileInfo fi in files)
                    { Console.WriteLine(fi.FullName); }
                }
                catch (Exception ex)
                {
                    Logger.LogData("Fehler beim Auslesen der Dateien.Exception Verzeichnis: " + item.RootDirectory); continue;
                }

                foreach (DirectoryInfo di2 in di.GetDirectories())
                {
                    Laufwerke.Nodes.Add(new TreeNode(di2.FullName));
                    di2.GetFiles();
                }
            }
        }
    }
}					

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public Form1()
{
    InitializeComponent();

    ReadDrives();
}

private void ReadDrives()
{
  // hier der Code aus dem bisherigen AfterSelect-Ereignis
}