Form5->ListView1->Items->Clear();
    WIN32_FIND_DATA filedata;
    AnsiString slVolumeName;
    DWORD dwVolumeSerial;
    HANDLE filehandle;
    SYSTEMTIME stcUTC,stLocal;
    DWORDLONG filesize;
    int pos,i=0;
    float size;
    String groesse,date,minute,hour,typ,dir=pfad;
    WORD nummer;
    TIcon *MyIcon = new TIcon();

    Form5->ListIcons->Clear();
    Form5->ListIcons->BkColor= (TColor)0x00FFFFFF;    //Transparenz
    Form5->LargeIcons->Clear();
    Form5->LargeIcons->BkColor= (TColor)0x00FFFFFF;    //Transparenz

    if(Tree->IsDiskInDrive(dir,slVolumeName,dwVolumeSerial)){

    filehandle = FindFirstFile((dir+"\\*.*" ).c_str(), &filedata);
    bool found = (filehandle != INVALID_HANDLE_VALUE);
    while (found == true)
    {
        String file=filedata.cFileName;
        if (((filedata.dwFileAttributes & FILE_ATTRIBUTE_HIDDEN) == 0)
            && (file != ".") && (file != "..")){

           TListItem *Subfolder = Form5->ListView1->Items->Add();
           //Dateiname
           Subfolder->Caption=file;
           //Icon
           String lol=dir+"\\"+file;
           lol=ReplaceStr(lol,"\\\\","\\");
           MyIcon->Handle=ExtractAssociatedIcon(Form5->Handle,lol.c_str(),&nummer);
           if(MyIcon->Handle!=NULL)
           {
               Form5->LargeIcons->AddIcon(MyIcon);
               Form5->ListIcons->AddIcon(MyIcon);

           }
           Subfolder->ImageIndex=i;
           i++;

           //FileTime
           FileTimeToSystemTime(&filedata.ftLastWriteTime,&stcUTC);
           SystemTimeToTzSpecificLocalTime(NULL, &stcUTC, &stLocal);
           if(stLocal.wMinute<10){
              minute="0"+IntToStr(stLocal.wMinute);
           }else{
              minute=IntToStr(stLocal.wMinute);
           }
           if(stLocal.wHour<10){
              hour="0"+IntToStr(stLocal.wHour);
           }else{
              hour=IntToStr(stLocal.wHour);
           }
           date=IntToStr(stLocal.wDay)+"."+IntToStr(stLocal.wMonth)+"."+IntToStr(stLocal.wYear)+" "+hour+":"+minute;
           Subfolder->SubItems->Add(date);

           if((filedata.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) ==0){

               //Typ
               pos=LastDelimiter(".",filedata.cFileName);
               typ=String(filedata.cFileName);
               typ=typ.Delete(1,pos);
               if(typ=="Ink"){
                   Subfolder->SubItems->Add("Verknüpfung");
               }else{
                   Subfolder->SubItems->Add(typ+"-Datei");
               }
               //Größe hierher
               size=filedata.nFileSizeLow;
               SetRoundMode(rmDown);
               if(size<1024){
                   groesse=FloatToStr(size)+" Bytes";
               }else if(size>=1024 && size<1048576){
                   size=RoundTo(size/1024,-2);
                   groesse=FloatToStrF(size,ffGeneral,4,DecimalSeparator)+" KB";
               }else if(size>=1048576 && size<1073741824){
                   size=RoundTo(size/1024/1024,-2);
                   groesse=FloatToStrF(size,ffGeneral,4,DecimalSeparator)+" MB";
               }else if(size>=1073741824){ // stimmt das??
                   size=filedata.nFileSizeHigh*4+size/1024/1024/1024;
                   groesse=FloatToStrF(size,ffGeneral,4,DecimalSeparator)+" GB";
               }else{
                   groesse="[Dateigröße konnte nicht bestimmt werden]";
               }

               Subfolder->SubItems->Add(groesse);
           }else{
               Subfolder->SubItems->Add("Verzeichnis");
               Subfolder->SubItems->Add("[-]");
           }
        }
        else
        {
        }
        found = FindNextFile(filehandle, &filedata);

    }
    if(Form5->ListView1->Items->Count!=0){
    Form5->ListView1->Items->operator [](0)->Selected=true;
    Form5->ListView1->Focused();
    }
    FindClose(filehandle);
    DestroyIcon(MyIcon);
    }

Grüße XBert

Wie kann ich das ändern (optimieren)?

Anfangen kannst du, indem du einzelne Abschnitte auskommentierst und mittels wiederholter Durchläufe prüfst, bei welcher Aktion die meiste Zeit draufgeht.
Ausserdem solltest du mal einen Blick auf das VirtualListView-Projekt im examples-Verzeichnis werfen.

ala

//Einlesen der Systemicons in das ImageListFileSymbols
	SHFILEINFO SHFileInfo;

	//kleine Symbole
	DWORD ImageHandle = SHGetFileInfo("", 0, &SHFileInfo, sizeof(SHFileInfo), SHGFI_SMALLICON|SHGFI_SHELLICONSIZE|SHGFI_SYSICONINDEX);
	if (ImageHandle != 0)
	{
		m_ImageList->Handle = ImageHandle;
		m_ImageList->ShareImages = true;
	}

	//grosse Symbole
	DWORD ImageHandle32 = SHGetFileInfo("", 0, &SHFileInfo, sizeof(SHFileInfo), SHGFI_ICON|SHGFI_SHELLICONSIZE|SHGFI_SYSICONINDEX);
	if (ImageHandle32 != 0)
	{
		m_ImageList32->Handle = ImageHandle32;
		m_ImageList32->ShareImages = true;
	}

und dann drauf verweisst mittels

AnsiString File = item.Path + "\\" + sr.Name;
				DWORD result = SHGetFileInfo(File.c_str(),
											0,
											&info,
											sizeof(info),
											SHGFI_ICON |
											SHGFI_SMALLICON);
				if (result != 0) Subfolder->ImageIndex= info.iIcon;