The Registry RevealedThe Registry Revealed

Shell Key Structures (continued)
In each case, a ContextMenuHandlers subkey specifies these unique context menu options. This key may also contain its own subkeys, such as the IconHandler subkey found under the Lnkfile, Piffile and a few other keys, where it does what you'd expect. For example, use Explorer to search the C:\WINDOWS folder and its subdirectories for *.LNK or *.PIF files. Open the context menu for any such file and select Properties, and IconHandler should place its icon near the top of the General tab. If the IconHandler subkey were missing, a generic document shortcut icon would appear there instead.PropertySheetHandlers. The subkey beneath any key with this name serves as a pointer to a CLSID key. The PropertySheetHandlers key sometimes supports a single property sheet, as in the case of the AVIFile key. Here, the Contents pane for the PropertySheetHandlers key shows "AviPage" in its Data column. A subkey with that name appears below it, and AviPage's Contents pane points to the CLSID key associated with the AVI file. In the Contents pane of that key's InProcServer32 subkey, you'll find the following information:

(Default) "C:/WINDOWS/SYSTEM/mmsys.cpl"

This indicates the MMSYS.CPL file contains the Property sheet information required by AVI files. If that file is missing, the Details and Preview tabs on an AVI file's Properties sheet will also be missing.

The ShellNew Key. If you select the Desktop context menu's New option, a cascading menu displays a list of new options. You'll find a ShellNew key under the file extension subkey associated with each option's document type. For instance, the Contents pane for the HKCR/.bmp subkey points to a Paint.Picture subkey. The Contents pane for that key lists the text that appears on the cascading New menu (Bitmap Image), and the Shell/open/command subkey specifies the executable file that will launch to create the appropriate new document on the Desktop.

The ShellNew key's role varies depending on the information in its Contents pane. To illustrate this, open the ShellNew subkey under any file extension key, note the word that appears on the second line in the Contents pane, then find that word in the list that follows. In each of the following examples, the Data column's contents determine the action taken:

Command. The Data column specifies a command line that executes if you select the related option on the New menu. The command line specifies the path, filename and command line parameters needed to create the specified new item.

Data. If a binary data string appears in the Data column, that string is written into a new file of the appropriate format. For instance, a multimedia application may write a Data entry into the Contents pane in the .mid (MIDI file) key's ShellNew subkey, such as the 18-byte header that appears at the beginning of any MIDI file. If this sequence appears in the Data column, the application that wrote the Data entry supports MIDI recording. Therefore, the New MIDI Sequence.mid file in the C:\WINDOWS\DESKTOP folder should be 18 bytes long. If the .mid subkey doesn't contain a ShellNew key, no MIDI sequence option will appear on the Desktop context menu's cascading New menu.

FileName. When FileName shows in the Name column, the Data column specifies a new document file that will be placed on the Desktop, not unlike the binary header just described. However, the binary header is written as a new file; a new document file is actually a copy of a blank document file currently located in the C:\WINDOWS\SHELLNEW folder. This blank file may be quite a bit larger than the 18-byte MIDI header described above because it contains all the basic data required for any new file created under the same format.

If you subsequently double-click on the new document file's icon, the executable that loads the file is the one specified under the FileType subkey associated with the file extension key. To locate it, open any file extension key and note the FileType listed in its Contents pane. Then locate the subkey with that name, and open its Shell/Open/Command subkey. The path and filename for the executable file are located in the (Default) row's Data column.

NullFile. The Data column shows an empty pair of quotation marks, and in this case, a null file (of 0-byte length) is created on the Desktop. A Nullfile entry is found under the .bmp and other subkeys because the format of the file you want to create is unknown, so Win95 can't write the correct header into the new file. Presumably, you'll open the Nullfile, add something to it and save it in whatever format you prefer. Win95 then writes the correct header into the file.

This is just a small peek into a small corner of one of six HKEYs in the Win95 Registry. Most of it is swiped from chapter 1 of my Registry book. Nevertheless, I hope it's enough to provide a general understanding of how the Registry works.

Open HKEY_CURRENT_USER/Control Panel and highlight the Desktop subkey. The Contents pane shows the current Desktop settings, which don't yet include a MenuShowDelay line.

Open the Edit menu and select New/String Value. A New Value #1 box should appear at the bottom of the Contents pane. Overtype this with MenuShowDelay and press Enter.

Select View/Refresh to sort the items in the Contents pane. Double-click on MenuShowDelay to open the Edit String dialog box. Type 1000 (or some other millisecond value, as desired) in the Value data box. When you click on the OK button, the dialog box closes and the new value appears in the Data column.

In addition to Windows 95 Registry: A Survival Guide for Users (MIS:Press, 1996), Senior Contributing Editor John Woram is also the author of Windows Configuration Handbook (Random House, 1993).

Windows Magazine -- February 1997, page 217.
[ Go to February 1997 Table of Contents ]