Preview Handler

The Bentley DGN Preview Handler allows you to see the contents of a DGN file without opening the file inside an application. You can view all types of DGN files (DGN, I.DGN, and OVERLAY.DGN) in Microsoft Windows 10, Microsoft Windows 8, Microsoft Windows 7, and Microsoft Outlook. Prevhost.exe is a file associated with Preview Handlers, and is safe to run on your PC. Microsoft Windows is a range of graphical operating system families developed by Microsoft. First released 32 years ago, it once had an over 90 percent market share in the personal computer segment, and today is available in 133 different languages. Windows and Office Preview Handler Pack is one such custom previewers or preview handlers that provides support for.cs,.aspx and.sql source codes. With the handler pack installed, you can just click on the file ending with extension of.cs,.aspx and.sql with preview pane on, and instantly view the file content in the preview pane.

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This topic explains how to register a preview handler associated with a given data type. For the purposes of illustration, examples in this topic use a .xyz file type. Registration of a preview handler is a standard file association-based registration.

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Instructions

Preview Handlers

Step 1:

First, a file name extension is associated with a ProgID. The following entry associates the xyzfile ProgID subkey with the .xyz file name extension.

The xyzfile ProgID subkey is stored with the other ProgIDs as shown here:

Each preview handler ProgID subkey contains a subkey named shellex that contains a subkey always named {8895b1c6-b41f-4c1c-a562-0d564250836f}. The presence of that subkey tells the system that the handler is a preview handler. Can't deliver documents to my kindle for mac reader windows 10.

The default value of the {8895b1c6-b41f-4c1c-a562-0d564250836f} subkey is the class identifier (CLSID) of your handler. An example of the xyzfile ProgID subkey is shown here, associating a handler of CLSID {ec3a629a-a47c-4245-bc78-b4b63d0e3154}.

Step 2:

Next, add the subkey under CLSID for your preview handler. An example is shown here. An explanation of individual entries follows.

The default value for your subkey (here, {ec3a629a-a47c-4245-bc78-b4b63d0e3154}) is not required or used. However, setting it to a nonlocalized string can help you to debug registration issues.

The minus sign (-101) in the .dll resource in the DisplayName entry exists for legacy reasons. The Icon entry, on the other hand, does not require a minus sign.

The AppID value gives a reference to the AppID of the application associated with the file name extension (stored under HKEY_CLASSES_ROOTAPPID. The value used here—{6d2b5079-2f0b-48dd-ab7f-97cec514d30b}—is the ID of the Prevhost.exe surrogate host. 32-bit preview handlers should use AppID {534A1E02-D58F-44f0-B58B-36CBED287C7C} when installed on 64-bit operating systems.

The entries under the InprocServer32 subkey include a reference back to the file name extension's ProgID subkey as well as an entry for a VersionIndependentProgID.

Step 3:

Finally, the preview handler must be added to the list of all preview handlers. This list is used as an optimization by the system to enumerate all registered preview handlers for display purposes. Again, the default value is not required, it simply aids in the debugging process.

Note

In Windows 7, if the application is installed for all users of the computer, use HKEY_LOCAL_MACHINE; if for only one user, use HKEY_CURRENT_USER.

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