Customizing what files you can preview is cool, but is there a way to create a custom preview extension to add syntax highlighting? I have many .h, .c, .cpp, .cs and .java files on my windows machine and it would be nice to have the syntax highlighting available via explorer's new preview pane.
6 Answers
I know the question is old. But just as other can benefit from my search I just found out a good preview handler.
https://github.com/RRUZ/delphi-preview-handler
It handles many types like c,c++,c#,.asm, and others. Plus it has support for themes.
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Just found this that supports the formats below:
http://www.smartftp.com/client/addons/sourcepreview
ActionScript (.as, .mx)
ASP (.asp)
ASPX (.aspx)
AutoIt (.au3)
Bash (.sh, .bsh)
Batch (.bat, .cmd)
Caml (.ml, .mli, .sml, .thy)
C (.c)
C++ (.cpp, .cxx, ,.cc, .h, .hxx, .rgs)
C# (.cs)
CSS (.css)
Diff (.diff, .patch)
Fortran (.f, .for, .f90, .f95, .f2k)
Ini (.ini, .inf, .reg, .url)
Inno Setup (.iss)
Java (.java)
JavaScript (.js)
Lisp (.lsp, .lisp)
Makefile (.mak)
Matlab (.m)
NFO (.nfo)
NSIS (.nsi, .nsh)
Pascal (.pas, .inc)
Perl (.pl, .pm, .plx)
PHP (.php, .php3, .phtml)
Python (.py, .pyw)
Resource (.rc)
Smalltalk (.st)
TeX (.tex)
SQL (.sql)
VB (.vb)
VBScript (.vbs)
XML (.xml, .xsd, .xsml, xsl, .kml)
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There is a Code Preview Handler, but it supports only the extensions .cs, .vb, .js and .sql . The source code is available and it doesn't look too complex to create a Preview Handler (well, sort of, I wouldn't know how to do one).
I tried adding other extensions to the Code Preview Handler with the tool Preview Handler Editor but it doesn't work, the preview pane is blank (at least for the .pl files I tried).

Edit: you have also a pack of Preview Handlers here, that support the following filetypes:
* ActionScript (.as)
* ASPX (.aspx)
* C# (.cs)
* CSS (.css)
* Diff (.diff, .patch)
* DOS (.bat, .cmd)
* JavaScript (.js)
* Ruby (.rb, .rhtml, .rjs) thanks to Ivan Porto Carrero
* SQL (.sql)
* VB (.vb)
There's an extension that supports many common coding formats here: http://blog.tatham.oddie.com.au/2006/12/20/vista-and-office-2007-preview-handler-pack-released/
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This msdn article is available as well. There seems to be enough info there to do anything we've discussed here.
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Currently it is not available and there is no add-on I can find anywhere. It has been discussed and commented about so no doubt there is demand for it. I expect an extension to come out soon.