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VB Shell Programming
book

VB Shell Programming

by J.P. Hamilton
July 2000
Intermediate to advanced
392 pages
10h 19m
English
O'Reilly Media, Inc.
Content preview from VB Shell Programming

Chapter 5. Icon Handlers

Icons are defined for a particular file class by adding a DefaultIcon key under the files association key in the registry. DefaultIcon is then set to a path containing the .exe or .dll that contains the icon to be displayed and the zero-based index of that icon within the file, if multiple icons are present. Figure 5.1, for example, shows the relevant registry keys for our example .rad file type, which is configured to use the second icon in notepad.exe. Every icon for the file class in question will have the same icon when this key is registered.

Registering the default icon for a file class

Figure 5-1. Registering the default icon for a file class

Icon handlers allow file objects of the same type to display different icons on a per-instance basis. This means that such things as the value of particular file attributes or state information internal to the file can be conveyed to the user through the shell. Take the .rad file, for instance. Using an icon handler, we could display a picture of the animal represented by the file (for a limited number of animals, of course), the age of the animal, the gender, or whatever.

How Icon Handlers Work

Icon handlers are required to implement two interfaces: IPersistFile and IExtractIcon. These interfaces are interesting from a programmatic standpoint for several reasons. IPersistFile is not directly derived from IUnknown; it’s derived from IPersist. And as luck ...

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Publisher Resources

ISBN: 1565926706Catalog PageErrata