said:
>The "Become" tab in the Properties notebook appears when a data file has
>extended attributes, and does not appear on files which have zero-length
>extended attributes.
Yep, it's got to have a .CLASSINFO EA to be a class object.
>And, the "Become" tab's Help button says it is for changing an object's
>Workplace Shell "Class". The "Become" tab allows you to choose a
>different "class handler" to manage the "object" (the file).
And notice that there's a limited set of "Become" options. Probably
related to the class hierarchy.
> 1. What is the "class handler" referred to by the above-mentioned Help
>button? Is it some code that executes in the Workplace Shell?
It's a computer. It runs code, so the answer must be yes :). Every class
has a associated DLL registered with the WPS. There's a REXX command to
list them. The DLL's talk to the WPS class DLL's and other classes via
SOM which is an implementation of a CORBA interface.
> 2. How do you set a file's Workplace Shell "Class" if it doesn't have
>one already (or if it has one and you want to change it)? For example,
>the RexxUtil SysCreateObject function may do this, but I'm not sure of
>the syntax. And how do you do this in C?
Dunno for sure. You've probably got to talk to the WPS. There's a ton of
wp...() functions to do this. It will take a bit of work to find the
specific one. It could be the equivalent of SysSetObjectData, but I don't
know.
> 3. What is the purpose of the Workplace Shell "Class"? What uses it?
>What is it used for? Are there programs that check this tag before
>opening the file to see how it should be processed? Does the Workplace
>Shell check this tag when you click on a data file object to decide how
>to handle it?
It's object oriented and sorta the other way around. The class is a
"smart pointer" to all the functions that perform actions on an object.
When you double click on an object icon, PMSHELL's message handler (I
think) detects the click and "OK so you want to open this" and converts
the icon location to an object handle (by magic) and invokes the "Open
Method" associated with the class. The Open Method is invoked and passed
a handle to the object. What the Open Method does is implementation
specific. In the case of folders the folder will open in the default
view. In the case of a Mesa spreadsheet, the class handler will invoke
Mesa.exe and pass it the name of the sheet to be open. Some of this
linkage is guess-work on my part an may need to be corrected by other that
really know.
Steven
--
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Steven Levine MR2/ICE #10183
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