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73 lines
3.7 KiB
Plaintext
73 lines
3.7 KiB
Plaintext
ABOUT THE CODE
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--------------
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WHAT HAPPENS WHEN A TEMPLATE EDITOR IS OPENED FOR A RESOURCE
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The template editor uses a dedicated class for each field type (or family of field types).
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These classes are all subclasses of the common base class NuTemplateElement. For things like
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lists, there is a subclass NuTemplateGroupElement from which you can instead subclass to
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have some of the work done for you.
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When opening a resource, the template editor first creates a NuTemplateStream for the template
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resource and calls readOneObject: on it until it runs out of data, instantiating a hierarchy
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of NuTemplateElement subclasses for based on the template.
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After that, it creates a NuTemplateStream for the resource and loops over the template object
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hierarchy, creating a copy of each item, and then calling readDataFrom:containingArray: on
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the copy, which in turn reads data from the NuTemplateStream and stores it in its instance
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variables. For this to work, subclasses of NuTemplateElement *must* implement the NSCopying
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protocol.
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This results in an object hierarchy that describes the entire resource using template fields
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containing the data, which can now be edited, displayed in lists, etc.
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WHAT HAPPENS WHEN THE TEMPLATE EDITOR IS CLOSED
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As soon as the template editor is closed, another NuTemplateStream is created for the
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resource and passed to all template fields (the copies with the resource data, not the
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pre-parsed template hierarchy), via writeDataTo:, which is where they should write their
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data to the stream. Before that, sizeOnDisk is called on each NuTemplateElement to
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calculate the new size of the resource before the actual process of writing them out.
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This size must include the size of all of their sub-items, and writeDataTo: must call
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these sub items if they are to be written to disk.
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SPECIAL CASE: LISTS
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When the editor encounters an LSTB element, the LSTB element is called upon to parse its
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"sub-elements" (the items that make up one list item). The LSTB element reads all elements
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from the template, up to the terminating LSTE element, and keeps the array of parsed
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sub-elements around in one of its data member variables. Parsing then resumes after the
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"LSTE" element.
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When the LSTB element is later called upon to read its data from the resource displayed in
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the template, it will loop over its list of sub-elements and will generate a copy of itself
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and all sub-elements except the "LSTE" for each list item. After all items have been read,
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a single copy of the "LSTE" element is added at the end of the list. If the list is empty,
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the "LSTB" will simply create an "LSTE" element and delete itself.
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The "LSTE" element contains a copy of the sub-elements list of the LSTB, but doesn't read
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any data from the resource. When either an "LSTE" or "LSTB" element are selected, the user
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can choose "New List Item..." from the "Resource" menu to create a copy of the selected
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element's sub-elements, along with an "LSTB" element containing them. Thus, the user can
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create new items before any existing item (i.e. "LSTB" element), as well as at the end of
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the list or when the list is empty, by selecting the "LSTE". "LSTB" items can also be
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deleted using the "Edit" menu.
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In short:
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-> New list items are created by copying an existing "LSTB" and all its sub-elementss.
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-> A single "LSTE" element serves as an "end marker" for full and as a placeholder for
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empty lists, and can also be used to create new "LSTB"s with sub-elements.
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Analogous behaviour is employed for other kinds of lists, except that additional
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features in LSTEs are activated to allow writing terminating zeroes to the file, and
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that the equivalent to the "LSTB" item may also update a counter field.
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REVISIONS:
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2003-08-13 UK Finished chapter on lists, added revision history.
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2003-08-08 UK Created.
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