Limitations with NewtOverview Data Class

One of the Newton 2.x OS Q&As
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This document was exported on 7/23/97.

Limitations with NewtOverview Data Class (1/8/97)

Q: I want to use code like CreateTargetCursor('newtOverview, myItemArray) in my application to simplify my code which handles overviews. Why would my print format throw an exception when I use this method?

A: There are limitations to using the 'newtOverview symbol as your data class with CreateTargetCursor. The biggest limitation is that it requires you to support exactly the set of of datatypes: ['frame, 'text, 'view]. In other words, you must register a protoFrameFormat (by default, it handles 'frame and 'text dataTypes) and a protoPrintFormat. However, there are two other limitations not mentioned in the final documentation: the system does not guarantee that it will call your print format's formatInitScript method or a format's SetupItem method.

This means that if your print format's viewSetupFormScript (or other code in the print format) assumed that the formatInitScript has been called, it could cause errors and/or exceptions. The workaround to this would be to set a flag in the formatInitScript; if it was not set at the beginning of viewSetupFormScript, send your format the formatInitScript message. Other problems could occur with SetupItem, but you'd probably not see any errors or exceptions until you tried to beam/mail a frame to another device and then tried to Put Away the item.

About the default overview class: when you use CreateTargetCursor to prepare a "multiple item target", you may be able to use this special 'newtOverview symbol as your data class. If your application prints every item on separate pages (in other words, not multiple items on one page) and you want to split beam and mail items into separate items in the Out Box, this might be useful to you. For more information, see the Newton Programmers Guide (not reference) in the Routing chapter "Using the Built-in Overview Data Class" section and the "Move It!" article in the Newton Technology Journal 2.02. Also, check out the MultiRoute DTS sample.