Apple Newton Utilities Guia do Utilizador descarregar pdf (Página 495)

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CHAPTER 11

Data Storage and Retrieval

Using Newton Data Storage Objects 11-63

In contrast, the EntryUndoChanges function clears the entry cache without writing

the cached entry to the soup. This function makes references to the entry point to

the original, unmodiﬁed entry residing in the soup, instead of the cached entry.

Note that reading, printing, or modifying any slot in the entry after calling

EntryFlushXmit, EntryUndoChanges, or AddFlushedXmit causes the

entire entry to be read back into the NewtonScript heap; thus, use these functions

only when you’re sure you won’t need to access the entry in the near future.

If you do need to work with the entry data after you’ve written it to the soup, you’ll

want to use functions and methods that don’t clear the entry cache after writing the

soup entry. The

AddToDefaultStoreXmit and AddToStoreXmit union soup

methods save frames as soup entries without clearing the entry cache afterward.

When adding frames to single soups, you can use the

AddXmit soup method for

the same purpose. The

EntryChangeXmit function also writes the cached entry

back to its soup without ﬂushing the cache afterward. Contrast this function with

the

EntryFlushXmit function, which clears the entry cache after writing the

cached entry back to its soup. Table 11-1 summarizes the caching behavior of all

methods that write entries to soups or union soups.

Using Soup Change Notiﬁcation 11

When your application changes an entry in a shared soup, the system executes

callback functions registered by applications using that soup, allowing them to take

action in response to the change. The system-supplied soup change notiﬁcation

service allows applications to

■ notify each other when they make changes to soup entries

■ respond to notiﬁcations precisely

Table 11-1 Effect of functions and methods on entry cache

Function or method Cached entry

uSoup:AddToDefaultStoreXmit(frame, changeSym) Creates and returns

uSoup:AddToStoreXmit(frame, changeSym) Creates and returns

soup:AddXmit(frame, changeSym) Creates and returns

soup:AddFlushedXmit(frame, changeSym) Does not create or return

EntryFlushXmit(entry) Returns existing

EntryChangeXmit(entry) Returns existing

EntryUndoChanges(entry) Throws away existing

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