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CHAPTER 21

Routing Interface

Using Routing 21-13

Storing an Alias to the Target Object 21

When there is a single target object, if there is not enough storage space, or the

target object is larger than a speciﬁed size, you can specify that an alias to the

target object, rather than the target object itself, be stored in the item.body slot.

This can be a soup entry alias or you can implement your own alias handling. You

enable the storing of an alias by setting the storeAlias slot in the routing format

frame to

true. Additionally, you can specify a maximum size limit for target

objects by setting the

sizeLimit slot in the routing format frame. If any target

object is larger than the size speciﬁed in this slot, and

storeAlias is also true,

an alias to the target object is stored in the

item.body slot. To store every target

as an alias, set

sizeLimit to 0.

The default

SetupItem method provided in the routing format protos reads the

storeAlias slot and performs the appropriate operations if this slot is true;

otherwise, it assigns the actual target object to the

item.body slot, as usual. If an

alias to the target object is stored in the

item.body slot, the routing interface also

sets the

item.needsResolve slot to true, to signal that the body slot contains

an alias that needs to be resolved.

When it’s time to send an item, the format ResolveBody method is used to resolve

an alias before the item is sent. The item won’t be sent until the alias is resolved

(ResolveBody returns a non-nil value), since there’s no point in sending an alias.

If an alias to an item is stored, the item can still be viewed and operated upon in the

In/Out Box, just like any other item.

Note that there are some potential problems if an alias to the target object is stored.

If the target entry resides on a card store, and the card is removed before the item is

actually sent from the Out Box, the alias cannot be resolved and the send operation

on that item will fail. No matter where the original object resides, even if it is simply

deleted, the send operation on that item will fail. Therefore, whenever an alias is

stored, the user is warned by an alert slip explaining that the original item must be

available when the routed item is actually sent. You can set the routing format slot

showMessage to nil to prevent the warning message from being displayed.

Another problem with storing an alias is that the alias is just a pointer to the

original data. For example, say the user faxes a note and chooses to send it later,

and you store an alias to the note in the Out Box. Then the user opens the fax item

in the Out Box and changes the note. This actually changes the original note in the

Notes application, since the alias is a pointer to the original soup entry. Similarly, if

the user changed the original note before the fax was sent, then the fax text would

be changed without the user being aware of it.

Most target objects are soup entries, for which the routing format protos can handle

the operations of determining the object size, making an alias, and resolving the

alias when needed. However, in some cases, you may want to route objects that are

not soup entries. If you want to create custom aliases to such objects, you must

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