Apple Newton Utilities Guía de usuario descargar pdf (Pagina 760)

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CHAPTER 21

Routing Interface

21-12 Using Routing

If your application does not have a lastFormats slot, or if a matching format

is not found (the format was unregistered), the ﬁrst format found becomes the

current format.

It is your responsibility to save the

lastFormats frame to a soup if you want to

maintain it, since this information is cleared on a system reset or if your application

is uninstalled.

Supplying the Target Object 21

Next, the Routing interface sends the SetupItem message to the current format.

This message informs the format that it is selected and an item is being routed. The

SetupItem method is passed two parameters: a partially initialized item frame,

and a target information frame, as returned by

GetTargetInfo. The item frame

is obtained from the transport method

NewItem, which creates a new Out Box

item frame containing some default slots and values. This is the frame that is to be

stored in the Out Box. It must be ﬁlled in with the data object being sent.

The target information frame contains two important slots,

target and

targetView, which define the data object to be routed and the view that contains

it, respectively. The

SetupItem method must set the body slot of the item frame

to the value contained in the

target slot of the target information frame. This ﬁlls

in the item frame with the actual data to be sent.

You are not required to provide a

SetupItem method in routing formats since this

method is deﬁned in the routing format protos. The

SetupItem method deﬁned in

the protos simply assigns the

target slot in the target information frame to the

body slot of the item frame. You can override this method if you want to perform

additional operations and still call the inherited

SetupItem method. Note that

there’s a potential problem with not copying the target object. If the object is

viewable and editable and the user edits the object in the Out Box, that potentially

changes the original object stored by the application, since there are potentially not

two separate objects, but two pointers to the same object.

If you want to modify the

body slot of the item in some way, you should supply

your own

SetupItem method instead of calling the inherited version. Then

in your own

SetupItem method, clone the target slot of the target information

frame into the

body slot of the item frame.

When sending data to another Newton device (for example, by beaming) it’s a

good idea to ensure that the sent object contains a

version slot (inside the

item.body frame) that holds the current version of your application. This will help

to reduce compatibility problems in future versions of your application. If the data

format changes, your application can easily identify older and newer data formats.

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