Apple Newton Utilities User's Guide download pdf (Page 798)

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CHAPTER 22

Transport Interface

22-10 Using the Transport Interface

Some transports may ignore the ReceiveRequest message, since they receive

data continuously. Others may use this message as a trigger to initiate a connection.

You can choose to comply with or ignore any request to receive, depending on the

communication resources available and their status. If you choose to comply, the

ReceiveRequest method should establish a connection and begin receiving by

whatever means the transport uses to communicate. For example, many transports

use the Endpoint interface to establish and operate a connection. After receiving the

item, you should call the transport method

NewFromItem to copy it into a

standard item frame used by the In/Out Box. Finally, you must call

ItemCompleted to write the item to the In Box.

If your transport creates virtual binary objects, you must use the method

GetDefaultOwnerStore to determine on which store to create them.

Note

The body slot within every received item must have a class slot

to identify its data class. Data objects received from other Newton

devices always have a

class slot. For data received from other

systems, your transport must assign a meaningful class to the

item.body object. ◆

Deferring Reception of the Item Data 22

Some transports might want to download just part of an item initially, such as its

title, then download the actual item data when a user requests it. For example, upon

connection an e-mail transport might download just the titles of messages or other

data objects. When the user attempts to view one of these items in the In Box, the

transport then downloads the body of the item from the remote host.

This feature is accomplished by the use of the

cause slot in the parameter passed

to the

ReceiveRequest method, and by the use of a remote slot in the item frame.

If a transport initially downloads just a part of each item, such as its title, it must

insert a slot called

remote, whose value is true in the item frame of those items.

This slot serves as a ﬂag to tell the In/Out Box that the body of the item is stored

remotely and has not yet been downloaded.

When the user attempts to view one of these items in the In Box, the In Box sees

the

remote slot, and sends the transport the ReceiveRequest message with the

'remote cause. This alerts the transport to download the body of the item from

the remote host. If the user selected multiple remote items for downloading, you

must use the

ItemRequest method to retrieve subsequent requested items and

download them. Keep calling

ItemRequest until it returns nil, which signals

that there are no more items to retrieve.

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Apple Newton Utilities User's Guide Page 798

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