Apple Newton Utilities Guide de l'utilisateur télécharger pdf (Page 801)

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101

CHAPTER 22

Transport Interface

Using the Transport Interface 22-13

// SendRequest method

func (newRequest)

begin

if status <> 'idle then // check if I’m active

// wait for idle and then call SendRequest again

:QueueRequest('SendRequest, newRequest);

else

// do a normal send here

end,

Canceling an Operation 22

The system sends the CancelRequest message to the transport when the user

cancels the current transaction or for other reasons, such as when the system wants

to turn off. This method must be deﬁned by all transports.

When a transport receives this message, it must terminate the communication

operation as soon as possible.

The

CancelRequest method should return non-nil if it is OK to turn off power

immediately after this method returns, or

nil if it is not OK to turn off power

immediately. In the latter case, the system waits until your transport returns to the

idle state before turning off. This allows you to send an asynchronous cancel

request to your communication endpoint, for example, and still return immediately

from the

CancelRequest method. When you receive the callback message from

your endpoint cancel request conﬁrming cancellation, use the

SetStatusDialog

method to set the transport status to idle to alert the system that it is OK to turn off.

Obtaining an Item Frame 22

The system sends the NewItem message to the transport to obtain a new item

frame to make a new In/Out Box entry.

This method is supplied by the

protoTransport, but should be overridden by

your transport to ﬁll in extra values your transport uses. If you override this

method, you must ﬁrst call the inherited

NewItem method, as shown in the

example below. The item frame returned by the

NewItem method should contain

default values for your transport.

The item frame returned by the default method supplied in

protoTransport is

not yet a soup entry. The

item.category slot is initialized to the appSymbol

slot in your transport. For more information on the

item frame, see the section

“Item Frame” beginning on page 22-2.

The

NewItem message is sent to your transport during both send and receive

operations. When the user sends an item, the system sends the

NewItem message

to the transport to create a new In/Out Box entry before opening a routing slip

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Apple Newton Utilities Guide de l'utilisateur Page 801

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