Apple Newton Utilities Uživatelská příručka stáhnout pdf (Strana 807)

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CHAPTER 22

Transport Interface

Using the Transport Interface 22-19

Application Messages 22

Applications can send messages directly to a single transport or to all transports by

using the

TransportNotify global function. This mechanism serves as a

general way for applications to communicate with transports. Here is an example

of using this function:

TransportNotify('_all,'AppOpened,[appSymbol])

The In/Out Box uses this mechanism to send three different messages to transports:

AppOpened, AppClosed, and AppInFront. The AppOpened message notifies

the transport that an application has opened and is interested in data from the

transport. The In/Out Box sends this message to all transports when it opens. This

method is not deﬁned by default in

protoTransport since it’s transport-speciﬁc.

If you want to respond to the

AppOpened message, you must deﬁne this method in

your transport.

This message is designed to support applications that might poll for data, such as a

pager. For example, when the application is open, it can notify the transport with

this message so that the transport can poll more frequently (and use more power)

than when the application is closed. Another use might be for an application to

notify a transport that automatically makes a connection whenever the application

is open.

The

AppClosed message notiﬁes the transport that an application has closed. The

In/Out Box sends this message to all transports when it closes. Again, this method

is not deﬁned by default in

protoTransport since there is no default action—

it’s transport-speciﬁc. If you want to respond to the

AppClosed message, you

must deﬁne this method in your transport.

Note that more than one application can be open at a time in the system. If you

want your transport to do something like disconnect when it receives this message,

keep track of how many times it’s received the

AppOpened message and don’t

actually disconnect until it receives the same number of

AppClosed messages.

The

AppInFront message notiﬁes the transport of a change in the frontmost

status of an application—either the application is no longer frontmost, or it now is.

The In/Out Box sends this message to all transports when another application is

opened in front of the In/Out Box view, or when the In/Out Box view is brought to

the front. Note that the

AppInFront message is not sent when an application is

opened or closed, so you need to check for the

AppOpened and AppClosed

messages to catch those occurrences.

Again, this method is not deﬁned by default in

protoTransport since there is

no default action—it’s transport-speciﬁc. If you want to respond to the

AppInFront

message, you must deﬁne this method in your transport. Not that this method is

used only in special circumstances and is not needed by most transports.

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