Apple Newton Internet Enabler Especificações descarregar pdf (Página 4)

June 1996 Newton Technology Journal

Then, when you call the InetGrabLink function in your application,

you pass it the name (symbol) of your callback function. For example:

myApp.TestGrab := func()

begin

myStatusView := InetStatusDisplay(nil, nil, nil);

InetGrabLink(nil, self, 'GrabLinkCallback);

...

end;

This function first calls the InetStatusDisplay function to

create and display the status view. The call to InetGrabLink uses the

default link ID and specifies self (the application frame) as the value of the

clientContext

parameter, and 'GrabLinkCallback (the symbol

for the callback function) as the value of the

clientCallback

parameter.

The GrabLinkCallback function will be called repeatedly while the

system is attempting to grab the link, until either the status is

'connected or an error occurs.

USING THE LINK CONTROLLER INTERFACE

You can use the Link Controller to create and manage a link between a

Newton device and the Internet. The Link Controller can manage a single

link for multiple applications simultaneously. This means that one

application establishes the link and other applications use the same link.

To establish (grab) a link, you call the InetGrabLink function. The

first grab of a link can be expensive in terms of time: typically, the Inet tool

software dials the Newton modem and negotiates the connection to establish

an Internet session. The Inet tool then performs whatever login and

initialization procedures are required, which the user has configured with the

Internet Setup application. All of this can take a substantial amount of time.

Since it can take so much time to grab a new link, Newton Internet

Enabler makes it easy for another application to grab a link that has already

been established by maintaining a reference count of users for each link.

Whenever an application grabs a link, the link controller increments its count

of users of that link. The physical link is dropped only after all users have

released the link (when the count becomes 0).

Most of the link controller functions operate asynchronously. After the

Inet tool initiates the operation, it returns control to your application. When

the operation is complete, or in some cases while the operation is in

progress, the Inet tool notifies you by calling a callback function that you

have provided. You can use your callback functions to monitor the status of

a link and to determine if an operation was successful or not.

While the grab of a link is in progress, the Inet frequently calls your

callback function, providing it with information about the current status of

the link. You can send this status information along to the

InetStatusDisplay function to provide visual feedback to the user

about the connection process.

The following is an example of a typical flow of operations that occur

during an Internet session using Newton Internet Enabler:

1. An application (My_Application) issues a call to the InetGrabLink

function. The link controller dials the modem and begins an Internet

session with an Internet provider.

2. While the grab operation is in process, the Inet tool periodically calls the

callback function that My_Application has defined for grab operations.

This callback function calls the InetStatusDisplay function to

update the on-screen display of the current status of the link.

3. When the grab operation completes, the callback function removes the

status display from the screen.

4. My_Application instantiates and binds one or more endpoints to use

over that link. Each endpoint can use either the TCP or UDP transport

services, and each endpoint can be bound either to initiate an outgoing

connection (connect) or to listen for an incoming connection (listen).

5. My_Application uses its endpoint(s) to perform communications

operations, calling endpoint methods such as Output and

SetInputSpec.

6. Another application (Your_Application) issues a call to the

InetGrabLink function to use the same service provider as

My_Application. The Inet tool returns the same link that it established

in step 1.

7. Your_Application creates and uses endpoint(s) to perform

communications operations.

8. Your_Application finishes its use of the link and calls the

InetReleaseLink function. The link controller decrements its

count of users of the link.

9. A third application (Their_Application) grabs the link, creates endpoints

to use over the link, and releases the link.

10. My_Application finishes its use of the link and calls the

InetReleaseLink function. The link controller decrements its

count of link users. The count becomes 0, so the link is dropped: the

Internet session ends, the modem is hung up, and any resources used

for the link are released.

Grabbing a Link

To get started, you need to establish (grab) a link. To establish a link, you

need to call the InetGrabLink function. You need to provide

InetGrabLink with a link ID, a callback function, and a callback

context frame:

InetGrabLink(linkID, clientContext, clientCallback)

For the link ID, you can tell InetGrabLink to use the default link by

using nil or you can use an identifier returned by the

InetAddNewLinkEntry function as the value of this parameter.

When you specify nil, the system software uses the link ID that has been

established as the default link ID, which is almost always what you want to do.

The InetGrabLink operation can take some time to complete. While

it is in progress, the Inet tool repeatedly calls your callback function to report the

current status of grabbing the link. The Inet tool calls your callback function until

either an error occurs or until the status becomes 'connected.

The status value in your callback is a status frame. This frame contains

the current link status value and (possibly) other information. In your

callback, you can use the InetDisplayStatus function to show the

current status to the user. The next section, “Retrieving and Displaying Link

Status Information,” describes how to display status to the user.

Here is an example of a callback function for the InetGrabLink

function:

myApp.GrabLinkCallback := func(linkID, stat, err)

begin

myLinkID := linkID; // save the link ID

// during grab processing, display status & return

if err = nil and status.linkStatus <> 'connected then

return InetDisplayStatus(linkID, myStatView, stat);

// at this point, either we are connected or we

// got an error, so close the status display

InetDisplayStatus(linkID, myStatView, nil);

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