Apple Newton Utilities Guia do Utilizador descarregar pdf (Página 634)

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CHAPTER 17

Additional System Services

17-18 Using Additional System Services

The code above shows the two ways in which your code can respond when the user

cancels the operation. If the user taps the Stop button an exception is thrown by

SetStatus. You may catch this exception and perform any clean-up necessary.

(In the code above the all-inclusive

|evt.ex| onexception clause catches this

exception.) You must, however, rethrow this exception so the system can perform

its own cleanup, otherwise the Newton device appears to hang. You must ensure

that any exceptions you do not speciﬁcally anticipate are rethrown by your

exception-handling code.

You may also perform any necessary housecleaning after an uncompleted operation

by comparing the result of the

DoProgress function. If the user tapped the Stop

button,

DoProgress returns the symbol 'cancelled.

Using DoProgress or Creating Your Own protoStatusTemplate 17

The DoProgress function creates a view based on the protoStatusTemplate

to report progress to the user. Using this function is the simplest way to create a

protoStatusTemplate view. However, it is not suitable for all applications.

You should use

DoProgress if

■ Your code is structured synchronously; that is, DoProgress does not return

until the workFunc function has completed or the user cancels the operation.

■ The built-in bar gauge or barber pole status slips which DoProgress uses are

suitable for your needs.

■ The action is modal; that is, the user cannot do anything until the action ﬁnishes

or is canceled.

If any of these is not true, use

protoStatusTemplate; that is you should create

your own

protoStatusTemplate if

■ Your code is structured asynchronously; that is, it allows user events to be

processed normally.

■ Your code uses communications; these usually have asynchronous components.

■ Your code requires a custom status template type; possibly for a transport.

■ Your actions are not modal; that is, the user could proceed in your application or

other applications while the action is in progress.

Using protoStatusTemplate Views 17

You need to take the following steps to use a protoStatusTemplate view to

report progress to the user:

1. Specify the components of the status slip and their initial values. You can use

one of the system-supplied templates or create your own template.

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