Class: Notification

• Inheritance
• Description
• Related information
• Class protocol
  • answering queries
  • initialization
  • misc ui support
  • queries
• Instance protocol
  • default actions
  • private
  • queries
  • testing
• Examples

Inheritance:

   Object
   |
   +--GenericException
      |
      +--Notification
         |
         +--ClassDescription::PackageRedefinition
         |
         +--Dolphin::Notification
         |
         +--EndOfStreamNotification
         |
         +--HTTPInterface::TransferProgressNotificationSignal
         |
         +--HTTPInterface::TransferTimeoutNotificationSignal
         |
         +--HTTPRequest::ReprocessRequest
         |
         +--HTTPServer::TerminationRequest
         |
         +--IncrementNotification
         |
         +--ObjectFileLoader::ObjectFileLoadErrorNotification
         |
         +--Parser::ParseWarning
         |
         +--Parser::UndefinedVariableNotification
         |
         +--Query
         |
         +--RecursiveStoreError
         |
         +--SimpleView::AboutToOpenBoxNotificationSignal
         |
         +--UserNotification
         |
         +--YesToAllConfirmation

Package:

stx:libbasic

Category:

Kernel-Exceptions

Version:

rev: 1.25 date: 2009/10/14 17:34:24

user: cg

file: Notification.st directory: libbasic

module: stx stc-classLibrary: libbasic

Author:

Stefan Vogel

Description:

Notification is the superclass of all notification signals in the system.
contrast to regular exceptions, Notifications are ignored, if no handler is present
and a default value is returned from the raise.
When a handler finishes, the do-block is proceeded with the exception handlers value
(an Exception does a return in this case.).

Thanks to proceedable exceptions, Notifications allow for non-GUI model code to provide
user notifications which are optionally shown.
Very useful, for example to provide progress information from a method which can be
invoked both from a GUI-Tool (where notifications are wanted) and also from the system,
where such notifications are not desired.

Related information:

    Signal
    QuerySignal

Class protocol:

 answer: someAnswer do: aBlock

evaluate the argument, aBlock.
If the receiver is queried during evaluation, answer and proceed with someAnswer.
This is a wrapper for #handle:do: for lazy typists; no new functionality.

 initialize

 iconInBrowserSymbol

 accepts: aSignal

return true, if the receiver accepts the argument, aSignal.
(i.e. the receiver is aSignal or a parent of it). False otherwise.

 defaultAnswer

Return the default answer to the Query. This method is called,
if nobody catches the signal.

Subclasses may redefine this method.

 handlerForSignal: signal context: theContext originator: originator

answer the handler block for the signal from originator.
The block is retrieved from aContext.
Answer nil if the signal is not handled

 handles: anException

return true, if the receiver handles the argument, anException.
(i.e. the receiver is anExceptions signal or a parent of it)

 isQuerySignal

return true, if this is a querySignal - always return true here

 notify: aMessageString

raise the query - return the handlers value, or the default
value, if there is no handler.

 query

raise the query - return the handlers value, or the default
value, if there is no handler.
Invoking the handler is exactly the functionality of Signal>>raiseRequest,
but we can do it faster here (avoiding the construction of an exception instance).

 raise

QuerySignals are proceedable by definition,
so they should be raised with #query or #raiseRequest

 raiseRequest

redefined to use #query

Instance protocol:

 defaultAction

the default action is to return the default value.
Subclasses may redefine this

 LATERdoCallHandler: aHandlerBlock

SV: Have to think about...

 query

notice the implementation on the class-side: if no additional parameters are to be passed,
we do not even arrive here, because query has inlined the raiseRequest code

 isNotification

Examples:

  |zero|

  zero := 0.
  Notification handle:[:n |
      Transcript showCR:'Please note that: ' , n description.
      n proceedWith:true
  ] do:[
      'nesting'.
      [
          [
              Error handle:[:ex |
                  Transcript showCR:'some error: ' , ex errorString.
                  ex proceed
              ] do:[
                  [
                      1 // zero.  'an error which is caught in the handler'.
                      Notification notify:'hello world'
                  ] value
              ]
          ] value
      ] value
  ]