"

 COPYRIGHT (c) 1995 by Claus Gittinger

	      All Rights Reserved

 This software is furnished under a license and may be used

 only in accordance with the terms of that license and with the

 inclusion of the above copyright notice.   This software may not

 be provided or otherwise made available to, or used by, any

 other person.  No title to or ownership of the software is

 hereby transferred.

"

ValueHolder subclass:#BufferedValueHolder 

	 instanceVariableNames:'subject triggerChannel bufferedValue'

	 classVariableNames:'NotYetAssigned'

	 poolDictionaries:''

	 category:'Interface-Support-Models'

!

!BufferedValueHolder class methodsFor:'documentation'!

copyright

"

 COPYRIGHT (c) 1995 by Claus Gittinger

	      All Rights Reserved

 This software is furnished under a license and may be used

 only in accordance with the terms of that license and with the

 inclusion of the above copyright notice.   This software may not

 be provided or otherwise made available to, or used by, any

 other person.  No title to or ownership of the software is

 hereby transferred.

"

!

version

"

"

!

documentation

"

    a bufferedValueHolder keeps a temporary copy of the realHolders value,

    and only does a real store of the value when triggered.

    Triggering is done by depending on a trigger objects value, which is

    typically a ValueHolder for a boolean, which is set by an ok-button.

    Notice: this class was implemented using protocol information

    from alpha testers - it may not be complete or compatible to

    the corresponding ST-80 class. If you encounter any incompatibilities,

    please forward a note to the ST/X team.

"

!

examples 

"

    unbuffered (values are changed, even if not accepted,

    iff a field is left with Return or accept is done in a field):

	|firstName lastName dialog|

	firstName :=  'foo' asValue.

	lastName := 'bar' asValue.

	dialog := Dialog new.

	(dialog addTextLabel:'Name:') layout:#left.

	dialog addInputFieldOn:firstName.

	dialog addVerticalSpace.

	(dialog addTextLabel:'Address:') layout:#left.

	dialog addInputFieldOn:lastName.

	dialog addAbortButton; addOkButton.

	dialog open.

	Transcript show:firstName value; show:' '; showCr:lastName value

    buffered (values are only stored when accepted; undo reloads old values)

    (use an instance of TriggerValue. If a ValueHolder was used, we had

     to temporarily set its value back to nil, to have the change really be

     forwarded to its dependends)

	|firstName lastName trigger dialog|

	firstName :=  'foo' asValue.

	lastName := 'bar' asValue.

	trigger := TriggerValue new.

	dialog := Dialog new.

	(dialog addTextLabel:'Name:') layout:#left.

	dialog addInputFieldOn:(BufferedValueHolder

				    subject:firstName

				    triggerChannel:trigger).

	dialog addVerticalSpace.

	(dialog addTextLabel:'Address:') layout:#left.

	dialog addInputFieldOn:(BufferedValueHolder

				    subject:lastName

				    triggerChannel:trigger).

	dialog addAbortButton; 

	       addButton:(Button new 

				label:'undo'; 

				action:[trigger value:false]);

	       addOkButton.

	dialog open.

	dialog accepted ifTrue:[

	    trigger value:true

	].

	Transcript show:firstName value; show:' '; showCr:lastName value

"

! !

!BufferedValueHolder class methodsFor:'initialization'!

intialize

    NotYetAssigned := Object new

! !

!BufferedValueHolder class methodsFor:'instance creation'!

subject:someModel triggerChannel:aTrigger

    "return a new BufferedValueHolder offering a buffered copy of someModels

     value - only updating this value, when aTrigger changes to true."

    ^ self new subject:someModel; triggerChannel:aTrigger

! !

!BufferedValueHolder methodsFor:'initialization'!

initialize

    super initialize.

    bufferedValue := NotYetAssigned

! !

!BufferedValueHolder methodsFor:'change & update'!

update:something with:aParameter from:changedObject

    changedObject == triggerChannel ifTrue:[

	triggerChannel value == true ifTrue:[

	    "

	     now, store the buffered value into the subject

	    "

	    subject value:bufferedValue.

	    ^ self

	].

	triggerChannel value == false ifTrue:[

	    "

	     cancel: flush my buffered value

	    "

	    bufferedValue := NotYetAssigned.

	].

	self notifyChange:#value. 

	^ self

    ].

    changedObject == subject ifTrue:[

	bufferedValue := NotYetAssigned.

	self notifyChange:#value.

	^ self

    ].

! !

!BufferedValueHolder methodsFor:'accessing'!

subject:someModel

    subject notNil ifTrue:[

	subject removeDependent:self

    ].

    subject := someModel.

    subject notNil ifTrue:[

	subject addDependent:self

    ]

!

triggerChannel:aTrigger

    triggerChannel notNil ifTrue:[

	triggerChannel removeDependent:self

    ].

    triggerChannel := aTrigger.

    triggerChannel notNil ifTrue:[

	triggerChannel addDependent:self

    ]

!

setValue:anObject

    "set my value without notification."

    bufferedValue := anObject.

!

value

    "return my value"

    bufferedValue == NotYetAssigned ifTrue:[

	bufferedValue := subject value

    ].

    ^ bufferedValue

! !