Using object events as a means to synchronise data

[Rogier Knottenbelt]

Im trying to get userinterface objects to communicate with a datastore using event objects. The datastore is receiving new data and distributing it to anyone interested.

I can get all the inter object relations to work however, without any data transfer. I.e. I can create a notification that data is changed but I cant distribute the data with the notification. The code Im using is the following:

INTERFACE NewDataEv AS EVENT
  INHERIT IUNKNOWN
  METHOD NameChanged '(BYVAL Into$)
END INTERFACE

INTERFACE StoreData
  INHERIT IUNKNOWN
  METHOD DoReceiveANewName '(IN NewName$)
END INTERFACE

'--- Object defs
CLASS UserInterfaceClass1 AS EVENT

INSTANCE DataStoreObj AS StoreData

   INTERFACE NewDataEv AS EVENT
    INHERIT IUNKNOWN
    METHOD NameChanged '(BYVAL Into$)
      MSGBOX "1. Changed into " '+ Into$
    END METHOD

  END INTERFACE

  INTERFACE GetUserInput AS EVENT
    INHERIT IUNKNOWN

    METHOD SetDataStore (a AS StoreData)
      DataStoreObj = a
    END METHOD

    METHOD AskForAName
      MSGBOX "A new name created"
      DataStoreObj.DoReceiveANewName '("New Name")
    END METHOD
  END INTERFACE

END CLASS

'-------------
CLASS UserInterfaceClass2 AS EVENT

INSTANCE DataStoreObj AS StoreData

  INTERFACE GetUserInput AS EVENT
    INHERIT IUNKNOWN

    METHOD SetDataStore (a AS StoreData)
      DataStoreObj = a
    END METHOD

    METHOD AskForAName
      MSGBOX "A new name created"
      DataStoreObj.DoReceiveANewName '("New Name")
    END METHOD
  END INTERFACE

  INTERFACE NewDataEv AS EVENT
    INHERIT IUNKNOWN
    METHOD NameChanged '(BYVAL Into$)
      MSGBOX "2. Changed into " '+ Into$
    END METHOD
  END INTERFACE

END CLASS

'-------------
CLASS MyDataStore

  INTERFACE StoreData
    INHERIT IUNKNOWN
    METHOD DoReceiveANewName '(in NewName$)
      MSGBOX "A New Name..." + NewName$
      RAISEEVENT NewDataEv.NameChanged '("New name")
    END METHOD
  END INTERFACE

  EVENT SOURCE NewDataEv
END CLASS



FUNCTION PBMAIN()
  DIM oDataStore AS StoreData
  LET oDataStore = CLASS "MyDataStore"

' An UI object which reads input and displays it
  DIM oInputPart      AS GetUserInput : LET oInputPart      = CLASS "UserInterfaceClass1"  ' the input part of the UI object
  DIM oDisplayNameTxt AS NewDataEv    : LET oDisplayNameTxt = oInputPart                   ' the display part of the UI object
  oInputPart.SetDataStore (oDataStore)

' An UI object which displays changed data
  DIM oNameButton AS NewDataEv : LET oNameButton = CLASS "UserInterfaceClass2" ' Only display data

  EVENTS FROM oDataStore CALL oDisplayNameTxt
  EVENTS FROM oDataStore CALL oNameButton
  oInputPart.AskForAName
  EVENTS END oDisplayNameTxt
  EVENTS END oNameButton
END FUNCTION

I try to transfer data with the notifications (as indicated by the out commented method parameters). However, powerbasic gives a compile error when I remove the comment signs (Error 481 Mismatch with prior definition). What am I doing wrong?

If this data transfer is not possible can I determine where (i.e. which object instance) the notification came from so I can get the data from the notifier?


Thanks in advance
Rogier

[Michael Mattias]

I have no idea if this "works" but using PB/Win, 9.0.1 ...
1. I changed all the 'typed' string variables from "$" suffix to AS STRING, as the doc says that's what METHOD wants
2. I dropped all the "IN" in the parameter definitions as the doc does not allow for the inclusion of the word "IN" in those parameter descriptions.
3. I dropped the BYVALs in the params (because I felt like it. I had no good reason).

....and the program compiles and executes.

' test_method.bas


INTERFACE NewDataEv AS EVENT
  INHERIT IUNKNOWN
  METHOD NameChanged (Into AS STRING)
 '  METHOD NameChanged (BYVAL Into AS STRING$)
END INTERFACE

INTERFACE StoreData
  INHERIT IUNKNOWN
  METHOD DoReceiveANewName (NewName AS STRING)
END INTERFACE

'--- Object defs
CLASS UserInterfaceClass1 AS EVENT

INSTANCE DataStoreObj AS StoreData

   INTERFACE NewDataEv AS EVENT
    INHERIT IUNKNOWN
    METHOD NameChanged (Into AS STRING)
      MSGBOX "1. Changed into " '+ Into$
    END METHOD

  END INTERFACE

  INTERFACE GetUserInput AS EVENT
    INHERIT IUNKNOWN

    METHOD SetDataStore (a AS StoreData)
      DataStoreObj = a
    END METHOD

    METHOD AskForAName
      MSGBOX "A new name created"
      DataStoreObj.DoReceiveANewName ("New Name")
    END METHOD
  END INTERFACE

END CLASS

'-------------
CLASS UserInterfaceClass2 AS EVENT

INSTANCE DataStoreObj AS StoreData

  INTERFACE GetUserInput AS EVENT
    INHERIT IUNKNOWN

    METHOD SetDataStore (a AS StoreData)
      DataStoreObj = a
    END METHOD

    METHOD AskForAName
      MSGBOX "A new name created"
      DataStoreObj.DoReceiveANewName ("New Name")
    END METHOD
  END INTERFACE

  INTERFACE NewDataEv AS EVENT
    INHERIT IUNKNOWN
    METHOD NameChanged (INTO AS STRING)
      MSGBOX "2. Changed into " '+ Into$
    END METHOD
  END INTERFACE

END CLASS

'-------------
CLASS MyDataStore

  INTERFACE StoreData
    INHERIT IUNKNOWN
    METHOD DoReceiveANewName (NewName AS STRING)
      MSGBOX "A New Name..." + NewName$
      RAISEEVENT NewDataEv.NameChanged ("New name")
    END METHOD
  END INTERFACE

  EVENT SOURCE NewDataEv
END CLASS



FUNCTION PBMAIN()
  DIM oDataStore AS StoreData
  LET oDataStore = CLASS "MyDataStore"

' An UI object which reads input and displays it
  DIM oInputPart      AS GetUserInput : LET oInputPart      = CLASS "UserInterfaceClass1"  ' the input part of the UI object
  DIM oDisplayNameTxt AS NewDataEv    : LET oDisplayNameTxt = oInputPart                   ' the display part of the UI object
  oInputPart.SetDataStore (oDataStore)

' An UI object which displays changed data
  DIM oNameButton AS NewDataEv : LET oNameButton = CLASS "UserInterfaceClass2" ' Only display data

  EVENTS FROM oDataStore CALL oDisplayNameTxt
  EVENTS FROM oDataStore CALL oNameButton
  oInputPart.AskForAName
  EVENTS END oDisplayNameTxt
  EVENTS END oNameButton
END FUNCTION

[Rogier Knottenbelt]

Thanks Michael

The docs rule! I'll play around with the ins&outs of the byrefs, byvals, etc, just to make sure I get it all and will post the result (prob also in the source code forum)

[Michael Mattias]

>I'll play around with the ins&outs of the byrefs, byvals, etc

Point of call overrides?

Point-of-call overrides (BYVAL, BYRE, BYCOPY ) are not something one "plays around with." And in procedure/method/property definitions, they are what they are, as documented.

Just use the generated *.INC file or your own procedure/method/property header parameter definitions, eschewing point-of-call overrides and letting the compiler handle it until you fully understand the ramifications of doing so.

As far as how you DEFINE your procedure/method/property parameters (BYVAL or BYREF), well, that's a function of your application.

MCM

[Rogier Knottenbelt]

Play time stopped ..... for a while ...

Hi Michael,

At long last some more time on my sleeve. I posted an example in the Source Code forum (http://www.powerbasic.com/support/pb...ad.php?t=42079)

One note on the absence of any IN&OUTs:

My programming background goes back to embedded programming. One of the 'tricks' used to speed up processing is to pass big chunks of data as a BYREF to a procedure, even if the data is not to be changed. This saves making a copy of the data every time the sub is called.
In the docs I read that putting an IN statement before a BYREF does protect the original data from being changed. I.e. in the Method/End Method help section it reads:

you may freely assign new values to BYVAL/IN parameters. They will simply be discarded when the METHOD exits

I like the idea of indicating a BYREF parameter, which is meant to be a BYVAL, by putting an IN before it. I don't like it that I can then easily change it anyway and the changes will be discarded although its a BYREF...

Too confusing for me so I choose not to use the IN&OUT syntax at this time