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Reference parent property of custom type

Posted on 2006-10-26
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Last Modified: 2013-11-23
This is a cut down version of the sort of thing I have

MyType = ( item1, item2, item3);

TMyObject = class( TObject)
  private
    MyType: TMyType;  // I want to remove this property

    function GetMyType: TMyType;
  public
    property MyType: TMyType read GetMyType;
  end;

TMyObjectList = class( TObjectList)
  private
    MyType: TMyType;  // i want to be able to reference this parent property from the objects in the objectlist
  end;


What I don't like is the fact that I have the property MyType in both the parent and child.
I would rather just keep it in the parent (objectlist), anmd be able to reference it from the child

Obviously I know this code below will not compile, but hopefully someone gets the idea of what I want to do.
I would assume that this might normally be done using a "class property", but they don't exist in delphi.

function TMyObject.GetMyType: TMyType;
begin
  Result := Parent.MyType
end;
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Question by:mikelittlewood
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7 Comments
 
LVL 27

Expert Comment

by:kretzschmar
ID: 17810258
?? what is the parent???
0
 
LVL 15

Author Comment

by:mikelittlewood
ID: 17810285
The TMyObjectList is the parent holding n number of TMyObject's
0
 
LVL 15

Author Comment

by:mikelittlewood
ID: 17810291
Currently both the TMyObjectList AND each TMyObject have a property MyType, but I want to remove the property from the child TMyObject and reference the property MyType in the parent TMyObjectList from within the child.
0
 
LVL 27

Expert Comment

by:kretzschmar
ID: 17810320
maybe this way??

TMyObjectList = class( TObjectList)
  published
    property MyType: TMyType[Index] read GetMyType;  //not sure about the syntax here (just from head)
  end;


function TMyObjectList.GetMyType(index : integer) : TMyType
begin
  //check bounds
  if (index < 0) or (index > count) then
   raise exception.create('Index out of bounds');
  result := TMyObject(items[index]).MyType;
end;

just from head

meikl ;-)
0
 
LVL 27

Accepted Solution

by:
kretzschmar earned 250 total points
ID: 17810333
>TMyObject and reference the property MyType in the parent TMyObjectList from within the child
oops the other direction, thinking . . .

you need an attribute in your TMyObject, which references the objectlist where it is added into.
you may keep in mind that it could be added into multiple lists
-> so the TMyObject should add/remove itself

meikl ;-)
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