Using TOwnedCollection descendant in Delphi - delphi

Question

I'm trying to create a custom component with a collection property. However if I try to open the collection editor during design time by clicking "..." button in object inspector, nothing happens. What I am missing?
Here's my TCollection descendant:
TMyCollection = class(TOwnedCollection)
private
function GetItem(Index: Integer): TMyCollectionItem;
procedure SetItem(Index: Integer; const Value: TMyCollectionItem);
public
function Add : TMyCollectionItem;
property Items[Index: Integer]: TMyCollectionItem read GetItem write SetItem;
end;
And the item:
TMyCollectionItem = class(TCollectionItem)
private
FValue: integer;
protected
function GetDisplayName: string; override;
public
procedure Assign(Source: TPersistent); override;
constructor Create(Collection: TCollection); override;
destructor Destroy; override;
published
property Value : integer read FValue write FValue;
end;

Answer 1

Your class definitions look correct so with out seeing the entire implementation I don't know what the problem is.
Here is a simple unit I've written that uses TOwnedCollection, TCollectionItem and TComponent.
I know this unit works. Use it as a basis for checking your code.
unit rmMultiStrings;
interface
uses classes, sysutils;
type
ErmMultiStringNameException = Exception;
TrmMultiStringsCollection = class;
TrmMultiStringCollectionItem = class(TCollectionItem)
private
fItemDesc: string;
fItemName: string;
fData : TStringList;
fMultiStrings : TrmMultiStringsCollection;
function GetStrings: TStringList;
function GetStringText: String;
procedure SetItemName(const Value: string);
procedure SetStrings(const Value: TStringList);
procedure SetStringText(const Value: String);
public
constructor Create(Collection: TCollection); override;
destructor Destroy; override;
procedure Assign(Source: TPersistent); override;
published
property ItemName : string read fItemName write SetItemName;
property Description : string read fItemDesc write fItemDesc;
property Strings : TStringList read GetStrings write SetStrings stored false;
property Text : String read GetStringText write SetStringText;
end;
TrmMultiStringsCollection = class(TOwnedCollection)
private
function GetItem(AIndex: integer): TrmMultiStringCollectionItem;
procedure SetItem(AIndex: integer; const Value: TrmMultiStringCollectionItem);
public
function Add: TrmMultiStringCollectionItem;
function IndexOf(ItemName:string):integer;
function ValueOf(ItemName:string):String;
function ValueOfIndex(aIndex:integer):string;
procedure Assign(Source: TPersistent); override;
property Items[AIndex: integer] : TrmMultiStringCollectionItem read GetItem write SetItem;
end;
TrmMultiStrings = class(TComponent)
private
fData : TrmMultiStringsCollection;
procedure SetData(const Value: TrmMultiStringsCollection);
public
constructor Create(AOwner: TComponent); override;
destructor Destroy; override;
function IndexOf(ItemName:string):integer;
function ValueOf(ItemName:string):String;
function ValueOfIndex(aIndex:integer):string;
published
property Data : TrmMultiStringsCollection read fData write SetData;
end;
procedure Register;
implementation
procedure Register;
begin
RegisterClass(TrmMultiStringsCollection);
RegisterClass(TrmMultiStringCollectionItem);
RegisterComponents('rmConcordia', [TrmMultiStrings]);
end;
{ TrmMultiStringCollectionItem }
procedure TrmMultiStringCollectionItem.Assign(Source: TPersistent);
var
wSrc : TrmMultiStringCollectionItem;
begin
if Source is TrmMultiStringCollectionItem then
begin
wSrc := TrmMultiStringCollectionItem(Source);
ItemName := wSrc.ItemName;
Description := wSrc.Description;
Text := wSrc.Text;
end
else
inherited;
end;
constructor TrmMultiStringCollectionItem.Create(Collection: TCollection);
begin
inherited;
fMultiStrings := TrmMultiStringsCollection(Collection);
fData := TStringList.create;
end;
destructor TrmMultiStringCollectionItem.Destroy;
begin
fData.free;
inherited;
end;
function TrmMultiStringCollectionItem.GetStrings: TStringList;
begin
result := fData;
end;
function TrmMultiStringCollectionItem.GetStringText: String;
begin
result := fData.Text;
end;
procedure TrmMultiStringCollectionItem.SetItemName(const Value: string);
begin
if (fItemName <> Value) then
begin
if fMultiStrings.IndexOf(Value) = -1 then
fItemName := Value
else
raise ErmMultiStringNameException.Create('Item name already exists');
end;
end;
procedure TrmMultiStringCollectionItem.SetStrings(
const Value: TStringList);
begin
fData.Assign(Value);
end;
procedure TrmMultiStringCollectionItem.SetStringText(const Value: String);
begin
fData.Text := Value;
end;
{ TrmMultiStringsCollection }
function TrmMultiStringsCollection.Add: TrmMultiStringCollectionItem;
begin
result := TrmMultiStringCollectionItem(inherited Add);
result.ItemName := 'Item_'+inttostr(NextID);
end;
procedure TrmMultiStringsCollection.Assign(Source: TPersistent);
var
wSrc : TrmMultiStringsCollection;
loop : integer;
begin
if (source is TrmMultiStringsCollection) then
begin
wSrc := TrmMultiStringsCollection(Source);
Clear;
for loop := 0 to wSrc.Count - 1 do
Add.Assign(wSrc.Items[loop]);
end
else
inherited;
end;
function TrmMultiStringsCollection.GetItem(
AIndex: integer): TrmMultiStringCollectionItem;
begin
result := TrmMultiStringCollectionItem(inherited Items[AIndex]);
end;
function TrmMultiStringsCollection.IndexOf(ItemName: string): integer;
var
loop : integer;
begin
result := -1;
loop := 0;
while (result = -1) and (loop < Count) do
begin
if (CompareText(Items[loop].ItemName, ItemName) = 0) then
result := loop
else
inc(loop);
end;
end;
procedure TrmMultiStringsCollection.SetItem(AIndex: integer; const Value: TrmMultiStringCollectionItem);
begin
inherited SetItem(AIndex, Value)
end;
function TrmMultiStringsCollection.ValueOf(ItemName: string): String;
begin
result := ValueOfIndex(IndexOf(ItemName));
end;
function TrmMultiStringsCollection.ValueOfIndex(aIndex: integer): string;
begin
if (aIndex >= 0) and (aIndex < Count) then
result := Items[aIndex].Text
else
result := '';
end;
{ TrmMultiStrings }
constructor TrmMultiStrings.Create(AOwner: TComponent);
begin
inherited;
fData := TrmMultiStringsCollection.Create(self, TrmMultiStringCollectionItem);
end;
destructor TrmMultiStrings.Destroy;
begin
fData.Free;
inherited;
end;
function TrmMultiStrings.IndexOf(ItemName: string): integer;
begin
result := Data.IndexOf(ItemName);
end;
procedure TrmMultiStrings.SetData(const Value: TrmMultiStringsCollection);
begin
fData.Assign(Value);
end;
function TrmMultiStrings.ValueOf(ItemName: string): String;
begin
result := Data.ValueOf(ItemName);
end;
function TrmMultiStrings.ValueOfIndex(aIndex: integer): string;
begin
result := Data.ValueOfIndex(aIndex);
end;
end.