I've been fighting this crazy problem for hours and have gotten nowhere. I have this problem in two completely different projects using a TCollection. When a new collection item is added, I need to initialize the values of that item. However, they're not defaulting at all. I'm even setting them in two completely different places, in the item's constructor, and in the collection's add function - neither of them are working. I can set the values once the items are there, but I need to set default values. I've done collections in the past and never had this problem, I must be missing something here...
unit JDGrids;
interface
uses
Classes, Windows, SysUtils, Grids, StrUtils;
type
TJDGridCol = class;
TJDGridCols = class;
TJDGridCols = class(TCollection)
private
fOnEvent: TNotifyEvent;
private
fOwner: TComponent;
procedure DoEvent;
property OnEvent: TNotifyEvent read fOnEvent write fOnEvent;
protected
function GetItem(Index: Integer): TJDGridCol;
procedure SetItem(Index: Integer; Value: TJDGridCol);
function GetOwner: TPersistent; override;
public
constructor Create(AOwner: TComponent);
destructor Destroy; override;
function Add: TJDGridCol;
procedure Assign(Source: TPersistent); override;
procedure Clear;
procedure Delete(Index: Integer);
property Items[Index: Integer]: TJDGridCol read GetItem write SetItem; default;
end;
TJDGridCol = class(TCollectionItem)
private
fOwner: TComponent;
fWidth: Integer;
fTitle: String;
fCols: TJDGridCols;
fOnEvent: TNotifyEvent;
fVisible: Bool;
procedure SetTitle(const Value: String);
procedure SetWidth(const Value: Integer);
procedure DoEvent;
property OnEvent: TNotifyEvent read fOnEvent write fOnEvent;
procedure SetVisible(const Value: Bool);
protected
function GetDisplayName: String; override;
public
constructor Create(AOwner: TJDGridCols);
destructor Destroy; override;
published
property Title: String read fTitle write SetTitle;
property Width: Integer read fWidth write SetWidth;
property Visible: Bool read fVisible write SetVisible;
end;
implementation
{ TJDGridCols }
constructor TJDGridCols.Create(AOwner: TComponent);
begin
inherited Create(TJDGridCol);
fOwner:= AOwner;
end;
destructor TJDGridCols.Destroy;
begin
inherited Destroy;
end;
function TJDGridCols.Add: TJDGridCol;
begin
Result:= TJDGridCol(inherited Add);
Result.fCols:= Self;
Result.fTitle:= 'Column '+IntToStr(Result.ID);
Result.fWidth:= 30;
Result.fVisible:= True;
DoEvent;
end;
procedure TJDGridCols.Assign(Source: TPersistent);
begin
inherited Assign(Source);
DoEvent;
end;
procedure TJDGridCols.Clear;
begin
inherited Clear;
DoEvent;
end;
procedure TJDGridCols.Delete(Index: Integer);
begin
inherited Delete(Index);
DoEvent;
end;
function TJDGridCols.GetItem(Index: Integer): TJDGridCol;
begin
Result:= TJDGridCol(inherited Items[Index]);
end;
function TJDGridCols.GetOwner: TPersistent;
begin
Result:= fOwner;
end;
procedure TJDGridCols.SetItem(Index: Integer; Value: TJDGridCol);
begin
inherited Items[Index]:= Value;
DoEvent;
end;
procedure TJDGridCols.DoEvent;
begin
if assigned(fOnEvent) then fOnEvent(Self);
end;
{ TJDGridCol }
constructor TJDGridCol.Create(AOwner: TJDGridCols);
begin
inherited Create(AOwner);
fOwner:= AOwner.fOwner;
fCols:= AOwner;
fTitle:= 'Column '+IntToStr(ID);
fWidth:= 30;
fVisible:= True;
end;
destructor TJDGridCol.Destroy;
begin
inherited Destroy;
end;
procedure TJDGridCol.DoEvent;
begin
if assigned(fOnEvent) then fOnEvent(Self);
end;
function TJDGridCol.GetDisplayName: String;
begin
Result:= fTitle;
end;
procedure TJDGridCol.SetTitle(const Value: String);
begin
fTitle:= Value;
DoEvent;
end;
procedure TJDGridCol.SetVisible(const Value: Bool);
begin
fVisible := Value;
DoEvent;
end;
procedure TJDGridCol.SetWidth(const Value: Integer);
begin
fWidth := Value;
DoEvent;
end;
end.
You are not overriding the constructor of TCollection, so TCollection.Add() cannot call your constructor. That is why you needed to have Add() set the default values.
Even then, you are setting default property values during construction, but you are not specifying those same default values in your property declarations. You need to do so for DFM streaming to work correctly.
You should also use TOwnedCollection instead of using TCollection directly. Let TOwnedCollection manage the Owner for you.
Try this:
unit JDGrids;
interface
uses
Classes, Windows, SysUtils, Grids, StrUtils;
type
TJDGridCol = class;
TJDGridCols = class(TOwnedCollection)
private
fOnEvent: TNotifyEvent;
private
procedure DoEvent;
property OnEvent: TNotifyEvent read fOnEvent write fOnEvent;
protected
function GetItem(Index: Integer): TJDGridCol;
procedure SetItem(Index: Integer; Value: TJDGridCol);
public
constructor Create(AOwner: TComponent); reintroduce;
destructor Destroy; override;
function Add: TJDGridCol; reintroduce;
procedure Assign(Source: TPersistent); override;
procedure Clear; reintroduce;
procedure Delete(Index: Integer); reintroduce;
property Items[Index: Integer]: TJDGridCol read GetItem write SetItem; default;
end;
TJDGridCol = class(TCollectionItem)
private
fWidth: Integer;
fTitle: String;
fOnEvent: TNotifyEvent;
fVisible: Bool;
procedure SetTitle(const Value: String);
procedure SetWidth(const Value: Integer);
procedure DoEvent;
procedure SetVisible(const Value: Bool);
property OnEvent: TNotifyEvent read fOnEvent write fOnEvent;
protected
function GetDisplayName: String; override;
function GetCols: TJDGridCols;
function GetOwner: TComponent;
public
constructor Create(AOwner: TCollection); override;
destructor Destroy; override;
published
property Title: String read fTitle write SetTitle;
property Width: Integer read fWidth write SetWidth default 30;
property Visible: Bool read fVisible write SetVisible default True;
end;
implementation
{ TJDGridCols }
constructor TJDGridCols.Create(AOwner: TComponent);
begin
inherited Create(AOwner, TJDGridCol);
end;
destructor TJDGridCols.Destroy;
begin
inherited Destroy;
end;
function TJDGridCols.Add: TJDGridCol;
begin
Result := TJDGridCol(inherited Add);
DoEvent;
end;
procedure TJDGridCols.Assign(Source: TPersistent);
begin
inherited Assign(Source);
DoEvent;
end;
procedure TJDGridCols.Clear;
begin
inherited Clear;
DoEvent;
end;
procedure TJDGridCols.Delete(Index: Integer);
begin
inherited Delete(Index);
DoEvent;
end;
function TJDGridCols.GetItem(Index: Integer): TJDGridCol;
begin
Result:= TJDGridCol(inherited Items[Index]);
end;
procedure TJDGridCols.SetItem(Index: Integer; Value: TJDGridCol);
begin
inherited SetItems(Index, Value);
DoEvent;
end;
procedure TJDGridCols.DoEvent;
begin
if Assigned(fOnEvent) then fOnEvent(Self);
end;
{ TJDGridCol }
constructor TJDGridCol.Create(AOwner: TCollection);
begin
inherited Create(AOwner);
fTitle := 'Column ' + IntToStr(ID);
fWidth := 30;
fVisible := True;
end;
destructor TJDGridCol.Destroy;
begin
inherited Destroy;
end;
procedure TJDGridCol.DoEvent;
begin
if Assigned(fOnEvent) then fOnEvent(Self);
end;
function TJDGridCol.GetDisplayName: String;
begin
Result := fTitle;
end;
function TJDGridCol.GetCols: TJDGridCols;
begin
Result := Collection as TJDGridCols;
end;
function TJDGridCol.GetOwner: TComponent;
begin
Result := GetCols.GetOwner as TComponent;
end;
procedure TJDGridCol.SetTitle(const Value: String);
begin
if fTitle <> Value then
begin
fTitle := Value;
DoEvent;
end;
end;
procedure TJDGridCol.SetVisible(const Value: Bool);
begin
if fVisible <> Value then
begin
fVisible := Value;
DoEvent;
end;
end;
procedure TJDGridCol.SetWidth(const Value: Integer);
begin
if fWidth <> Value then
begin
fWidth := Value;
DoEvent;
end;
end;
end.