How to instantiate different frame types? - delphi

Question

I'm here again with frames.
I've this main form:
It's only a simple form created in order to understand the use of frames.
With the two buttons on the top of the form I would like to open this two frames:
Frame1
and Frame2
here is the code the simple code of the first frame:
unit AppFrame1;
interface
uses
Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants,
System.Classes, Vcl.Graphics, Vcl.Controls, Vcl.Forms, Vcl.Dialogs,
Vcl.StdCtrls;
type
TFrame1 = class(TFrame)
lblFrame1: TLabel;
private
{ Private declarations }
public
{ Public declarations }
end;
implementation
{$R *.dfm}
end.
and here is the code of the second frame:
unit AppFrame2;
interface
uses
Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants,
System.Classes, Vcl.Graphics, Vcl.Controls, Vcl.Forms, Vcl.Dialogs,
Vcl.StdCtrls;
type
TFrame2 = class(TFrame)
lblFrame2: TLabel;
private
{ Private declarations }
public
{ Public declarations }
end;
implementation
{$R *.dfm}
end.
So nothing special in the two frames.
in order to open the frames from the main form I've created an interface like this:
unit FramesManager;
interface
uses
Vcl.Forms, Vcl.StdCtrls, Vcl.ExtCtrls, Vcl.Controls;
type
TFrameClass = class(TFrame)
end;
IFrameManager = interface
['{A00E0D1B-3438-4DC4-9794-702E8302B567}']
procedure CreateGenericFrame(AParentPanel: TPanel; AFrameClass: TFrameClass);
procedure DestroyGenericFrame();
end;
TFrameManager = class(TInterfacedObject, IFrameManager)
private
FGenericFrame: TFrameClass;
procedure CreateGenericFrame(AParentPanel: TPanel; AFrameClass: TFrameClass);
procedure DestroyGenericFrame();
public
property Frame: TFrameClass read FGenericFrame write FGenericFrame;
end;
implementation
{ TFrameManagement }
procedure TFrameManager.CreateGenericFrame(AParentPanel: TPanel;
AFrameClass: TFrameClass);
begin
FGenericFrame := AFrameClass.Create(AParentPanel);
FGenericFrame.Parent := AParentPanel;
FGenericFrame.Align := alClient;
end;
procedure TFrameManager.DestroyGenericFrame;
begin
FGenericFrame.Free;
end;
end.
At this point my intension is to use the interface for create the two frames but I can't realize how to reach this task.
My main form code is this:
unit Main;
interface
uses
Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants,
System.Classes, Vcl.Graphics, Vcl.Controls, Vcl.Forms, Vcl.Dialogs,
Vcl.ExtCtrls, FramesManager, Vcl.StdCtrls, AppFrame1, AppFrame2;
type
TfrmMain = class(TForm)
pnlCommands: TPanel;
pnlFrames: TPanel;
btnCrtFrame1: TButton;
btnCrtFrame2: TButton;
procedure FormCreate(Sender: TObject);
procedure btnCrtFrame1Click(Sender: TObject);
procedure btnCrtFrame2Click(Sender: TObject);
private
FFrame: IFrameManager;
public
{ Public declarations }
end;
var
frmMain: TfrmMain;
implementation
{$R *.dfm}
procedure TfrmMain.FormCreate(Sender: TObject);
begin
FFrame := TFrameManager.Create;
end;
procedure TfrmMain.btnCrtFrame1Click(Sender: TObject);
begin
FFrame.CreateGenericFrame(pnlFrames, TFrame1);
end;
procedure TfrmMain.btnCrtFrame2Click(Sender: TObject);
begin
FFrame.CreateGenericFrame(pnlFrames, TFrame2);
end;
end.
When I try co compile the project I receive this errors:
[dcc32 Error] Main.pas(41): E2010 Incompatible types: 'TFrameClass' and 'class of TFrame1'
[dcc32 Error] Main.pas(46): E2010 Incompatible types: 'TFrameClass' and 'class of TFrame2'
So I would like to understand how to create the two frames from the main.
How can I assign the right object type to the TFrameClass?
I've tought about generics, but I have not idea on how to implement this kind of interface in order to open a "generic" frame that can be created form the main when the use choose to open it.
I hope I have explained clearly my problem, but I know that it may seem complicate to understand.

Answer 1

type
TFrameClass = class(TFrame)
end;
Your TFrameClass declaration is wrong. Right now it is declared as a descendant of TFrame which is just another class.
What you need is a class reference:
type
TFrameClass = class of TFrame;
Because both TFrame1 and TFrame2 descend from TFrame, both can be put into a TFrameClass variable.
But I am pretty sure this TFrameClass already exists somewhere in the VCL in which case you do not have to redeclare this type.
Subsequently, the type of FGenericFrame private field needs to become TFrame instead of TFrameClass.
(Also, this has nothing to do with Generics.)