Delphi从接口通知事件

Question

I'm here again for a question about notification. I've the followinf interface:

unit TblInterface;

interface

uses
  System.TypInfo, Vcl.Forms, RzPanel, Winapi.Windows, Winapi.Messages,
  UserMessages, Vcl.Dialogs, Vcl.Controls;

type

  TFrameType = (ftList, ftDetail);

  TFrameInfo = record
    Frame: TFrame;
    FrameType: TFrameType;
  end;

  TFrameClass = class of TFrame;

  ITabella = interface
  ['{D21924F9-BB41-493B-B06D-0908C0CA73D8}']
    function GetCurrentActiveFrameType: TFrameInfo;
    procedure CreateLstFrame(ParentForm: TForm; Frame: TFrameClass);
    procedure CreateDtlFrame(ParentForm: TForm; Frame: TFrameClass);
    procedure DestroyLstFrame;
    procedure DestroyDtlFrame;
    procedure BringFrameToFront(FrameType: TFrameType);
    procedure OnDoubleClick;
  end;

  TTabella = class(TInterfacedObject, ITabella)
  private
    FLst: TFrame;
    FDtl: TFrame;
    ActFrame: TFrameInfo;
    function GetCurrentActiveFrameType: TFrameInfo;
    procedure CreateLstFrame(ParentForm: TForm; Frame: TFrameClass);
    procedure CreateDtlFrame(ParentForm: TForm; Frame: TFrameClass);
    procedure DestroyLstFrame;
    procedure DestroyDtlFrame;
    procedure BringFrameToFront(FrameType: TFrameType);
    procedure OnDoubleClick;
  end;

implementation

{ TTabella }

{ Creazione frame lista }
procedure TTabella.CreateLstFrame(ParentForm: TForm; Frame: TFrameClass);
begin
  FLst := Frame.Create(ParentForm);
  FLst.Parent := ParentForm;
  FLst.Align := alClient;
end;

{ Creazione frame dettaglio }
procedure TTabella.CreateDtlFrame(ParentForm: TForm; Frame: TFrameClass);
begin
  FDtl := Frame.Create(ParentForm);
  FDtl.Parent := ParentForm;
  FDtl.Align := alClient;
end;

{ Distruzione frame lista }
procedure TTabella.DestroyLstFrame;
begin
  FLst.Free;
end;

{ Distruzione frame dettaglio }
procedure TTabella.DestroyDtlFrame;
begin
  FDtl.Free;
end;

{ Porta in primo piano il frame richiesto }
procedure TTabella.BringFrameToFront(FrameType: TFrameType);
begin
  case FrameType of
    ftList: begin
      FLst.BringToFront;
      ActFrame.Frame := FLst;
    end;
    ftDetail: begin
      FDtl.BringToFront;
      ActFrame.Frame := FDtl;
    end;
  end;
  ActFrame.FrameType := FrameType;
end;

{ Restiruisce il frame attivo }
function TTabella.GetCurrentActiveFrameType: TFrameInfo;
begin
  Result := ActFrame;
end;

procedure TTabella.OnDoubleClick;
begin
  BringFrameToFront(ftList);
end;

end.

In the interface I create two frames that are used to display list and detail of some database tables. Form interface I create, brig to front the correct frame and destroy it. At this point I need to notify events to the frames created, but I don't know how to do this king of job. For example I need to notify to the detail frame that a button was pressed in the list frame.

How can I achieve this task?

Answer 1

There are at least 2 ways to do that. First, which i will recommend, is using another Interface; Second way is using procedure of object, which we handle event. Let's put the hands in the batter!

1. Declare a new Interface before ITabella with the methods will want to notify

    IProcessor=Interface {Shift+Ctrl+G} procedure Select; procedure Search(); 

A very basic example to handle Click event and same Search event, to call the frame ftList Then we implement the methods in descendant classes

TProcessTabellaPeople=class(TnterfacedObject,IProcessor)
procedure Select; virtual; abstract;
procedure Search; virtual; abstract;
..
end;
TProcessTabellaCustomer=class(TProcessTabellaPeople)
procedure Select; virtual; abstract;
procedure Search; virtual; abstract;
..
end;
{remove abstract clause to implement the methods using Shift+Ctrl+C,
or keep them to late binding in descendant Classes}

Add a reference to IProcessor in ITabella

ITabella = interface
  ['{D21924F9-BB41-493B-B06D-0908C0CA73D8}']
    fProc:IProcessor ;
    function GetCurrentActiveFrameType: TFrameInfo;
    procedure CreateLstFrame(ParentForm: TForm; Frame: TFrameClass);
    procedure CreateDtlFrame(ParentForm: TForm; Frame: TFrameClass);
    procedure DestroyLstFrame;
    procedure DestroyDtlFrame;
    procedure BringFrameToFront(FrameType: TFrameType);
    procedure OnDoubleClick;
    **procedure clickSelect;**
    **property Proc:IProcessor read fProc write fProc;**
  end;

Propagates TTabela.OnDoubleClick for corresponding IProcessor method

procedure TTabella.OnDoubleClick;
begin
  BringFrameToFront(ftList);
  If Assigned(fProc) then Proc.Search(); {Call IProcessorMethod}
end;
procedure TTabella.ClickSelect;
begin
If Assigned(fProc) then Proc.Select(); {Call IProcessorMethod}
end;

using the interface properly On Create of TTabela pass the Processor, for example

Var Tabella1: ITabella;
Begin
Tabela1:=TTabela.create();
Tabela1.proc:=TProcessor
end;

At this point I will recommend to you implement the constructor create passing the IProcessTabellaCustomer.create; {don't need to free using Interface vartype}

For onClick of TButton do like that:

Tabela1.ClickSelect;

2. Use procedure of object contents or TNotify class methods You can declare ClassMethods like this

    TSelectMethod = procedure(name:String; Sender:TObject) of object; ITabella = interface ['{D21924F9-BB41-493B-B06D-0908C0CA73D8}'] property Select:TSelectMethod read fSelect write fSelect; property Search:TNotifyEvent; end; 

Note that TNotifyEvent signs

TNotifyEvent= procedure (Sender:TObject)of Object;

While in the form you create some methods with the same signs of Events Handler,

procedure TForm1.btnSearchClick(Sender:TObject)of Object; //*the same sign of TButtonClick, for example*
begin
end;
procedure TForm1.ShowSelected(name:String; Sender:TObject) of object;//*customized sign with new parameters
begin
showmessage(Format('Selected name%s',[name]));
end;

You can attribute the procedures for fields in run time

Tabella1:=TTabela.create();
Tabella1.Select:=Form1.btnSelectClick;
Tabella1.Search:=Form1.btnSearchClick;