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Why when I assign SelText with Memo1.Seltext:=FormatDateTime('hh/nn/ss', Now) CanUndo=False? I've tried to add Memo1.Modified:=True; but CanUndo is still false. So i red SetSelText procedure from StdCtrls and lparam=0, but in hel borlan says thal ord(False{BOOL False, not Boolean False})=0 so I wrote custom component that sends message wit lparam=10 and still canundo is false. What i do wrong or what I should do to make undo possible (maybe make list of undo operations, but that will be too much for my little program)?

The following code works.

Code: Select all

S := FormatDateTime('hh/nn/ss', Now);
SendMessage(Memo1.Handle, EM_REPLACESEL, 1, LPARAM(PChar(S)));


Cheers,
Kambiz

This is very good, but this isn't good in my program (it happends) so i will contretize it a bit:

How to make custom component based on TMemo that seltext property will work properly (canundo)?

One more thing: can you test it:

Code: Select all

unit HMemo;

interface

uses
  Windows, Messages, SysUtils, Classes, Controls, StdCtrls;

type
  THMemo = class(TMemo)
  private
    procedure SetSelText(const Value: string); reintroduce;
  protected
    { Protected declarations }
  public
    procedure SetSelTextBuf(Buffer: PChar);
  published
    constructor Create(AOwner: TComponent); reintroduce;
    property SelText read GetSelText write SetSelText;
  end;

procedure Register;

implementation

procedure Register;
begin
  RegisterComponents('HAKGERSoft Components', [THMemo]);
end;

{ THMemo }

constructor THMemo.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
end;

procedure THMemo.SetSelText(const Value: string);
begin
  SendMessage(Handle, EM_REPLACESEL, 1, Longint(PChar(Value)));
end;

procedure THMemo.SetSelTextBuf(Buffer: PChar);
begin
  SendMessage(Handle, EM_REPLACESEL, 1, LongInt(Buffer));
end;

end.


And one more thing: Does typecasting will THMemo to TCustomMemo will change THMemo's SetSelText to TCustomEdit's SetSelText?

The THMemo will work properly, however the SelText property will work like the base class. Because the SetSelText method of the ancestor is a private and static method.

If you typecast a class to its base or child class and then call a virtual method, the typecast has no effect (because of polymorphism). However, for the static methods, method of typecast will be called.

Kambiz

OK, then what I Should do to make THMemo to using my SetSelTtext? reintroduce doesn't isn't enought?

Tehe reintreduce directive will not work because the base method is private.

Why you don't use a procedure like the following one?

Code: Select all

procedure SetSelText(Edit: TCustomEdit; const S: String);
begin
   SendMessage(Edit.Handle, EM_REPLACESEL, 1, LPARAM(PChar(S)));
end;

Kambiz

These seems like a good way, but i'm thinking about this:

Code: Select all

unit HMemo;

interface

uses
  Windows, Messages, SysUtils, Classes, Controls, StdCtrls;

type
  THMemo = class(TMemo)
  private
    procedure SetSelTextMy(const Value: string);
  protected
    { Protected declarations }
  public
    procedure SetSelTextBuf(Buffer: PChar);
  published
    constructor Create(AOwner: TComponent); reintroduce;
    property SelText read GetSelText write SetSelTextMy;
  end;

procedure Register;

implementation

procedure Register;
begin
  RegisterComponents('HAKGERSoft Components', [THMemo]);
end;

{ THMemo }

constructor THMemo.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
end;

procedure THMemo.SetSelTextMy(const Value: string);
begin
  SendMessage(Handle, EM_REPLACESEL, 1, Longint(PChar(Value)));
end;

procedure THMemo.SetSelTextBuf(Buffer: PChar);
begin
  SendMessage(Handle, EM_REPLACESEL, 1, LongInt(Buffer));
end;

end.

will it work as i want?

You should impelement the GetSelText method also, because in base class it is private.

Kambiz

It doesn't matters, it works! Now I know how make what I want.