redt1里面有一些文本.
通过代码实现将redt1的内容原封不动的复制到redt2中.
用CopyToClipboard和PasteFromClipboard只能粘贴一次.
比如:
for i:=0 to 10 do
begin
redt1.selectAll;
redt1.CopyToClipboard;
redt2.PasteFromClipBoard;
end;
实际只粘贴了一次.

从网上找到一个方法:

function EditStreamInCallback(dwCookie: Longint; pbBuff: PByte;
cb: Longint; var pcb: Longint): Longint; Stdcall;
var
  theStream: TStream;
  dataAvail: LongInt;
begin
  theStream := TStream(dwCookie);
  with theStream do begin
    dataAvail := Size - Position;
    Result := 0; {assume everything is ok}
    if dataAvail <= cb then begin
      pcb := Read(pbBuff^, dataAvail);
      if pcb <> dataAvail then {couldn't read req. amount of bytes}
        result := E_FAIL;
    end
    else begin
      pcb := Read(pbBuff^, cb);
      if pcb <> cb then
        result := E_FAIL;
    end;
  end;
end;

Function EditStreamOutCallback(dwCookie: Longint; pbBuff: PByte;
    cb: Longint; var pcb: Longint): Longint; stdcall;
var
   theStream: TStream;
begin
   theStream := TStream(dwCookie);

   with theStream do begin
     If cb > 0 Then
       pcb := Write(pbBuff^, cb);
     Result := 0;
   end;
end;

Procedure GetRTFSelection (aRichEdit: TRichEdit; intoStream: TStream);
Var
  editstream: TEditStream;
Begin
  With editstream Do Begin
    dwCookie:= Longint(intoStream);
    dwError:= 0;
    pfnCallback:= EditStreamOutCallBack;
  end;
  aRichedit.Perform( EM_STREAMOUT, SF_RTF or SFF_SELECTION,longint(@editstream));
End;

Procedure PutRTFSelection (aRichEdit: TRichEdit; sourceStream: TStream);
Var
  editstream: TEditStream;
Begin
  sourceStream.Position := 0;
  With editstream Do Begin
    dwCookie:= Longint(sourceStream);
    dwError:= 0;
    pfnCallback:= EditStreamInCallBack;
  end;
  aRichedit.Perform( EM_STREAMIN, SF_RTF or SFF_SELECTION,  longint(@editstream));
End;

调用:
var
  aMemStream:TMemoryStream;
  I:Integer;
begin
  redt1.SelectAll;
  aMemStream := TMemoryStream.Create;
  try
    getRTFSelection (redt1, aMemStream);
    for  I:=0 to 10 do
      putRTFSelection (redt2, aMemStream);
  finally
    aMemStream.Free;
  end;
end;
 

本文来源：http://blog.csdn.net/mastersky/archive/2007/07/04/1678816.aspx