type
TMyMemo = class(TMemo)
private
FLastSelStart : Integer;
FLastSelLength : Integer;
procedure WMLButtonDown(var Message: TWMLButtonDown);
message WM_LBUTTONDOWN;
published
property LastSelStart : Integer read FLastSelStart
write FLastSelStart;
property LastSelLength : Integer read FLastSelLength
write FLastSelLength;
end;

如下实现 WMLButtonDown:

procedure TMyMemo.WMLButtonDown(var Message: TWMLButtonDown);
var
Ch : Integer;
begin
if SelLength > 0 then begin
Ch := LoWord(Perform(EM_CHARFROMPOS,0,
MakeLParam(Message.XPos,Message.YPos)));
LastSelStart := SelStart;
LastSelLength := SelLength;
if (Ch >= SelStart) and (Ch <= SelStart+SelLength-1) then
BeginDrag(True)
else
inherited;
end
else
inherited;
end;

现在，将组件打包， 在Delphi中开始一个新的工程并下移TMyMemos
在他们中都作个OnDragOver 事件处理句柄，如下:

procedure TForm1.MyMemo1DragOver(Sender, Source: TObject; X, Y: Integer;
State: TDragState; var Accept: Boolean);
begin
Accept := Source is TMyMemo;
end;

在他们中都作个OnDragDrop事件处理句柄，如下:

procedure TForm1.MyMemo1DragDrop(Sender, Source: TObject;
X, Y: Integer);
var
Dst, Src : TMyMemo;
Ch : Integer;
Temp : String;
begin
Dst := Sender as TMyMemo;
Src := Source as TMyMemo;
Ch := LoWord(Dst.Perform(EM_CHARFROMPOS,0,MakeLParam(X,Y)));
if (Src = Dst) and (Ch >= Src.LastSelStart) and
(Ch <= Src.LastSelStart+Src.LastSelLength-1) then
Exit;
Dst.Text := Copy(Dst.Text,1,Ch)+Src.SelText+
Copy(Dst.Text,Ch+1,Length(Dst.Text)-Ch);
Temp := Src.Text;
Delete(Temp,Src.LastSelStart+1,Src.LastSelLength);
Src.Text := Temp;
end;

运行程序并加些文本到Memo中，观察当你在两个Memo间拖放文本时发生了什么，甚或是在同一Memo组件的不同位置拖放文本。