在Memo里实现文本的拖放

在Memo里实现文本的拖放
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;
Make the implementation of WMLButtonDown look like this:
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;
Now, install this component into a package, start a brand new project
in Delphi 3 and drop two TMyMemos down.
Make them both have an OnDragOver event handler looking like this:
procedure TForm1.MyMemo1DragOver(Sender,Source:TObject;X,Y:Integer;State:TDragState;var Accept:Boolean);
begin
Accept:=Source is TMyMemo;
end;
Make them both have an OnDragDrop event handler looking like this:
procedure TForm1.MyMemo1DragDrop(Sender, Source: TObject;X,Y:Integer);
var
Dst,Src:TMyMemo;
Ch :Integer;
Temp :String;
begin
Dst:=SenderasTMyMemo;
Src:=SourceasTMyMemo;
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;