Mega Code Archive
Drag - drop example
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Have you ever been using WinAmp? If you haven't, I could tell you that it's a widely spread freeware
music-mediaplayer, where you can have a tracklist with your favourite songs. The songs in this list could very
easy be moved to any position with the use of drag & drop functionality.
This example shows how to implement it with Delphi.
{-----------------------------------------------------------------------------
Unit Name: Unit1
Author: Mats Asplund
Description: Drag & drop example with a Listbox as source and destination.
-----------------------------------------------------------------------------}
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
StdCtrls;
type
TForm1 = class(TForm)
ListBox1: TListBox;
procedure ListBox1DragOver(Sender, Source: TObject; X, y: Integer;
State: TDragState; var Accept: Boolean);
procedure ListBox1DragDrop(Sender, Source: TObject; X, y: Integer);
procedure ListBox1MouseDown(Sender: TObject; Button: TMouseButton;
Shift: TShiftState; X, y: Integer);
procedure FormCreate(Sender: TObject);
private
FromPos, ToPos: TPoint;
procedure MoveItem(FromPos, ToPos: Integer);
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.DFM}
procedure TForm1.FormCreate(Sender: TObject);
begin
ListBox1.DragMode:= dmAutomatic;
// Fill the listbox with some items
ListBox1.Items.Add('Item 1');
ListBox1.Items.Add('Item 2');
ListBox1.Items.Add('Item 3');
ListBox1.Items.Add('Item 4');
ListBox1.Items.Add('Item 5');
end;
procedure TForm1.ListBox1DragOver(Sender, Source: TObject; X, y: Integer;
State: TDragState; var Accept: Boolean);
begin
// Accept Listbox as source
Accept:= Source is TListBox;
end;
procedure TForm1.ListBox1DragDrop(Sender, Source: TObject; X, y: Integer);
begin
// Put coordinates in ToPos
ToPos.X:= X;
ToPos.y:= y;
// Check that both sender and source is a ListBox
if (Sender is TListBox) and (Source is TListBox) then
begin
// Get ListBox-item indexes and send them to the MoveItem procedure
MoveItem(ListBox1.ItemAtPos(FromPos, true), ListBox1.ItemAtPos(ToPos,
true));
end;
end;
procedure TForm1.ListBox1MouseDown(Sender: TObject; Button: TMouseButton;
Shift: TShiftState; X, y: Integer);
begin
// Get sourceitem position
FromPos.X:= X;
FromPos.y:= y;
end;
procedure TForm1.MoveItem(FromPos, ToPos: Integer);
var
n: Integer;
DummyList: TStringList;
begin
DummyList:= TStringList.Create;
try
if (FromPos > -1) and (ToPos > -1) then
begin
// Copy listbox to DummyList
DummyList.Text:= ListBox1.Items.Text;
if FromPos > ToPos then
begin
// If item is dragged downwards rearrange the list this way
ListBox1.Items[ToPos]:= ListBox1.Items[FromPos];
for n:= (ToPos + 1) to FromPos do
ListBox1.Items[n]:= DummyList[n - 1];
end
else
begin
// If item is dragged upwards rearrange the list this way
ListBox1.Items[ToPos]:= ListBox1.Items[FromPos];
for n:= (ToPos - 1) downto FromPos do
ListBox1.Items[n]:= DummyList[n + 1];
end;
end;
finally
DummyList.Free;
end;
end;
end.
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