Drag and Drop files from your application to Windows Explorer in delphi

Drag and Drop files from your application to Windows Explorer in delphi

// Drag and Drop files from your application to Windows Explorer

// ——————————————— //
(*
This example will show you how your application
will be able to copy files from your application to
Windows Explorer using Drag’n Drop.
Exactly the way it is done by the OS itself!

Create a new application containing just one unit,
called ‘Unit1’. Drop a FileListBox and a DirectoryListBox on to the form,
leave their names the way they are.
Connect FileListBox1 with DirectoryListBox1 by setting the FileList-property of
DirectoryListBox1. Make sure that the MultiSelect-property of FileListBox1 is set to ‘True’!

The best thing you can do now is to replace all text with the code below:
// *)
// ——————————————— //

unit Unit1;

interface

uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms,
Dialogs,
StdCtrls, FileCtrl, ActiveX, ShlObj, ComObj;

type
TForm1 = class(TForm, IDropSource)
FileListBox1: TFileListBox;
DirectoryListBox1: TDirectoryListBox;
procedure FileListBox1MouseDown(Sender: TObject; Button:
TMouseButton;
Shift: TShiftState; X, Y: Integer);
procedure FileListBox1MouseMove(Sender: TObject; Shift: TShiftState;
X,
Y: Integer);
private
FDragStartPos: TPoint;
function QueryContinueDrag(fEscapePressed: BOOL;
grfKeyState: Longint): HResult; stdcall;
function GiveFeedback(dwEffect: Longint): HResult; stdcall;
public
end;

var
Form1: TForm1;

implementation

{$R *.DFM}

function GetFileListDataObject(const Directory: string; Files:
TStrings):
IDataObject;
type
PArrayOfPItemIDList = ^TArrayOfPItemIDList;
TArrayOfPItemIDList = array[0..0] of PItemIDList;
var
Malloc: IMalloc;
Root: IShellFolder;
FolderPidl: PItemIDList;
Folder: IShellFolder;
p: PArrayOfPItemIDList;
chEaten: ULONG;
dwAttributes: ULONG;
FileCount: Integer;
i: Integer;
begin
Result := nil;
if Files.Count = 0 then
Exit;
OleCheck(SHGetMalloc(Malloc));
OleCheck(SHGetDesktopFolder(Root));
OleCheck(Root.ParseDisplayName(0, nil,
PWideChar(WideString(Directory)),
chEaten, FolderPidl, dwAttributes));
try
OleCheck(Root.BindToObject(FolderPidl, nil, IShellFolder,
Pointer(Folder)));
FileCount := Files.Count;
p := AllocMem(SizeOf(PItemIDList) * FileCount);
try
for i := 0 to FileCount – 1 do
begin
OleCheck(Folder.ParseDisplayName(0, nil,
PWideChar(WideString(Files[i])), chEaten, p^[i],
dwAttributes));
end;
OleCheck(Folder.GetUIObjectOf(0, FileCount, p^[0], IDataObject,
nil,
Pointer(Result)));
finally
for i := 0 to FileCount – 1 do begin
if p^[i] <> nil then Malloc.Free(p^[i]);
end;
FreeMem(p);
end;
finally
Malloc.Free(FolderPidl);
end;
end;

function TForm1.QueryContinueDrag(fEscapePressed: BOOL;
grfKeyState: Longint): HResult; stdcall;
begin
if fEscapePressed or (grfKeyState and MK_RBUTTON = MK_RBUTTON) then
begin
Result := DRAGDROP_S_CANCEL
end else if grfKeyState and MK_LBUTTON = 0 then
begin
Result := DRAGDROP_S_DROP
end else
begin
Result := S_OK;
end;
end;

function TForm1.GiveFeedback(dwEffect: Longint): HResult; stdcall;
begin
Result := DRAGDROP_S_USEDEFAULTCURSORS;
end;

procedure TForm1.FileListBox1MouseDown(Sender: TObject;
Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
begin
if Button = mbLeft then
begin
FDragStartPos.x := X;
FDragStartPos.y := Y;
end;
end;

procedure TForm1.FileListBox1MouseMove(Sender: TObject; Shift:
TShiftState;
X, Y: Integer);
const
Threshold = 5;
var
SelFileList: TStrings;
i: Integer;
DataObject: IDataObject;
Effect: DWORD;
begin
with Sender as TFileListBox do
begin
if (SelCount > 0) and (csLButtonDown in ControlState)
and ((Abs(X – FDragStartPos.x) >= Threshold)
or (Abs(Y – FDragStartPos.y) >= Threshold)) then
begin
Perform(WM_LBUTTONUP, 0, MakeLong(X, Y));
SelFileList := TStringList.Create;
try
SelFileList.Capacity := SelCount;
for i := 0 to Items.Count – 1 do
if Selected[i] then SelFileList.Add(Items[i]);
DataObject := GetFileListDataObject(Directory, SelFileList);
finally
SelFileList.Free;
end;
Effect := DROPEFFECT_NONE;
DoDragDrop(DataObject, Self, DROPEFFECT_COPY, Effect);
end;
end;
end;

initialization
OleInitialize(nil);
finalization
OleUninitialize;
end.

// ——————————————————————— //
{
As you might have seen, TForm1 is not only a member of class TForm,
but also of class IDropSource!

Now make sure that the two FileListBox events
‘OnMouseMove’ and ‘OnMouseDown’ are set correctly.

Run your application and try out the Drag and Drop feature!
You can select multiple items to drag and press escape to cancel.
The cursor will show you what action will take place.
}