Drag-and-drop-from-filemanager


            You need to use these 3 functions from the ShellApi:
DragAcceptFiles - registers whether a window accepts dropped files 
DragQueryFile - retrieves the filename of a dropped file 
DragFinish - releases memory allocated for dropping files 
 
 uses
 ShellApi;
 
..
 
procedure TForm1.FormCreate(Sender: TObject);
begin
 DragAcceptFiles(Form1.Handle, true);
 Application.OnMessage := AppMessage;
end;
{ message handler procedure }
// Delphi 1: type DWord = longint; .. FileIndex := -1;
procedure TForm1.AppMessage(var Msg: Tmsg; var Handled: Boolean);
const
 BufferLength : DWORD = 511;
var
 DroppedFilename : string;
 FileIndex : DWORD;
 NumDroppedFiles : DWORD;
 pDroppedFilename : array [ ..511] of Char;
 DroppedFileLength : DWORD;
begin
 if Msg.message = WM_DROPFILES then
 begin
 FileIndex := $FFFFFFFF;
 NumDroppedFiles := DragQueryFile(Msg.WParam, FileIndex,
 pDroppedFilename, BufferLength);
 for FileIndex := 0 to (NumDroppedFiles - 1) do
 begin
 DroppedFileLength := DragQueryFile(Msg.WParam, FileIndex,
 pDroppedFilename,
 BufferLength);
 DroppedFilename := StrPas(pDroppedFilename);
 { process the file name you just received }
 end;
 DragFinish(Msg.WParam); { important to free memory }
 Handled := true;
 end;
end; 
 
Notes:
When dropping files, the DroppedFilename is the complete path, not just the filename.ext 
It is possible to drag and drop just a directory. So if you are expecting filenames, you have to check for existence yourself. 
The filenames come in uppercased.
Examples Delphi
