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Frequently Asked Questions

Drag and Drop with Files

Question:

How do I accept files that are dropped on my application?

Answer:

You must interface with the Windows Shell API module to let
Windows know that your application accepts dropped files (this
can be done in your main form's create event), and then you must
respond to the drag events as they happen by creating an event
handler.

The following is an example of a Delphi form that accepts dropped
files and adds the names of the files to a memo component:

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    Memo1: TMemo;
    procedure FormCreate(Sender: TObject);
  private
    procedure WMDROPFILES(var Message: TWMDROPFILES);
      message WM_DROPFILES;
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

uses ShellApi;

procedure TForm1.FormCreate(Sender: TObject);
begin
 {Let Windows know we accept dropped files}
  DragAcceptFiles(Form1.Handle, True);
end;

procedure TForm1.WMDROPFILES(var Message: TWMDROPFILES);
var
  NumFiles : longint;
  i : longint;
  buffer : array[0..255] of char;
begin
 {How many files are being dropped}
  NumFiles := DragQueryFile(Message.Drop,
                            -1,
                            nil,
                            0);
 {Accept the dropped files}
  for i := 0 to (NumFiles - 1) do begin
    DragQueryFile(Message.Drop,
                  i,
                  @buffer,
                  sizeof(buffer));
    Form1.Memo1.Lines.Add(buffer);
  end;
end;

end.

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