Let them drag and drop files on your program

See Also

• Document Scraps: Save bits and pieces of your files (Windows tip)

• Drag and drop file names to the Command Prompt (Windows tip)

• Drag and view (Windows tip)

• Dragging and dropping objects between full screen applications (Windows tip)

• Explorations shouldn't be limited to remote resources (Internet tip)

• Fastest way to add items to your Start Menu (Windows tip)

If you want to let your users drag and drop files on your program from the File Manager and Windows Explorer, simply add the code inside //>>> and //<<< to your program as in the following example:

unit dropfile;

interface

uses

Windows, Messages, SysUtils, Classes,

Graphics, Controls, Forms, Dialogs;

type

TForm1 = class(TForm)

procedure FormCreate(Sender: TObject);

private

{ Private declarations }

public

{ Public declarations }

//>>>

// declare our DROPFILES message handler

procedure AcceptFiles( var msg : TMessage );

message WM_DROPFILES;

//<<<

end;

var

Form1: TForm1;

implementation

uses

//>>>

//

// this unit contains certain

// functions that we'll be using

//

ShellAPI;

//<<<

{$R *.DFM}

//>>>

procedure TForm1.AcceptFiles( var msg : TMessage );

const

cnMaxFileNameLen = 255;

var

i,

nCount : integer;

acFileName : array [0..cnMaxFileNameLen] of char;

begin

// find out how many files we're accepting

nCount := DragQueryFile( msg.WParam,

$FFFFFFFF,

acFileName,

cnMaxFileNameLen );

// query Windows one at a time for the file name

for i := 0 to nCount-1 do

begin

DragQueryFile( msg.WParam, i,

acFileName, cnMaxFileNameLen );

// do your thing with the acFileName

MessageBox( Handle, acFileName, '', MB_OK );

end;

// let Windows know that you're done

DragFinish( msg.WParam );

end;

//<<<

procedure TForm1.FormCreate(Sender: TObject);

begin

//>>>

//

// tell Windows that you're

// accepting drag and drop files

//

DragAcceptFiles( Handle, True );

//<<<

end;

end.

Listing #1 : Delphi code. Right click dropfile.pas to download.

Now you can drag and drop files on the form that you registered as a recipient of dropped files by calling the "DragAcceptFiles()" function as in the above example.