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Posted 4 Jan 2013


, 4 Jan 2013
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Multiselect file / folder dialog.


All works fine until you find yourself before the task to have a dialog which allows selection of multiple files and folders in one go. Often this is the case when it comes to batch processing. Of course, I have heard about tricks and tweaks like entering “File folder” or some stuff as the filename before starting a dialog. I got sick and tired of it all.

Honestly this class did not experience extensive testing, does not support selecting the nearest entry by pressing a key (the leading character of the entry), nor is drag & drop implemented. It might thus undergo minor changes in the future. The deal is that I don’t want to follow up major postings about this, that and god knows what. So, if you feel change is needed, go ahead and serve yourself. (Expect plenty of source code in an unusual dense writing style). What it offers is usability on several platforms since the dialog is a rewrite from scratch and rarely seen simplicity. The Windows 7 Explorer and the Vista FileOpenDialog where looked at during development. Worst case you will deal a bit with assignments of known folders e.g.


but not under Windows 7.

A dialog?

Well it has a dialog functionality but only two items are accessible before a call to ShowDialog(). It is not visible in the designer either (it does not contain components), so don’t put it in the toolbox. Not much? No, it does not need more! Memory is assigned during the execution of the dialog and released when exiting. Most properties and functions are declared private. Lots of information is read out from the registry like: Places previously visited, previous selections and associated data. The dialog will not make any entries in the registry. Support for skins was not a requirement. Perhaps the start folder (initialPath) could be assigned as well. To save execution time and memory only the folder level below the shown level is read to indicate possible subfolders. This resembles lazy loading a bit.


Shown main folders                Read subfolders
C:\                               The root of c:\ only
D:\                               The root of d:\ only
C:\Windows                        The fist level subfolders of c:\Windows

Be sure that OpenFileFolder.dll, shell32.dll version 5 and above, and AnswerBox.dll from a previous article is in the directory of execution. Ensure that shell.dll and OpenFileFolder.dll are entered in the project References (see Prerequisites). OpenFileFolder is internally makes use of answerbox.dll.

Coding, here we go:

using OpenFileFolders;
OpenFileFolder off = new OpenFileFolder();
// Following 4 lines are not mandatory!
off.FilterComboBox.Items.Add("All files (*.*)");
off.FilterComboBox.Items.Add("Exe Files (*.exe)");
off.FilterComboBox.SelectedIndex = 0;
off.initialPath = @"D:\Icons\_BMP";
DialogResult z = off.ShowDialog();
string seletedItems = off.FileName;

That’s it already. If something was selected in the dialog, the seletedItems will not be an empty string (null) and

is set to DialogResult.OK and not null either.

In case multiple items have been selected, seletedItems will show something like:

D:\\Icons\\_png\\3D (2).png;D:\\Icons\\_png\\3D (3).png;D:\\Icons\\_png\\3D (4).png

Arbitrate the information which is delimited with a semicolon to get the individual selections.

Changing face:

The project is split up in two parts (two folders). The actual development of the dialog is found in OpenFileFolder. The whole development took place in that folder. Tested code was then copied over into the files found in OpenFileFolderClass. This might be a bit an unusual approach but guaranties clear separation of targets and serves as a backup as well. In times of challenge, a save heaven. Do not expect files to be identical in the two folders. The first folder contains files which supports the Design Editor the files in the second folder draw the whole GUI using code.


In the directory of execution:

  • shell32.dll: Version 5 and above.  Date >= 2009
  • AnswerBox.dll: From a previous article


There is absolute no warranty what so ever implied or assumed. Use it at your own risk. It does a marvelous job for the author. Copyrights and Trademarks shall belong to their respective owners. I am not going to fight over that!


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Philippines Philippines
Grew up in a metal processing company and did industrial HW/SW development since the birth of Intel’s 8080. Lectured IT since 1986 at several levels. Hobbies, sidesteps: Woodworking and deep sea diving. Background: ASM, C, C++. Platforms: Win, Novel, CP/M, MP/M, DOS, (Linux).

It’s not the developer’s duty to pay up for the engineer’s ignorance.

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Comments and Discussions

GeneralUpdated code including Bugfixes Pin
cyprussun12-Mar-13 20:03
membercyprussun12-Mar-13 20:03 

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