Adding Multiselection to TFileOpenDialog

Date: 7 February 1997
Author: Brice VIDAL
Platform: 32 bits environment
In memory of: Carcass

Overview

• An advantage of MDI applications is the ability to open several files from a directory at a time. When using a TFileOpenDialog, to enable multiselection you must set the OFN_ALLOWMULTISELECT flag in the TOpenSaveDialog::TData structure passed to the dialog.

• Then starts the real work: decode the filenames. The string returned is kind of formatted: if 1 file has been selected then the full path of the filename is returned, but if several files have been selected then the path is first, followed by each file name. Each item is separated by a null terminator char and the end of the string is delimited by 2 null terminator characters. You can download the code here, it is completely documented so do not hesitate.

Setting the OFN_ALLOWMULTISELECT flag

• Generally this flag is set in the SetupWindow function of your MDI class, although you can define it just before opening the dialog box. All you need is set the flags of the TOpenSaveDialog::TData struct that will be passed to the constructor. Have a look at your help file for available flags.
• If you want an explorer type (common win95 open dialog boxes) dialog box allowing multiselection here's the first step:

#include <owl/opensave.h>

TOpenSaveDialog::TData FileData;

FileData.Flags = OFN_EXPLORER | OFN_ALLOWMULTISELECT; 

Managing the result

Then starts the real work.

• First, we create, call and check the return value of the dialog box: 

#include <dir.h>
#include <cstring.h>

if(TFileOpenDialog(this, FileData).Execute()==ID_OK)
{ 

• Then we need to know how many files have been selected. So we get the current working directory with getcwd() and compare its number of letters to the one of the FileData.FileName string with  strlen() because the strlen function calculates the number of letters until it reaches a null terminator and then returns this number without counting the null terminator. So if the directory's length is the same as the FileData.FileName one it means that several files have been selected.
  
  char currentDirectory[MAXPATH];
  getcwd(curPath, MAXPATH);
  
  int size = strlen(FileData.FileName);
  
  if(strlen(curPath) != size)
      OpenFile();
  else
  {
• The next step is to open each file. For this we create a string containing the directory. A while loop starts until the length of what is behind the null terminator is 0. If there is a file name we collect it and create a string composed of the directory to which we add the file name and then a call to OpenFile()  does all the work.
  
      char* path = FileData.FileName;
      bool exit = false;
   
      string dir(path);        
      dir += "\\";
  
      while(!exit)
      {
          char* file = FileData.FileName + size + 1; // skip the null terminator
          int fileSize = strlen(file);
  
          if(!fileSize)  
              exit = true;
  
          else
          {
              size += (fileSize + 1);
              string openName(file);
              openName = dir + openName;
              OpenFile(openName.c_str());
          }
      }
  }

}

Here's an example of an OpenFile() function:

void OpenFile(const char* fileName = 0)
{
    if(!fileName)
        // the FileData.FileName contains the file name