[ Drag & Drop Of Files ]

Open the Windows Explorer, pick a HTML file, drag it into the Netscape browser and.. what happens? The file will be opened. If you want to do the same with your application then you're right here. I will show you how to do this using a dialog based MFC project.

First thing to do is to make your main window accepts dragged and dropped files. In a dialog based project, this is done best in CYourDialog::OnInitDialog(). Here's the code:

BOOL CYourDialog::OnInitDialog()
{
  //Other things that are done.....
  //..
  //..
 
  //App is now ready for dragged files..
  DragAcceptFiles();
 
  return TRUE;
}

If you want to do this in a SDI/MDI project use CMainFrame::OnCreate(..). Next thing to do is to handle the Window message WM_DROPFILES. In VC++, right click on the window class - dialog or the SDI/MDI mainwindow - and click on something like Add Window Message Handler.

We will you use the following function to get info about the dropped files:

UINT DragQueryFile(HDROP hDrop, UINT  iFile, LPTSTR lpszFile, UINT cch );

• hDrop: information about this "Drop-action". Parameter of WM_DROPFILES.
• iFile: index of the file that should be stored in lpszFile. 0 is the first file, 1 the second.. If iFile is 0xFFFFFFFF, the number of dragged files will be returned.
• lpszFile: pointer to a char-array that will hold the file specified by iFile.
• cch: Size of the char-buffer lpszFile.

An example in action: All files dragged to your diaog box will be opened:

void CYourDialog::OnDropFiles(HDROP dropInfo)
{
   //char-Array that holds the filename
   char buffer[512];
   //Get Count of dragged files
   int count = DragQueryFile(hDrop,0xFFFFFFFF,0,0);
  
   //Enumerate throught dragged files and open
   //one after another (you can also do many other things with them;)
   for (int i = 0; i < count; i += 1)
   {
      //Store the current file in buffer
      DragQueryFile(dropInfo,i,buffer,512);
    
      //Call userdefined function Open(..) with the current file
      Open(buffer);
   }
}

That's it! There isn't much to comment about this code. It's really easy to do that. However if you have problems or questions, m@il me. Happy Coding!