Adding filters to the Open File dialog

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Introduction

The MFC CFileDialog class only has provision for one default file extension, which is added to a filename if no extension is given. A file export functionality deals with possibly many different file extensions, that have to be added depending on the filetype chosen. The CFileExportDialog class does this. Moreover, when the user selects another filetype from the combobox, the extension in the filename editcontrol is automatically changed.

The usage of the dialog is simple because it mimics the usage of the parent class CFileDialog. Apart from the constructor and destructor, there is only one extra public function, GetFilterIndex(), which returns the index of the selected filetype. This is useful if one extension is shared by two or more filetypes, so the filetype cannot be determined from the resulting filename. In keeping with standard Windows practice, this index starts at 1.

One thing to note is the format of the filter string. This string MUST be of the form "Word File (*.doc)|Text File (*.txt)". I.e. one extension per format, and the formats separated by pipes. Every extension must be put between parentheses and be of the form *.ext.

The initial file type is determined from the default filename, if it is given. This filename may also be "*.ext". If no default filename is given, the first filetype in the filter string is used.

The CFileExportDialog class is typically used like this:

CFileExportDialog dialog("Save As Type", // title
  "Windows Bitmap (*.bmp)|JPEG Compressed Image (*.jpg)|"\  // filter string..
  "Windows Meta File (*.wmf)|Windows Enhanced Meta File (*.emf)", // with file types
  "visualization.jpg"); // default filename (may be omitted)

if (dialog.DoModal() == IDOK) {
  CString filename = dialog.GetPathName();
  int filetype = dialog.GetFilterIndex();
  SaveFile(filename, filetype); // defined somewhere in the application
}

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