WTL File Dialog Filter String

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• Download demo project - 13 Kb

Introduction

One neat feature that MFC supports is the ability to store filter strings for use with the CFileDialog in the applications stringtable. The reason special support exists for this is because the OPENFILENAME struct (used by the CFileDialog) expects the filter string components to be delimited using '\0' chars, for example:

Text Files (*.txt)\0*.txt\0All Files (*.*)\0*.*\0

Unfortunately, you can't embed strings containing \0 in your applications string table, so in MFC a pipe symbol is used instead, e.g.:

Text Files (*.txt)|*.txt|All Files (*.*)|*.*|

So, in order to allow strings in this format to be used with WTL applications, you can now use the CFileDialogFilter class. To use the class, first include the header file:

#include "filedialogfilter.h"

Next, simply create a CFileDialogFilter object, passing the ID of the resource string - and then pass it as the lpszFilter parameter to the WTL CFileDialog:

CFileDialogFilter strFilter(IDS_FILTER);
CFileDialog dlg(TRUE, NULL, NULL, OFN_HIDEREADONLY|OFN_OVERWRITEPROMPT, 
    strFilter);
// Display
dlg.DoModal();

That's it! The class will automatically load the string and replace any '|' chars with '\0' chars.

CFileDialogFilter

// Implementation of the CFileDialogFilter class.
#pragma once

#include <atlmisc.h>

// Class to support a filter list when using the WTL CFileDialog.
// Allows a filter string delimited with a pipe to be used 
// (instead of a string
// delimited with '\0')
class CFileDialogFilter  
{
private:
    CString m_strFilter;
public:
    CFileDialogFilter()
    {
    }

    /// nID The ID of a resource string containing the filter
    CFileDialogFilter(UINT nID)
    {
        SetFilter(nID);
    }
    
    /// lpsz The filter string
    CFileDialogFilter(LPCTSTR lpsz)
    {
        SetFilter(lpsz);
    }
    
    ~CFileDialogFilter()
    {
    }

    inline LPCTSTR GetFilter() const { return m_strFilter; }
    inline operator LPCTSTR() const { return m_strFilter; }

    // Set the filter string to use
    // nID - The ID of a resource string containing the filter
    void SetFilter(UINT nID)
    {
        if (m_strFilter.LoadString(nID) && !m_strFilter.IsEmpty())
            ModifyString();
    }

    // Set the filter string to use
    // lpsz - The filter string
    void SetFilter(LPCTSTR lpsz)
    {        
        m_strFilter = lpsz;
        if (!m_strFilter.IsEmpty())
            ModifyString();
    }
private:
    // Replace '|' with '\0'
    void ModifyString(void)
    {
        // Get a pointer to the string buffer
        LPTSTR psz = m_strFilter.GetBuffer(0);
        // Replace '|' with '\0'
        while ((psz = _tcschr(psz, '|')) != NULL)
            *psz++ = '\0';
    }
};

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