QAbstractFileEngineIterator Class Reference

Detailed Description

The QAbstractFileEngineIterator class provides an iterator interface for custom file engines.

If all you want is to iterate over entries in a directory, see QDirIterator instead. This class is only for custom file engine authors.

QAbstractFileEngineIterator is a unidirectional single-use virtual iterator that plugs into QDirIterator, providing transparent proxy iteration for custom file engines.

You can subclass QAbstractFileEngineIterator to provide an iterator when writing your own file engine. To plug the iterator into your file system, you simply return an instance of this subclass from a reimplementation of QAbstractFileEngine::beginEntryList().

Example:

 QAbstractFileEngineIterator *
 CustomFileEngine::beginEntryList(QDir::Filters filters, const QStringList &filterNames)
 {
     return new CustomFileEngineIterator(filters, filterNames);
 }

QAbstractFileEngineIterator is associated with a path, name filters, and entry filters. The path is the directory that the iterator lists entries in. The name filters and entry filters are provided for file engines that can optimize directory listing at the iterator level (e.g., network file systems that need to minimize network traffic), but they can also be ignored by the iterator subclass; QAbstractFileEngineIterator already provides the required filtering logics in the matchesFilters() function. You can call dirName() to get the directory name, nameFilters() to get a stringlist of name filters, and filters() to get the entry filters.

The pure virtual function hasNext() returns true if the current directory has at least one more entry (i.e., the directory name is valid and accessible, and we have not reached the end of the entry list), and false otherwise. Reimplement next() to seek to the next entry.

The pure virtual function currentFileName() returns the name of the current entry without advancing the iterator. The currentFilePath() function is provided for convenience; it returns the full path of the current entry.

Here is an example of how to implement an iterator that returns each of three fixed entries in sequence.

 class CustomIterator : public QAbstractFileEngineIterator
 {
 public:
     CustomIterator(const QStringList &nameFilters, QDir::Filters filters)
         : QAbstractFileEngineIterator(nameFilters, filters), index(0)
     {
         // In a real iterator, these entries are fetched from the
         // file system based on the value of path().
         entries << "entry1" << "entry2" << "entry3";
     }

     bool hasNext() const
     {
         return index < entries.size() - 1;
     }

     QString next()
     {
        if (!hasNext())
            return QString();
        ++index;
        return currentFilePath();
     }

     QString currentFileName()
     {
         return entries.at(index);
     }

 private:
     QStringList entries;
     int index;
 };

Note: QAbstractFileEngineIterator does not deal with QDir::IteratorFlags; it simply returns entries for a single directory.