How to override (re-implement) a member function in QFileSystemModel

Question

I\'ve been struggling with this for a while.

Qt\'s QFileSystemModel is really slow when fetching several hundred files because of a really bad icon fetc

Answer 1

If a function in a base class is virtual then it is virtual in derived classes as well. The following will print "C":

#include <iostream>

class A {
public:
  virtual void data() = 0;
};

class B: public A {
public:
  void data() { std::cout << "B\n"; }
};

class C: public B {
public:
  void data() { std::cout << "C\n"; }
};

int
main() {
  C c;
  A *a = &c;
  a->data();

  return 0;
}

QFileSystemDialog is derived from QAbstractItemModel in which data() is pure virtual. You couldn't even instatiate the former if it didn't override data() with its own implementation.

See http://qt-project.org/doc/qt-4.8/qabstractitemmodel.html#data

Answer 2

Looks like this was anticipated, as there is a method for setting the "icon provider":

http://doc.qt.io/archives/qt-4.7/qfilesystemmodel.html#setIconProvider

The parameter, a QFileIconProvider, looks to be a fairly simple class that you can implement an instance of yourself, with a method that fetches an icon from a QFileInfo (basically, a file name):

http://doc.qt.io/archives/qt-4.7/qfileinfo.html

You could implement one of these that just returns the same icon for everything. If you find that doesn't address your problem, the following compiled fine for me...FWIW:

class FileModel : public QFileSystemModel {
public:
    QVariant data(const QModelIndex &index, int role) const
    {
        if (role == Qt::DecorationRole) {
            return QVariant (QIcon ());
        }    

        return QFileSystemModel::data(index, role);
    }
};