QFileSystemModel and QSortFilterProxyModel - root index is not preserved

jsulm · wrote on 28 Jun 2019, 06:30

@MasterBLB "minimal compilable example".
What you provided are some code snippets, nothing one can compile.
It is important to have a minimal example showing the issue, because the issue could be in other parts of the code than what you posted.
Also, if you only post code snippets you're actually asking others to create a minimal compilable example...

SGaist · wrote on 28 Jun 2019, 06:32

Sorry but no it's not.

It's neither minimal nor compilable.

It can't be just copied and pasted in a main.cpp to be built.
There's no main function to launch the application
There's a designer based ui used that is not available
You are using subclasses that are maybe doing something or not so we don't know whether it's in that part that something is going on.

Therefore, you are asking people to write and build themselves that minimal use case to find out whether they can reproduce your issue.

MasterBLB · 28 Jun 2019, 09:21

Well, I was sure Qt Champions are capable of:

creaing a QTreeView instance
creating a QFileSystemModel instance
creating a QSortFilterProxyModel instance
apply a simple filter for the filter model

well then, here is main:

int main(int argc, char *argv[])
{
   QApplication a(argc, argv);
    
   QTreeView treeView;

   QFileSystemModel navigationModel;
    navigationModel.setFilter(QDir::AllDirs | QDir::NoDotAndDotDot | QDir::Files);
    navigationModel.setNameFilterDisables(true);
QString root(/*set it somewhere into directory structure, say C:/Qt/some version*/);
navigationModel.setRootPath(root);

QSortFilterProxyModel filteringModel;
filteringModel.setSourceModel(&navigationModel);
    filteringModel.setRecursiveFilteringEnabled(true);
    filteringModel.setFilterCaseSensitivity(Qt::CaseInsensitive);

    treeView.setModel(&filteringModel);
    treeView.setRootIndex(filteringModel.mapFromSource(navigationModel.index(root)));

filteringModel.setFilterFixedString(/*put some folder name which appears deeper in the choosen root*/);

    treeView.show();

   return a.exec();
}

jsulm · wrote on 28 Jun 2019, 09:21

@MasterBLB said in QFileSystemModel and QSortFilterProxyModel - root index is not preserved:

Well, I was sure Qt Champions are capable of

You're the one asking for help. It is not about whether Qt champions are capable of doing this or not, it's simply about to help others to help you. You're aware that your list means work for others, right? People in this forum are not paid workers who have to work for you, but just volunteers spending their own time to help others...

MasterBLB · wrote on 28 Jun 2019, 09:48

And that's why I've written the example within around 60s, as requested. I hope it fulfills expectations, but if needed feel free to ask about implementation details of models, though as mentioned there isn't anything related to manipulating root index.

mrjj · wrote on 28 Jun 2019, 15:40

Hi
I can confirm it get the same result on Qt5.12.3 and Qt5.9
so at least we can say its not a local bug of sorts.

#include <QApplication>
#include <QFileSystemModel>
#include <QSortFilterProxyModel>
#include <QTreeView>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QTreeView treeView;

    QFileSystemModel navigationModel;
    navigationModel.setFilter(QDir::AllDirs | QDir::NoDotAndDotDot | QDir::Files);
    navigationModel.setNameFilterDisables(true);
    QString root("C:/Qt/5.12.3/msvc2017_64");
    navigationModel.setRootPath(root);

    QSortFilterProxyModel filteringModel;
    filteringModel.setSourceModel(&navigationModel);
    filteringModel.setRecursiveFilteringEnabled(true);
    filteringModel.setFilterCaseSensitivity(Qt::CaseInsensitive);

    treeView.setModel(&filteringModel);
    treeView.setRootIndex(filteringModel.mapFromSource(navigationModel.index(root)));

    filteringModel.setFilterFixedString("Lib");

    treeView.show();

    return a.exec();
}

SGaist · wrote on 28 Jun 2019, 19:01

As @mrjj I can reproduce that on macOS with a recent build of Qt.

You should check the bug report system to see if there's already something related. If not, then please consider opening a new report providing that minimal compilable example.

MasterBLB · 28 Jun 2019, 20:12

Oh crap, tough luck :/ How to open a Qt bug report?

mrjj · wrote on 28 Jun 2019, 20:12

@MasterBLB
Hi
Well you just go there and login with the credentials you use here.
A good read is
https://wiki.qt.io/Reporting_Bugs

MasterBLB · wrote on 2 Jul 2019, 08:47

@mrjj , @SGaist - have you reported the bug? If not I will try when I'll go back home after work.

SGaist · wrote on 2 Jul 2019, 08:51

Personally, I didn't. Since you found it, the honour is yours :)

mrjj · wrote on 2 Jul 2019, 09:03

Hi
nope, if i had made report, i would have linked url here :)
So please do.

VRonin · wrote on 2 Jul 2019, 09:15

I don't think it's a bug.
setRootIndex is a method of the view. The model has no way of knowing (and shouldn't know) what a view is using as root. The filter set on the proxy applies to the whole model. If the index used as root by a view gets filtered out it's only natural for a view to revert to using QModelIndex() as root.

What you need is a proxy model that implements the setRootIndex functionality at the model level. This is on the list of nice-things-I-would-like-to-add-to-Qt-models and it's a fairly easy one to do but I need to find time for it :(

MasterBLB · 2 Jul 2019, 18:41

...and now I'm confused :/

JonB · wrote on 2 Jul 2019, 18:41

@MasterBLB
Confused in what way? I have just read this thread and what @VRonin has written seems correct to me. Are you not understanding what he is saying, or what?

MasterBLB · 3 Jul 2019, 08:01

In the way such behavior breaks SOLID substitute rule - I can't use descendant class QFileSystemModel like it was its base class QAbstractItemModel in QSortFilterProxyModel. While not a 100% bug it's definitely a serious design flaw, and worth to be reported. But where?

jsulm · wrote on 3 Jul 2019, 08:01

@MasterBLB said in QFileSystemModel and QSortFilterProxyModel - root index is not preserved:

But where?

In Qt bug tracker https://bugreports.qt.io/secure/Dashboard.jspa
Also you can talk to Qt developers on their mailing list.

VRonin · 7 Mar 2019, 10:08

breaks SOLID

It doesn't. In fact, if it worked as you expected it would break SOLID

it's definitely a serious design flaw

Sorry to be brutal: No, it's not a flaw, you just didn't understand the design of model/views.
To help you get a better idea of what is going on, try use the same model with 2 different treeviews. In only one of the view call setRootIndex, and then trigger the filtering.

Brad1111 · wrote on 12 Feb 2025, 22:50

Im actually encountering the very same issue.
Clearly it wont be fixed by Qt since Ive even seen posts about this issue back from 2011.
Could someone help me a little bit by telling me what to do please ?

@VRonin You were the most precise, suggesting to implements the setRootIndex to the proxymodel, but I would still require a bit more info if I am to do it on my own please :D

jeremy_k · 13 Feb 2025, 04:28

It looks like @VRonin implemented his idea. See https://github.com/VSRonin/QtModelUtilities/blob/master/READMERootIndexProxyModel.md