QFileSystemModel and QSortFilterProxyModel - root index is not preserved

[mrjj]

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]

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]

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

[mrjj]

@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]

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

[SGaist]

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

[mrjj]

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

[VRonin]

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]

...and now I'm confused :/

[JonB]

@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]

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]

@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]

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]

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]

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

[Brad1111]

@jeremy_k Wow, Awesome ! Thanks for your answer and massive props to @VRonin !