Get QModelIndex in delegate

  • Hi,

    I have the following problem: I have a TreeView of a QFileSystemModel

        TreeView {
            id: view
            anchors.fill: parent
            sortIndicatorVisible: true
            model: fileSystemModel
            rootIndex: rootPathIndex
            selection: sel

    and a custom delegate which adds a CheckBox next to the filename. I would like to store information about whether an element has been checked in my model, so that after sorting the name column still the right boxes are checked (very similar to this TreeView of QFileSystemModel: Remember selection after sorting. However, I have the problem that the solution in the linked post works as the ItemSelectionModel is returning a list of QModelIndex and if I want to do something similar, by adding a appendChecked invokable function to my model and call it in the delegate

            Component {
                id: mycomp
                Item {
                    id: myitm
                        id: myrow
                            id: cbox
                            property bool checked: false
                            anchors.baseline: ctext.baseline
                            onCheckedChanged: {
                                if(checked==false) {

    model.index seems to only give me the row number of the delegate and not a QModelIndex. But i would need to store a QPersistentModelIndex in my model. How can I get the QModelIndex in a delegate and not just the row number?

  • typeof(model.index) gives number

  • Qt Champions 2018

    In general, this is very easy as Qt already has a role to save the CheckboxState (Qt::CheckStateRole) so you just need the last part of this wiki article to read/write that role

    The problem here is that QFileSystemModel can't handle Qt::CheckStateRole.
    To overcome this problem you need a proxymodel between your model and the view that takes care of the roles that QFileSystemModel doesn't manage.

    I worked on such a solution in my spare time and, while I can't guarantee 100% stability you can find it here under the name RoleMaskProxyModel. I haven't developed examples for it yet but the test method tst_RoleMaskProxyModel::testUseRoleMask should give you an idea of the usage

  • Adding a role to QFileSystemModel should also not be difficult. However, to set the initial state I guess I must once walk through the whole model, right? Or can one set a default state for a role?

  • Qt Champions 2018

    @maxwell31 said in Get QModelIndex in delegate:

    Adding a role to QFileSystemModel should also not be difficult.

    It's not only if you either use the privates of Qt or recompile a custom Qt widgets model

    However, to set the initial state I guess I must once walk through the whole model, right?

    Normally yes

    Or can one set a default state for a role?

    You could in the subclass but in this case it is probably easier to handle the default state directly in the delegate

  • Hm, so no easy solution :-(

  • What about getting the QModelIndex inside the delegate, that would be easy if possible

  • Actually I found how to get the index:


    where filesystemmodel is

     engine.rootContext()->setContextProperty("fileSystemModel", fsm);

    and fsm the QFileSystemModel

  • Now I would only need to find out how to set a property of my TableViewColumn delegate, e.g. for the onSortIndicatorChanged signal of my view.

    I have a isChecked(QModelIndex) function in my model. If I can loop over the displayed delegates, I could update their checked state, but I don't know how to do this

    Edit: Hm, fileSystemModel.index(model.urlstringrole,0) seems to give the wrong index

  • Qt Champions 2018

    What you are doing is flaky at best. Please read that wiki page I linked especially in the section "Using the data in QML"

  • :-) Yes, I have the feeling that it is flaky at best. But is there really no way to get the QModelIndex right? I found that using a Connection to the delegate should work, but my problem is still getting the right QModelIndex for a delegate

  • Is there something like a


    function accessible?

  • As I do not yet understand the solution @VRonin has in his repository, I thought about a hacky solution:

    Keep a list of persistent model indexes in a QFileSystemModel derived model, add a IsChecked Role to the derived model and set the data function for this role to

            case IsCheckedRole:
                return isChecked(QPersistentModelIndex(index));

    a custom function, which will check, whether index is in the persistentModel Index list.

    This brought to my mind, that I don't actually know how this works. If in the delegate I then use this role to set the checked property of a checkbox, how does the delegate now if the model is updated? It seems to work though - but not completly:

    If I select an item, sort by the name column, deselect it and sort again, the item is selected again. I guess this has nothing todo with my isChecked function. A similar thing is if I only add a checkbox to the delegate and do nothing in the model. If I select it, and then sort, the item which goes to its place due to sorting is selected.

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