Get QModelIndex in delegate

maxwell31

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
                Row{
                    id: myrow
                    CheckBox{
                        id: cbox
                        property bool checked: false
                        anchors.baseline: ctext.baseline
                        onCheckedChanged: {
                            if(checked==false) {
                                model.appendChecked((model.index))

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?

maxwell31

typeof(model.index) gives number

VRonin

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

maxwell31

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?

VRonin

@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

maxwell31

Hm, so no easy solution :-(

maxwell31

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

maxwell31

Actually I found how to get the index:

  fileSystemModel.index(model.urlstringrole,0)

where filesystemmodel is

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

and fsm the QFileSystemModel

maxwell31

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

VRonin

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

maxwell31

:-) 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

maxwell31

Is there something like a

  modelAdaptor.mapRowToModelIndex

function accessible?

maxwell31

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.