@sierdzio Oh, Do you mean that the QML calls the C++ QAbstractItemModel methods for processing?

I don't know your code structure. My assumption was that you are using QAbstractItemModel and your radio button state is controlled by CheckStateRole.

If, on the other hand, you are using some different mechanism, you need to adapt to that. But definitely, regardless of the mechanism - changing a state (any kind of state - item name, check state, color etc.) is a job of the model (or underlying data), not the view.

@sierdzio Thank you for your question and answer.

What method can I use to traverse the children under the selected node in QML?

Don't do it unless you have to - it's too error prone with delegates coming in and out of existence all the time.

Do I need to add methods to the QAbstractItemModel in C++ ?

MouseArea{
    OnPressed:{
             //...
             if(styleData.depth === 1)
             {
                      var curIndex = treeView.indexAt(mouse.x,mouse.y)
             }
    }
}

Move your MouseArea into the delegate - this way you don't have to find which index and item is affected, because pressed signal will be emitted and handled directly in the item which was clicked.

What method can I use to traverse the children under the selected node in QML?
Do I need to add methods to the QAbstractItemModel in C++ ?

MouseArea{
    OnPressed:{
             //...
             if(styleData.depth === 1)
             {
                      var curIndex = treeView.indexAt(mouse.x,mouse.y)
             }
    }
}

Do this to get rid of the warning:

text: styleData === undefined? "" : styleData.value.name

(and please, please: paste text not pictures where you want to show code! It's much easier for me to then copy-paste your code and show tweaks or corrections)