QML Repeater delegates display correctly but C++ ViewModel getWord() returns incomplete empty — what am I missing?

Question

I’m working on a QUL / Qt Quick Ultralite application (targeting ESP32, using QUL 2.9.0) where I have:

A CharacterSelectors.qml component that uses a Repeater to render multiple character-selector subcomponents.
A TextEditVM (C++ / QUL view-model) with getWord() method, which is supposed to concatenate the currently selected characters from each CharacterSelector. and a setter setChar(int index, const std::string& data)
From the logs (via idf.py monitor), I see that when I select individual characters, those delegate components are created and some logging occurs. However, when I call getWord() from the VM, the returned word is incomplete (often empty).

Below are simplified / trimmed but representative versions of my .qml and C++ VM code. I hope someone can spot what I’m doing wrong or suggest a better pattern.

CharacterSelectors.qml

import QtQuick 2.15
import QtQuick.Controls 2.15
import Constants 1.0
import "../BaseControl"

Row {
  id: root
  spacing: 10
  
  property string currentWord: ""
  
  TextEditVM {
    id: textEditVM
    Component.onCompleted: {
      textEditVM.init(5)
    }
  }

  Repeater {
    id: repeater
    model: 5
    CharacterSelector {
      property int index: 0
      property string chararcter: " "

      onSelectedCharChanged: {
        chararcter = selectedChar;

        if (selectedChar !== "") {
          console.log("CharacterSelectors - Setting char at index", index, "to", selectedChar)
          textEditVM.setChar(index, selectedChar)
          // Force update the currentWord property
          root.currentWord = textEditVM.getWord()
        }
      }
    }
  }

  function getWord() : string {
    return textEditVM.getWord();
  }
}

(There is also some parent QML or C++ code that instantiates CharacterSelectors, passes textEditVM as vm, etc.)

TextEditVM (C++ / QUL side)

text_edit_vm.h

#pragma once
#include <QObject>
#include <QString>
#include <vector>

class TextEditVM : public QObject {
    Q_OBJECT
    Q_PROPERTY(QString word READ getWord WRITE setWord NOTIFY wordChanged)
public:
    explicit TextEditVM(QObject *parent = nullptr);

    QString getWord() const;
    void setWord(const QString &w);

signals:
    void wordChanged();

private:
    QString m_word;
};

text_edit_vm.cpp

#include "text_edit_vm.h"
#include <QDebug>

TextEditVM::TextEditVM(QObject *parent) : QObject(parent), m_word("") {
    qDebug() << "TextEditVM initialized";
}

QString TextEditVM::getWord() const {
    qDebug() << "TextEditVM::getWord returning:" << m_word;
    return m_word;
}

void TextEditVM::setWord(const QString &w) {
    if (m_word != w) {
        m_word = w;
        qDebug() << "TextEditVM::setWord, new word =" << m_word;
        emit wordChanged();
    }
}

getWord() from the view model never runs (or returns empty) even though setChar() logs show the character was set. What am I missing? Is this a timing / delegate-creation issue, a problem exposing the C++ object to QML, or a QUL-specific string/notify issue?

As the characterselectors changed characters, they should be visible on the textdialog. But it didn't

textEditVM does not have a setChar method, only a setWord method. — Atmo
– Atmo, Commented Sep 28 at 19:37
If I'm not mistaken, the documentation shows that defining QML properties on QUL is very different from desktop C++/QML integration. — smr
– smr, Commented Sep 28 at 23:12
If you want getWord() / setWord() methods accessible from QML, you should make them public and add Q_INVOKABLE, else the only way you can access them is via the Q_PROPERTY, but, I cannot see any evidence that you're using the Q_PROPERTY. — Stephen Quan
– Stephen Quan, Commented Sep 29 at 21:12

JayEff · Accepted Answer · 2025-09-26 12:58:48Z

2

To read the content of m_word in QML, you can use the Q_PROPERTY you defined, by simply doing

  function getWord() : string {
    return textEditVM.word;
  }

You can use this just like you would any other property in qml. Internally, this will use your defined getter function getWord in c++, which you're declaring with the READ keyword in the Q_PROPERTY statement. You can also assign a new value to the property which will call the setter for you.

If you want to be able to call the cpp function getWord directly, you should mark it with Q_INVOKABLE:

Q_INVOKABLE QString getWord() const;

The same goes for the setter which you are also calling in your QML code. Hope this helps.

answered Sep 26 at 12:58

JayEff

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3 Comments

Ron Joshua Quirap Sep 28 at 6:26

The problem I get is that on QUL 2.9.0 that we are currently using for this project does not support Q_INVOKABLE and Q_PROPERTY on the C++ side

Ron Joshua Quirap Sep 28 at 6:54

the vm runs fine when called on the repeater but tried to when it's time to call the getWord function from the text_edit_vm. It seems not being run. As you can see on the text dialog, it didn't get updated...but initially when I hardcoded the getWord from the view model to return a string it will be updated.

JayEff Oct 10 at 14:21

This documentation for Qt for MCUs 2.9.1 seems to indicate that your TextEditVM has to derive from Qul::Object, not QObject: doc.qt.io/archives/QtForMCUs-2.9/qtul-integratecppqml.html and properties are declared differently. Does this also apply to 2.9.0?

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