Pass a Playlist from C++ to QML (error Unable to assign [undefined] to ::QDeclarativeAudio*)

davidino

Goodmorning to all,
Qt version 5.12, in a cross compiled environment for raspberrypi using b2qt.
I'm trying to make a music Player where I search for songs in system folders, save them in playlists and make them available as model for view. Then in QML I would select the playlist and load it in MediaPlayer.
Here the code:

PlaylistModel.h

#ifndef PLAYLISTMODEL_H
#define PLAYLISTMODEL_H

#include <QAbstractListModel>
#include <QHash>
#include <QDir>
#include <vector>
#include <memory>
#include <QtMultimedia/QMediaPlaylist>

#include "myplaylist.h"

#include "playListModel_global.h"

class PLAYLISTMODEL_EXPORT PlayListModel : public QAbstractListModel
{
    Q_OBJECT
public:

    enum PlaylistRoles {
        IndexRole = Qt::UserRole + 1,
        IconRole,
        PlaybackRole,
        NextRole,
        PreviousRole,
        SizeRole,
        NameRole
    };

    PlayListModel(QDir dirPath, QObject* parent = nullptr);
    PlayListModel(QString dirPath, QObject* parent = nullptr);

    QStringList playListNames();
    Q_INVOKABLE QMediaPlaylist& getPlaylistFromIndex(int index);

    // QAbstractItemModel interface
    int rowCount(const QModelIndex &parent = QModelIndex()) const override;
    QVariant data(const QModelIndex &index = QModelIndex(), int role = Qt::DisplayRole) const override;
    bool setData(const QModelIndex& index, const QVariant& value, int role = Qt::DisplayRole) override;
    QHash<int, QByteArray> roleNames() const override;

private:
    bool isIndexValid(const QModelIndex& index) const;

    std::vector<std::unique_ptr<myPlaylist>> mPlayListsList;
};

#endif // PLAYLISTMODEL_H

PlaylistModel.c

#include "playlistmodel.h"
#include "playlistmodel.h"

#include <QDirIterator>
#include <QMediaContent>
#include <QImage>

PlayListModel::PlayListModel(QString dirPath, QObject* parent) :
    PlayListModel(QDir(dirPath), parent)
{}

QStringList PlayListModel::playListNames()
{
    QStringList lista;
    for(int i=0; i<rowCount(); i++)
    {
        myPlaylist& newPlaylist = *mPlayListsList.at(static_cast<unsigned int>(i));
        lista.append(newPlaylist.getPlaylistName());
    }
    return lista;
}

PlayListModel::PlayListModel(QDir dirPath, QObject* parent) :
    QAbstractListModel(parent)
{
    QDirIterator it(dirPath.path(), QDirIterator::Subdirectories);
    while (it.hasNext()) {
        if (QFileInfo(it.filePath()).isDir() & (it.fileName()!=".") & (it.fileName()!=".."))
        {
            bool songFound=false;
            QDir dir(it.filePath());
            qDebug()<<"Analizying folder: "<<it.filePath();
            std::unique_ptr<myPlaylist> newPlaylist(new myPlaylist());
            newPlaylist->setPlaylistName(it.fileName());

            QDirIterator song(dir.path(), QDir::Files);
            while(song.hasNext())
            {
                qDebug()<<"Analizying file: "<<song.filePath();
                if((QFileInfo(song.filePath()).suffix() == "mp3") |
                    (QFileInfo(song.filePath()).suffix() == "m4a"))
                {
                    QUrl url = QUrl::fromLocalFile(song.path());
                    newPlaylist->addMedia(QMediaContent(url));
                    songFound=true;
                }
                song.next();
            }

            if(songFound) {
                int rowIndex = rowCount();
                beginInsertRows(QModelIndex(), rowIndex, rowIndex);
                mPlayListsList.push_back(move(newPlaylist));
                endInsertRows();
            }
        }
        it.next();
    }
}

QMediaPlaylist& PlayListModel::getPlaylistFromIndex(int index)
{
    return *mPlayListsList.at(static_cast<unsigned int>(index));
}

int PlayListModel::rowCount(const QModelIndex &parent) const
{
    (void)parent;
    return static_cast<int>(mPlayListsList.size());
}

QVariant PlayListModel::data(const QModelIndex &index, int role) const
{
    if (!isIndexValid(index)) {
        return QVariant();
    }

    const myPlaylist& album = *mPlayListsList.at(static_cast<unsigned int>(index.row()));

    switch (role) {     
        case PlaylistRoles::IconRole:
            return album.getPlaylistImage();

        case PlaylistRoles::IndexRole:
            return album.currentIndex();

        case PlaylistRoles::PlaybackRole:
            return album.playbackMode();

        case PlaylistRoles::SizeRole:
            return album.mediaCount();

        case PlaylistRoles::NameRole:
        case Qt::DisplayRole:
            return album.getPlaylistName(); //album.objectName();

        case PlaylistRoles::NextRole:
        case PlaylistRoles::PreviousRole:
            return QVariant();

        default:
            return QVariant();
    }
}

bool PlayListModel::setData(const QModelIndex &index, const QVariant &value, int role)
{
    if (!isIndexValid(index)
            || role != PlaylistRoles::PlaybackRole
            || role != PlaylistRoles::NextRole
            || role != PlaylistRoles::PreviousRole
            || role != PlaylistRoles::NameRole
            || role != PlaylistRoles::IconRole
            || role != PlaylistRoles::IndexRole) {
        return false;
    }

    myPlaylist& album = *mPlayListsList.at(static_cast<unsigned int>(index.row()));

    switch(role)
    {
        case PlaylistRoles::NameRole:
            album.setPlaylistName(value.toString());
            break;

        case PlaylistRoles::IconRole:
            album.setPlaylistImage(value.value<QImage>());
            break;

        case PlaylistRoles::PlaybackRole:
            //CurrentItemOnce, CurrentItemInLoop, Sequential, Loop, Random
            album.setPlaybackMode(static_cast<QMediaPlaylist::PlaybackMode>(value.toInt()));
            break;

        case PlaylistRoles::NextRole:
            album.next();
            break;

        case PlaylistRoles::PreviousRole:
            album.previous();
            break;

        case PlaylistRoles::IndexRole:
            album.setCurrentIndex(value.toInt());
            break;

        default:
            break;
    }

    emit dataChanged(index, index);
    return true;
}

QHash<int, QByteArray> PlayListModel::roleNames() const
{
    QHash<int, QByteArray> roles;
    roles[PlaylistRoles::IconRole] = "icon";
    roles[PlaylistRoles::PlaybackRole] = "playback";
    roles[PlaylistRoles::SizeRole] = "size";
    roles[PlaylistRoles::IndexRole] = "currentIndex";
    roles[PlaylistRoles::NameRole] = "name";
    return roles;
}

bool PlayListModel::isIndexValid(const QModelIndex &index) const
{
    if (index.row() < 0
            || index.row() >= rowCount()
            || !index.isValid()) {
        return false;
    }
    return true;
}

MusicPage.qml

import QtQuick 2.6
import QtQuick.Controls 2.0
import QtMultimedia 5.9
import "."

import "../menu"

PageTheme {
    property string playlistName
    property int playlistIndex

    toolbarTitle: playlistName + " " + playlistIndex

    MediaPlayer
    {
        id: playMusic
        autoLoad: true
        autoPlay: true
        playlist: {playlistModel.getPlaylistFromIndex(playlistIndex)}
    }

    MusicController
    {
        songPlayer: {playlistModel.getPlaylistFromIndex(playlistIndex)}
    }
}

For information the myPlaylist class is:

#ifndef MYPLAYLIST_H
#define MYPLAYLIST_H

#include <QtMultimedia/QMediaPlaylist>
#include <QImage>

class myPlaylist : public QMediaPlaylist
{
    Q_OBJECT
public:

    explicit myPlaylist(QObject* parent = nullptr);

    void setPlaylistName(QString name);
    QString getPlaylistName() const;

    void setPlaylistImage(QImage image);
    QImage getPlaylistImage() const;

private:
    QString mName;
    QImage mImage;
};

#endif // MYPLAYLIST_H

When I select the playlist in a pathView, the MusicPage QML page opens and I get the error Unable to assign [undefined] to ::QDeclarativeAudio*) for the line: playlist: {playlistModel.getPlaylistFromIndex(playlistIndex)}

What I'm doing wrong? Any suggestions for the whole structure are welcome.

Thank you in advanced.

Regards,
Davidino

sierdzio

@davidino said in Pass a Playlist from C++ to QML (error Unable to assign [undefined] to ::QDeclarativeAudio*):

Q_INVOKABLE QMediaPlaylist& getPlaylistFromIndex(int index);

You should return a pointer. And in case of unique_ptr, use .get().

davidino

Heelo @sierdzio ,

thank you for your reply. I've changed the code as :

QMediaPlaylist* PlayListModel::getPlaylistFromIndex(int index)
{
    return mPlayListsList.at(static_cast<unsigned int>(index)).get();
}

But I get the error Unknown method return type: QMediaPlaylist*
Any advices?

For information, I pass the Playlist model object as follow:

    PlayListModel playlistModel("/home/root");

    QQmlApplicationEngine engine;
    QQmlContext* context = engine.rootContext();
    context->setContextProperty("playlistModel", &playlistModel);

Thank you.

Regards.
Davidino

sierdzio

@davidino said in Pass a Playlist from C++ to QML (error Unable to assign [undefined] to ::QDeclarativeAudio*):

But I get the error Unknown method return type: QMediaPlaylist*

This should work: Q_DECLARE_METATYPE(QMediaPlaylist*).

davidino

@sierdzio said in Pass a Playlist from C++ to QML (error Unable to assign [undefined] to ::QDeclarativeAudio*):

Q_DECLARE_METATYPE(QMediaPlaylist*)

Hello @sierdzio ,
thank you for your message. I tried to add Q_DECLARE_METATYPE as per you indication in playlistModel.h:

Q_DECLARE_METATYPE(QMediaPlaylist*)

class PLAYLISTMODEL_EXPORT PlayListModel : public QAbstractListModel
{
    Q_OBJECT
public:

But I still get the error for the line playlistModel.getPlaylistFromIndex(playlistIndex)
Thank you for your assistance.

Regards,
Davidino

KroMignon

@davidino said in Pass a Playlist from C++ to QML (error Unable to assign [undefined] to ::QDeclarativeAudio*):

But I still get the error for the line playlistModel.getPlaylistFromIndex(playlistIndex)

The problem is that you property is set once/statically and there is no update, you should do something like this:

PageTheme {
    property string playlistName
    property int playlistIndex

    toolbarTitle: playlistName + " " + playlistIndex
    onPlaylistIndexChanged {
        var item = playlistModel.getPlaylistFromIndex(playlistIndex)
        //note: using double ! to check item is not null or undefined (little JavaScript trick)
        if(!!item) {
            playMusic.playlist = item;
            musicCtrl.songPlayer = item;
        }
    }

    MediaPlayer {
        id: playMusic
        autoLoad: true
        autoPlay: true
    }

    MusicController {
        id: musicCtrl
    }
}

davidino

Hello @KroMignon ,
thank you for your answer. Using this method for retrieving the playlist:
QMediaPlaylist& PlayListModel::getPlaylistFromIndex(int index)
{
return *mPlayListsList.at(static_cast<unsigned int>(index));
}
I don't get any error as before, but the check (if item is null) always return null.
As you can see below I modified the code so that the code show the number of songs in the selected playlist and there are songs! I don't get what it could be..

import "QUItMeterComponent"

import "../menu"

PageTheme {
    property string playlistName
    property int playlistIndex
    property int playlistSize

    id: musicPage
    toolbarTitle: playlistName + ": " + playlistSize + " songs"

    function changePlaylist() {
        var item = playlistModel.getPlaylistFromIndex(playlistIndex)
        //note: using double ! to check item is not null or undefined (little JavaScript trick)
        if(!!item) {
            playMusic.playlist = item;
            console.log("playlist changed!!");
        }
        else
            console.log("playlist no good!!");
    }

    onPlaylistIndexChanged: changePlaylist()

    MediaPlayer {
        id: playMusic
        autoLoad: true
        autoPlay: true
        //Component.onCompleted: changePlaylist()
    }

For information, if I tried the function getPlaylistFromIndex returning the pointer as written above, I still get the error Unknown method return type: QMediaPlaylist*.

Thank you for your assistance.

Regards,
Davidino

KroMignon

@davidino said in Pass a Playlist from C++ to QML (error Unable to assign [undefined] to ::QDeclarativeAudio*):

QMediaPlaylist& PlayListModel::getPlaylistFromIndex(int index)

As @sierdzio already written, to interface with QML you better return a pointer and not a reference. Please respect QML/C++ best practice, this will avoid you many problems!

have you taken time to read documentation? ==> https://doc.qt.io/qt-5/qtqml-cppintegration-overview.html

davidino

Hello @KroMignon ,
thank you for your posts I read several links inside it, however I have to say that since there are many possibilities, it gets complicated as well. I search on the net as well. Here some considerations:
First, I tried, instead of returning QMediaPlayer*, to return QObject* and QVariant, as explained, but in both cases I got runtime errors.

It sounds strange that I have to register it with Q_DECLARE_METATYPE(QMediaPlaylist*) considering that it's a QT Object. Could it be a bug as happened here with QAbstractListItem?
https://bugreports.qt.io/browse/QTBUG-68411

Despite of all, I'm still getting error Unknown method return type: QMediaPlaylist*..
I'm thinking to alternative approaches like passing QStringlist of Qurl, which is supported by QML, instead of QMediaplayist.

Best Regards,
Davide Brunelli