Important: Please read the Qt Code of Conduct -

[Solved]Parameter Qt::ItemDataRoles doesn't matchs with the expected values.

  • Hi guys.

    I'm working in a application where I make a custom model from QAbstractItemModel, in this I have a container of a custom class, and I like to show that data in a QTableView. But in the beginning the view dont show the values of the items, so I'm looking over the overrided data function.

    @#include "playlistmodel.h"





    int PlayListModel::rowCount(const QModelIndex &parent) const{
    return m_lstAudioMetaObj.size();

    int PlayListModel::columnCount(const QModelIndex &parent) const{
    return 7;

    QVariant PlayListModel::data(const QModelIndex &index, int role) const{
    return QVariant();
    return QVariant();
    if(role!=Qt::DisplayRole){ //!
    if(index.column()== 0){
    QVariant v(m_lstAudioMetaObj[index.row()].artist());
    return v;
    return QVariant();

    bool PlayListModel::insertData(const AudioMetaData &audio){

    int tempSize=m_lstAudioMetaObj.size();
    if(m_lstAudioMetaObj.size() >tempSize)
        return true;
    return false;


    QVariant PlayListModel::headerData(int section, Qt::Orientation orientation, int role) const{
    if(orientation != Qt::Horizontal || role != Qt::DisplayRole)
    return QAbstractItemModel::headerData(section,orientation,role);

    case 0: return "Name";
    case 1: return "Release Time";
    case 2: return "Artist";
    case 3: return "Album";
    case 4: return "Genre";
    case 5: return "Rating";
    case 6: return "Duration";
    return QVariant();


    In the line 27 I'm trying to show the data of the respectly AudioMetaData, but the view isn't works and shows:


    Then, I looked more deeply and found that the expected roles values wasn't matchs with the expected values (Qt::DisplayRole), throwing the following values:

                 Name    Release         Artist                  Album             Genre             Duration     Rating

    (Role Value) 6 7 9 10 1 8 ?

    Notice that the last column(rating) is ignore and continue with the next row (tested)...So the questions are...

    1.-How or Where can I set the values of each AudioMetaValue?

    2.- And if that isn't possible. What do you suggest to fix it?

    Thank You.

    Your trusly, Carlos Hernandez. Wiwiped.

    PS. If you need them, I give you the definitions and implementations of the others classes.

    @#ifndef PLAYLISTMODEL_H

    #include <QAbstractTableModel>
    #include <QModelIndex>
    #include <QList>
    #include <QVariant>
    #include "audiometadata.h"

    class PlayListModel : public QAbstractTableModel
    PlayListModel(QList<AudioMetaData> lst, QObject* parent=0):
    //Implemented Function
    int rowCount(const QModelIndex &parent= QModelIndex()) const;
    int columnCount(const QModelIndex &parent=QModelIndex()) const;
    QVariant data(const QModelIndex &index, int role=Qt::DisplayRole) const;
    bool insertData(const AudioMetaData& audio);
    QVariant headerData(int section, Qt::Orientation orientation, int role) const;

    QList&lt;AudioMetaData&gt; list()const{return m_lstAudioMetaObj;}


    #endif // PLAYLISTMODEL_H

    @#include "audiometadata.h"



    AudioMetaData::AudioMetaData(const AudioMetaData &other){

    @#ifndef AUDIOMETADATA_H

    #include <QObject>
    #include <QString>
    #include <QDate>
    #include <QTime>

    class AudioMetaData
    explicit AudioMetaData(QString n,QDate d,QString a,QString al,
    QString g,QTime du,int r):m_name(n),m_dateOfRelease(d),

    AudioMetaData(const AudioMetaData& other);
    //Access Function.
    QString name()const{return m_name;}
    void setName(QString name){m_name=name;}
    QDate dateOfRelease()const{return m_dateOfRelease;}
    void setDate(QDate date){m_dateOfRelease=date;}
    QString artist()const{return m_artist;}
    void setArtist(QString artist){m_artist=artist;}
    QString album()const{return m_album;}
    void setAlbum(QString album){m_album=album;}
    QString genre()const{return m_genre;}
    void setGenre(QString genre){m_genre=genre;}
    QTime duration()const{return m_duration;}
    void setDuration(QTime duration){m_duration=duration;}

    QString m_name;
    QDate m_dateOfRelease;
    QString m_artist;
    QString m_album;
    QString m_genre;
    QTime m_duration;
    int m_Rating;

    #endif // AUDIOMETADATA_H

  • And If you have some suggestion about my code style, It will be appreciated : )

  • Moderators

    you just don return anything for Qt::DisplayRole in your data() method.
    So why should the view display anything? :)

    Maybe it's a typo but shouldn't it be look like this?!
    if(role == Qt::DisplayRole){
    if(index.column()== 0){
    QVariant v(m_lstAudioMetaObj[index.row()].artist());
    return v;

  • Thank you raven.

    Well, that part of code is so because I was testing

    I'm expeting values of Qt::DisplayRole role, but instead that I saw that values vary as this:

    For name column, role value is 6
    For release column, role value is 7
    Duration column, role value is 8
    and for rating column, role value is invalidated.

    So, the questions are:

    Why role values vary as that form when I'm expecting only Qt::DisplayRole because AudioMetaData members are all QString unless Rating (int) ?

    How can I ensure Qt::DisplayRole role with my AudioMetaData?

  • bq. Maybe it’s a typo but shouldn’t it be look like this?!

    Yes Indeed, But I saw that that if isn't work so I changed the setence.

  • Moderators

    [quote author="Charlie_Hdz" date="1422380725"]Why role values vary as that form when I'm expecting only Qt::DisplayRole because AudioMetaData members are all QString unless Rating (int) ?[/quote]The View will always ask for data from many different roles. This is expected.

    For example:

    • It asks for Qt::DisplayRole (0) to get the text
    • It asks for Qt::BackgroundRole (8) to get the cell colour
    • It asks for Qt::ForegroundRole (9) to get the text colour

  • Lifetime Qt Champion


    DisplayRole is only one part of what's needed to show something in a view. The other roles comprises font, text color, background color etc. That's why when you don't hand a particular role you return the value of the base class implementation.

  • I understand now.

    I read some documentation as "Model/View Tutorial": and "Model/View Programming": again

    So I only make some changes and everything work excellent.

    @QVariant PlayListModel::data(const QModelIndex &index, int role) const{
    return QVariant();
    return QVariant();
    if(role == Qt::DisplayRole){
    int column=index.column(); int row=index.row();

       case 0:            return QString("%1").arg(;
       case 1:           return QString("%1").arg(
       case 2:           return QString("%1").arg(;
       case 3:           return QString("%1").arg(;
       case 4:           return QString("%1").arg(;
       case 5:           return QString("%1").arg(;
       case 6:           return QString("%1").arg(;

    return QVariant();


    So I'll continue with my projects...

    Thank you everyone.

Log in to reply