[Interest] QML ListView is not updated on model reset

[Alexander Dyagilev]

I have another ListView wich uses C++ model derived from another class - 
QSqlQueryModel.

The same things happens: model is not updated and existing items gets 
damaged. E.g. model.id for an item was 2 and became 0 after a new item 
has been added (all existing item's model.id becomes 0).

Something very wrong is happening. Look like I misunderstand something...


On 2/27/2017 8:59 PM, Alexander Dyagilev wrote:
>
> Hello,
>
> I've created a question on SO but nobody answered still...
> (http://stackoverflow.com/questions/42468811/qml-listview-is-not-updated-on-model-reset)
>
> Qt 5.8, Windows 10.
>
> Quick Controls 2 application. In QML I have a ListView with a model 
> derived from QAbstractListModel.
>
> In the model I have the following code:
>
> |voidMediaPlaylistModel::update(){beginResetModel();{std::unique_lock<std::mutex>lock(m_mutex);m_ids 
> =m_playlist->itemsIds();}endResetModel();}|
>
> Nothing happens in QML view after calling this method: list is not 
> updated. If I go back and then forward (to the page with the ListView) 
> - it'll contain updated data. Model object instance is the same always.
>
> Am I doing something wrong?
>
> *Update #2*:
>
> C++ model code:
>
> |MediaPlaylistModel::MediaPlaylistModel(QSharedPointer<AbstractMediaPlaylist>playlist,QObject*parent):base_t(parent),m_playlist(playlist){Q_ASSERT(m_playlist);connect(playlist.data(),&AbstractMediaPlaylist::changed,this,&MediaPlaylistModel::update);update();}QHash<int,QByteArray>MediaPlaylistModel::roleNames()const{QHash<int,QByteArray>result;result[IdRole]="id";result[TitleRole]="title";result[DurationRole]="duration";returnresult;}voidMediaPlaylistModel::update(){Q_ASSERT_SAME_THREAD;beginResetModel();{std::unique_lock<std::mutex>lock(m_mutex);m_ids 
> =m_playlist->itemsIds();}endResetModel();}intMediaPlaylistModel::rowCount(constQModelIndex&parent)const{Q_UNUSED(parent);std::unique_lock<std::mutex>lock(m_mutex);returnstatic_cast<int>(m_ids.size());}QVariantMediaPlaylistModel::data(constQModelIndex&index,introle)const{autorow 
> =static_cast<size_t>(index.row());intid 
> =0;{std::unique_lock<std::mutex>lock(m_mutex);if(row 
> >=m_ids.size())returnQVariant();id =m_ids[row];}if(role 
> ==IdRole)returnid;QVariantresult;autoitem 
> =m_playlist->item(id);switch(role){caseQt::DisplayRole:caseTitleRole:result 
> =item.title;break;caseDurationRole:result 
> =item.duration;break;}returnresult;}|
>
> QML code:
>
> |importQtQuick2.7importQtQuick.Controls2.0importcom.company.application 
> 1.0Page{id :root propertyintplaylistId propertyvar 
> playlistApi:App.playlists.playlist(playlistId)ListView{id :playlist 
> anchors.fill:parent model:playlistApi.model 
> delegate:ItemDelegate{text:model.title width:parent.width 
> onClicked:App.player.play(playlistId,model.id)}ScrollIndicator.vertical:ScrollIndicator{}}}|
>
> *Update #3*:
>
> When the model is updated (one item added), something strange happens 
> with QML ListView: in addition to fact that it's not updated (and it 
> does not call MediaPlaylistModel::data to retrieve new items), 
> *existing items got damaged*. When I click on existed item, it's 
> model.id property is always 0. E.g. at app start its model.id was 24, 
> after one item added its model.id became 0.
>
> *Update #4*:
>
> App.playlists.playlist(playlistId) returns pointer to this class instance:
>
> |classCppQmlPlaylistApi:publicQObject{Q_OBJECT Q_PROPERTY(QObject*model 
> READ model NOTIFY modelChanged)Q_PROPERTY(QStringtitle READ title 
> WRITE setTitle NOTIFY 
> titleChanged)public:explicitCppQmlPlaylistApi(intplaylistId,QWeakPointer<CorePlaylistsManager>playlistsMgr,QObject*parent 
> =0);QObject*model()const;QStringtitle()const;voidsetTitle(constQString&title);signals:voidmodelChanged();voidtitleChanged();voidloadPlaylistRequested(intid);protectedslots:voidonPlaylistLoaded(intid);voidonPlaylistRemoved(intid);protected:intm_playlistId 
> =0;QWeakPointer<CorePlaylistsManager>m_playlistsMgr;QSharedPointer<QAbstractItemModel>m_model;};|

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