Changing of C++ model doesn't update QML ListView

FOXLISIN

Hi. During the process of moving from QWidgets to QML I faced with the next problem: changing of C++ model doesn't update QML ListView. But on QWidgets all works as expected, i.e: emitting of dataChanged(index(0), index(rowCount())) signal updates my QListView from QWidgets.

My C++ model gets data through "Dispatcher" class, which returns different count of elements and values for roles for different ID, for example:

rowCount(...) method of my model looks like this:

int ChatModel::rowCount( const QModelIndex &theIndex ) const
{
    return _ChatDispatcher->messageCount();
}

And here is messageCount() method of my Dispatcher: _DialogID - field of Dispatcher class

int ChatDispatcher::messageCount()
{
    return GetMessagesCount( _DialogID );
}

And when i change _DialogID i want to redraw the ListView by emitting dataChanged(index(0), index(rowCount())) signal. But for QML ListView it doesn't work.

I've tryed this instead of dataChanged(..):

beginResetModel();
endResetModel();

It works, but very slowly. Maybe you advise me something useful?

dynamo72

Maybe this helps: if the number of rows changes, you have to call also QAbstractModel::beginInsertRows() and endInsertRows() - these take care of emitting the signals like rowsAboutToBeInserted() etc. - and these seem to be important for QML view updates.

p3c0

@FOXLISIN Can you post the code where you call dataChanged ?

FOXLISIN

@p3c0

I call it by click on Qml button:

RoundedButton {
        id: sendButton;

        text: "send";

        anchors {
            right: parent.right;
            bottom: parent.bottom;
            rightMargin: dp(15);
            bottomMargin: dp(15);
        }

        onClicked: sendMessage();
    }

    function sendMessage()
    {
        if( messageInput.text !== "" ){
            chatDispatcher.addMessage( messageInput.text );
            messageInput.text = "";
            chatModel.updateMessageView();
        }
    }

And i've tryed to emit dataChanged() signal like that:

void ChatModel::updateMessageView()
{
    dataChanged( index( 0 ), index( rowCount() ) );
}

p3c0

@FOXLISIN I dont see where you add new data in the model. What does addMessage do ? The list will show new data only when new data is available in the model.

FOXLISIN

@p3c0
My model gets all data from database through my "Dispatcher" class as i described above.

See:

int ChatModel::rowCount( const QModelIndex &theIndex ) const
{
    return _ChatDispatcher->messageCount();
}

And addMessage method inserts data to database. After that i want to redraw my listview

p3c0

@FOXLISIN Did you try checking rowCount() after you added new message ? Does it get updated ?

ahmad98

@FOXLISIN said in Changing of C++ model doesn't update QML ListView:
did you solve this problem ?

IntruderExcluder

The dataChanged signal of models in QML should also say which roles are changed. The 3rd param is missing.

GrecKo

When no roles are passed as a parameter, all roles ares assumed to be changed.

The most likely error of OP is to not call begin/endInsertRows (or modelReset is all the model is changed)