Dynamic Upadate of data to a ListModel

[raven-worx]

@saitej said in Dynamic Upadate of data to a ListModel:

How do I update the values when there is a change in the values?

you need to emit the dataChanged() signal from your model whenever the data for a given index changes.

[m.sue]

Hi,
...or use the begin*, end* functions described in doc.qt.io/qt-5/qabstractitemmodel.html#protected-functions and e.g. used in this example http://doc.qt.io/qt-5/model-view-programming.html. This will probably result in calling the dataChanged() signal indirectly :-)
-Michael.

[saitej]

Thanks!!

I will try and update if it works

[saitej]

@m.sue

I am not adding a new row. I am only modifying a value so I guess datachanged() is a better choice.

[raven-worx]

@m.sue said in Dynamic Upadate of data to a ListModel:

This will probably result in calling the dataChanged() signal indirectly :-)

actually no.
The dataChanged() signal is for the case (surprise) when the data (of an existing item) has changed .
The methods mentioned by you should be self-explanatory. So there is no dataChanged() signal necessary.

[m.sue]

@saitej: you had an addDatamethod, so I suspect you would really add some data.
@raven-worx: Ah, I see, then they probably emit the \*AboutToBe\* signals, as somehow, of course, the widget must know about these actions.
-Michael.

[saitej]

@m.sue

Ya for adddata method I am already using the beginInsertRows :)

[saitej]

@raven-worx

Hi

I didn't get you. If I need to change the existing data, how do i do it with out datachanged() signal

[raven-worx]

@m.sue said in Dynamic Upadate of data to a ListModel:

Ah, I see, then they probably emit the *AboutToBe* signals, as somehow, of course, the widget must know about these actions.

yes, the QAbstractItemView of course does connect to those signals. If you have a custom object/widget, you would also need to connect to those signals.

@saitej said in Dynamic Upadate of data to a ListModel:

I didn't get you. If I need to change the existing data, how do i do it with out datachanged() signal

i said: you only need in the case existing data has changed

[saitej]

@raven-worx

void QAbstractItemModel::dataChanged(const QModelIndex &topLeft, const QModelIndex &bottomRight, const QVector<int> &roles = QVector<int> ())

Is this used to update the entire model or Can it be used to update a specific item in the listview? If It can be used to update a specific item then what are the arguments (instead of bootrom right)?

Thanks!!

[raven-worx]

@saitej
if it's just a single cell, then topLeft and bottomRight are the same index.
If you want to update the whole row, then topLeft is QModelIndex(row,0) and bottomRight is QModelIndex(row,colCount-1).
Also it is possible to set topLeft to QModelIndex(0,0) and bottomRight to QModelIndex(rowCount-1,colCount-1) to update the whole table/list.

Note that ranges are only supported when topLeft and bottomRight have the same parent index. So as long as you don't use your model in a treeview your are fine.

[saitej]

@raven-worx

Thanks a lot!!

[saitej]

@raven-worx

Hi

I am trying to connect a property change signal to datachanged signal through the following code.

for(int i=0;i<model.rowCount();i++)
    {
         if(model.data(model.index(i),UAVDataModel::NameRole).toString() == "Initial Polygon Area" ){
             connect(&av1,SIGNAL(initialPolygonAreaChanged(qreal)),&model,SIGNAL(dataChanged(model.index(i),model.index(i))));
         }

    }

I am getting an error

QObject::connect: No such signal DataModel::dataChanged(model.index(i),model.index(i))

Note: I have not redeclared the signal in the model as it is inherited from QAbstractListModel

[raven-worx]

@saitej
thats not how signal/slot connections work.
Rather you should connect the model's dataChanged() signal to a slot of yours, and in the slot check the passed index if it's the row/column you want.

[saitej]

@raven-worx

I am not editing the data, it is only displaying data from a source. So connecting datachanged signal to a slot does not make sense.

we can use connect() to connect 2 signals right?

[raven-worx]

@saitej said in Dynamic Upadate of data to a ListModel:

So connecting datachanged signal to a slot does not make sense.

sorry but that doesn't make sense. I think you still don't understand the concept.
It doesn't matter if you edit the data or not.

The dataChanged() signal notifies the receiver (-> slot) that the data of the given index(es) has changed, and the data needs to be retrieved from the model again.

[saitej]

@raven-worx

I got what datachanged signal does. I would like to explain my problem better. Sorry for the inconvenience.

For ex:
I have a signal initialPolygonAreaChanged(qreal) emitted when ever initialPolygonArea is changed . I know the index of initialPolygonArea in the model. I need to connect the initialPolygonAreaChanged(qreal) with datachanged() signal. Is this the right way?

[raven-worx]

@saitej said in Dynamic Upadate of data to a ListModel:

Is this the right way?

so far so good. You can also emit the dataChanged() signal whenever you emit initialPolygonAreaChanged(), since you know the index. (If the initialPolygonAreaChanged() signal is defined in the model)

[saitej]

@raven-worx

It is not defined in the model so I was to trying to connect via this:

connect(&av1,SIGNAL(initialPolygonAreaChanged(qreal)),&model,SIGNAL(dataChanged(model.index(i),model.index(i))));

What should this be changed to?

[raven-worx]

@saitej said in Dynamic Upadate of data to a ListModel:

connect(&av1,SIGNAL(initialPolygonAreaChanged(qreal)),&model,SIGNAL(dataChanged(model.index(i),model.index(i))));

This is not a valid connect statement. You are not allowed/supposed to do do a connection with the values already specified.

You will have to do something like this:

connect(&av1,SIGNAL(initialPolygonAreaChanged(qreal)),&model,SIGNAL(onInitialPolygonAreaChanged(qreal));

In your model's onInitialPolygonAreaChanged(qreal) slot you then emit the dataChanged() signal with the correct indexes.