CODEWITHSUNDEEP
c++qt
Klaim
Klaim

Reputation: 69752

What are the possible reasons for an `emit dataChanged( ... );` to not trigger view's display update?

I'm implementing my 3rd "naive" model as QAbstractItemModel inheriting class.

So far it worked well. However, I've been using read-only "static" models in my views and only changed the model of some views depending on the user's actions. So I used my_view->setModel( a_model ); to update a view.

Now I need to have one of the views to keep a unique model but that model needs to be update sometimes, using a special function "update()" function that I call in the code when required.

At the end of the update() function, I just call emit dataChanged( ... ); with the corresponding data.

It seems that it doesn't update the view this model is connected to. The only way to make the view update seems to do something like my_view->setModel( nullptr ); then my_view->setModel( a_model ); again.

What are the possible reasons for an emit dataChanged( ... ); to not trigger view's display update?

I've been debugging my model implementation functions and the index() function get called but not the data(). I'm a bit worried that maybe I didn't understood something about the model/view system in the case of changing model (that is not changed through the view but programmatically).

It's an open-source project so you chan check the full model code there (it's a bit hacky I think, not used to model/view system of Qt) : http://code.google.com/p/art-of-sequence/source/browse/tools/aosdesigner/view/model/LayerObjectsModel.cpp?spec=svn4fe209aa3e82f2c7cd42192581a890e28bada9b0&r=4fe209aa3e82f2c7cd42192581a890e28bada9b0 The code of the widget managing the view is available there : http://code.google.com/p/art-of-sequence/source/browse/tools/aosdesigner/view/LayersView.cpp?spec=svn4fe209aa3e82f2c7cd42192581a890e28bada9b0&r=4fe209aa3e82f2c7cd42192581a890e28bada9b0

Upvotes: 1

Views: 1980

Answers (1)

pnezis
pnezis

Reputation: 12331

I checked a bit Qt documentation. dataChanged() should be emitted when existing data of the model changes.

If you are adding rows to the model check beginInsertRows and endInsertRows

From the insertRows Qt documentation:

If you implement your own model, you can reimplement this function if you want to support insertions. Alternatively, you can provide your own API for altering the data. In either case, you will need to call beginInsertRows() and endInsertRows() to notify other components that the model has changed.

If you are removing rows from the model check correspondingly beginRemoveRows and endRemoveRows

Also have a look at beginResetData

When a model radically changes its data it can sometimes be easier to just call this function rather than emit dataChanged() to inform other components when the underlying data source, or its structure, has changed.

Upvotes: 4

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