Qt View/Model/Data Paradigm: How to modify data?

Question

I just read the Model/View documentation for Qt 4.8. I believe to understand how the Model/View (Delegates/SelectionModel) work. One thing that I'm unsure about is how to manipulate data when I have a for example a TreeView.

Imagine having a TreeView to display a list and buttons to remove elements from this list when an item/row is selected. I see two approaches here

1) In the slot of the PushButton I retrieve the SelectionModel and the ItemModel of the TreeView and call model->removeRow(index.row ...). This way the model (that i subclassed from QAbstractItemModel) manipulates the data that it is supposed to represent.

2) In the slot of the PushButton I remove the item directly from the data source, that the TreeView's model represents. Then I can link the data with the model via signals/slot, such that the model can then tell the TreeView that the underlying data has changed.

The same scenario can be imagined with adding elements. Should I add the new element to the data which signals its changed state to the ItemModel which the informs the TreeView, or should I add the new item through the ItemMode?

I haven't found any Best Practices documentation on this. The two approaches differ strongly, such I would like to know in advanced which one is preferable.

Does anybody have a suggestion which path to follow?

Thanks

Jimmy Jimmy · Accepted Answer · 2012-07-09T10:31:24

1) is preferable - you should probably avoid manipulating your data source directly from the UI code - your life will be better if you go through the model. At the very least add a method to your model to do the data manipulation, and call that method from your UI code.

You will find that some of Qt's methods are protected such that they can only be called from the model itself (e.g. endInsertRows etc.)

Qt View/Model/Data Paradigm: How to modify data?

1 Answers