Introduce Interface for TreeData used by TreeDataProvider

[cdir]

Description

TreeDataProvider uses TreeData as its source of data. As far I can see TreeDataProvide only needs a free methods (read-only) of TreeData:

• getRootItems()
• getChildren(item)
• contains(item)

The implementation of TreeDataProvide seems to fulfill my requirements, but I don't want to load all children right at the beginning, but only when the children are needed.

[sclassen]

I come to the same issue from a different path.

We have in our project a data structure which is a tree that we fetch from the DB.
All business logic is implemented on the data structure and we want to use TreeData to display the tree.
Currently we have logic implemented which replicates the tree in TreeData and when we we use drag-drop to re-arrange items in the tree we need to apply the changes both to the TreeData and our data structure. This is tedious an error prone.

I would like to open a PR which adds an interface to TreeData that is then used in the TreeDataProvider instead of the explicit class TreeData.

Any input is greatly appreciated

[mshabarov]

@sclassen thanks for the insights and willing to contribute.
The idea of introducing an interface for TreeData makes sense to us, could you file a pull request ?
Open question is the naming (HierarchicalTreeData can be just HierarchicalData) and the methods surface of this new interface - should it have only read-only methods as author noted, should we have two interfaces (read and read+write methods) and what methods do we expect in this method interface, e.g. your change doesn't have clear() and remove(), but why not including them. We can discuss in the PR.