CODEWITHSUNDEEP
pythonqtpyqtpyside
Mathieson
Mathieson

Reputation: 1292

How to keep multiple QAbstractItemModel classes in sync

I've been working really hard trying to find a solution to this for the past few weeks. I have committed to a direction now, but I am still not entirely satisfied with what I have come up with. Asking this now purely out of curiosity and for hope of a more proper solution for next time.

How on earth do I keep multiple QAbstractItemModel classes in sync that are referring to the same source data but displaying in different ways in the tree view?

One of the main reasons for using model/view is to keep multiple views in sync with one another. However, if each of my views requires different data being displayed at the same column, as far as I can tell I need to then subclass my model to two different models with different implementations that will then cater to each of those unique view displays of the same items.

Underlying source items are the same, but data displayed is different. Maybe the flags are different as well, so that the user can only select top level items in one view and then can only select child items in the other view.

I'll try to give an example:

Lets say my TreeItem has three properties: a, b, c.

I have two tree views: TreeView1, TreeView2. Each has two columns.

TreeView1 displays data as follows: column1 -> a, column2 -> b

TreeView2 displays data as follows: column1 -> a, column2 -> c

I then need to create two different models, one for TreeView1 and one for TreeView2, and override the data and flags methods appropriately for each.

Since they are now different models, even though they are both referring to the same TreeItem in the background, they are no longer staying in sync. I have to manually call the refresh on TreeView2 whenever I change data on TreeView1, and vice versa.

Consider that column1, or property a, is editable and allows the user to set the name of the TreeItem. Desired behaviour would be for the edit that is done in TreeView1 to instantly be reflected in TreeView2.

I feel like I am missing some important design pattern or something when approaching this. Can anyone out there see where I am going wrong and correct me? Or is this a correct interpretation?

Thanks!

Upvotes: 2

Views: 627

Answers (1)

Kuba hasn't forgotten Monica
Kuba hasn't forgotten Monica

Reputation: 98495

One way to do it is to use viewmodels. Have one QAbstractItemModel adapter to your underlying data model. All interaction must pass through that model. When you need to further adapt the data to a view, simply use a proxy view model class that refers to the adapter above and reformats/adapts the data for a view. All the view models will then be automagically synchronized. They can derive from QAbstractProxyModel, although that's not strictly necessary.

There is no other way of doing it if the underlying source of data doesn't provide change notification both for the contents and for the structure. If the underlying data source provides relevant notifications, it might as well be a QAbstractItemModel to begin with :)

Upvotes: 2

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