C++ custom treemodel viewing in QML

[Dragann]

hello folks,

I have subclassed a QAbstractItemModel to create a custom tree model.

i would like to be able to show specific data in a QML view according to the parent-child structure.

for example, the tree holds Groups as top-level items and folders as children. The folders also have children items corresponding to files and the files also have children. So what i would want to see is something like:

---

Groupname1
folder1
info1, info2, info3

folder2
info1, info2, info3

folder3
info1, info2, info3

---

Groupname2
folder1
info1, info2, info3

folder2
info1, info2, info3

folder3
info1, info2, info3

and so on.

the info1-2-3 could be specific data about the folders such as filecount, or ownername.

i have seen lots of examples that only show simple c++ listmodels but nothing like this.

It would be possible to hack around it but i am looking for the proper way to do something like this, so if somebody could point me in the right direction, that would be really phucking awesome!

[sierdzio]

QML currently supports only lists. There is no tree support. It will be added in Qt 5.5.

[Dragann]

yes i am aware of that, nonetheless people have still managed to pull it off using nested views. So i am looking for a way to do it using just listviews.

I am sure it must be possible in some way to display specific data from a treemodel using nested views

[sierdzio]

You can use model roles to display the nesting inside concrete items, for example. So, pass a "column" role from the model and in the item add indentation based on that value. You can also leverage ListView's sections.

[Dragann]

would it be possible to post an example? I just picked up model/view programming from the "Advanced QT Programming" book.. so the c++ model part i understand, but the QML part is very new to me.

[sierdzio]

@
// Assuming the model has "column" role, "modelText" role and "group" role

ListView {
delegate: Rectangle {
// inside the delegate, you can use named roles from the model
Row {
Text { id: t1; text: (column == 0)? modelText : "" }
Text { id: t2; text: (column == 1)? modelText : "" }
Text { id: t3; text: (column == 2)? modelText : "" }
}
}

// Optional: sections
section.property: group
section.delegate: Text { text: group }
}
@

Of course, this is just a quick draft, it can be improved a lot.

[Dragann]

these roles are confusing me... would this mean that every data item in the tree has these attributes? that would mean that every item would hold data about the group and the column... would this not be redundant?

it would mean that every item, including file items and everything else would hold data about the group it is in.

correct me if i am wrong.

my tree structure looks like this

@Group1
Folder1
File1
File2
size
format
extension
etc
File3
size
...
...
Folder2
...
Group2
...
...
...
...
...
...
...
...
...
@

if i have understood correctly, roles are attributes of items. Meaning that every item should have those attributes, meaning that even group items would have group role attributes... even format and size items would contain information about the group they are in. It all seems redundant and just doesnt make sense.

Maybe i just understand it all wrong but this setup does not have columns.. this data is all just variables that come from different tables from a relational sql database..

---

Group1
folder1
folder2
folder3

Group2
folder1
folder2
....

and when you click on a folder,, it should show a new screen like

Folder1
file1
file2
file3

Folder2
file1
file2

so if i want to display the above data like this, is your example still valid?

and thank you very much for taking the time to help me, i really really apreciate it very much.

[sierdzio]

[quote]Maybe i just understand it all wrong but this setup does not have columns[/quote]

Correct. As mentioned above, QML currently does not support columns. So in my draft I attempted to fake column support by using roles. I agree it is not a perfect solution. Other I've seen often include creating separate ListViews for all subitems. This is not nice either.

I've added "section" properties because you seem to have use for it. I have not used that functionality myself, so perhaps my draft code would not work.

[quote]so if i want to display the above data like this, is your example still valid?[/quote]

In that case I think you could use standard ListView, standard 1D list, create separate ListView for each "level" of detail. You can switch between those levels using a Loader, or state transitions, or some other way.

[Dragann]

bq. n that case I think you could use standard ListView, standard 1D list, create separate ListView for each “level” of detail

this is also what i was thinking. But the question is: for example, How would i make a listview that show only the top level items of my treemodel so that only the children of the rootitem are shown (the groups).. if i know this i can make different lists that show specific details of certain items just like you said. I would be able to select a folder and make a list that shows all the children of the folder (all the files).

oh and thank you again, i cannot say how much i apreciate the help because i always try to figure stuff out completely on my own