[Qt-interest] QAbstractItemModel, tree structure and dynamic datas

[Girish Ramakrishnan]

Tanguy Krotoff wrote:
> Hello
> 
> I can easily make my QAbstractItemModel be updated with new datas
> dynamically when QAbstractItemModel is a simple list.
> 
> But I have some hard time to get this done with a tree structure like this one:
> + item1
>     - item11
>     - item12
> (screenshot: http://www.ldc.usb.ve/docs/qt/images/windowsxp-treeview.png )
> 
> Here what I would like to achieve:
> The user clicks on the "+" in front of item1:
>   - In another thread is done some computation
>   - When the computation is done, a signal computationDone(result) is sent
>   - The child items of item1 are getting added
> 
> To sum up, I would like to populate an item with its childs
> dynamically using a different thread. Why? I want a responsive GUI and
> the internal tree structure can be very big
> 
> 
> Here what I have understood from the documentation, examples and mails
> from this mailing-list:
> - The "+" in front of item1 is showed when hasChildren() returns true
> - When the user clicks on the "+", method canFetchMore() is being
> called. If true is returned, it will call method fetchMore()
> 
> Here what I would like to implement inside my
> QAbstractItemModel::fetchMore() method:
> 
> fetchMore(const QModelIndex & parent) {
> 	computeInAnotherThread(parent);
> 	//emits signal computationDone()
> }
> 
> //Catches signal compuationDone()
> slotComputationDoneFromOtherThread(const QStringList & childs) {
> 	beginInsertRows(parent, first, last);
> 	foreach (QString child, childs) {
> 		//Change my internal tree data structure
> 	}
> 	endInsertRows();
> }
> 

Look correct to me. What is the problem you are facing?

> Is it the right way to do it? Am I wrong about the use of
> canFetchMore() and fetchMore()? Is there some examples/projects around
> using QAbstractItemModel this way?
> 

4.5 has an example http://doc.trolltech.com/4.5/itemviews-fetchmore.html

Girish