Introduce a new example using a QSortFilterProxyModel

[Ahuge]

This implements a custom QAbstractItemModel and QSortFilterProxyModel

[mappu]

Nice, thank you for the PR! It compiled fine for me and sorting the Size column does correctly understand the byte value of the files.

[mappu]

When starting up the example, I got these terminal messages:

Error converting %!s(int=0) to int: strconv.Atoi: parsing "": invalid syntax
Error converting %!s(int=0) to int: strconv.Atoi: parsing "": invalid syntax
Error converting %!s(int=0) to int: strconv.Atoi: parsing "": invalid syntax
Error converting %!s(int=0) to int: strconv.Atoi: parsing "": invalid syntax
Error converting %!s(int=0) to int: strconv.Atoi: parsing "": invalid syntax
Error converting %!s(int=0) to int: strconv.Atoi: parsing "": invalid syntax

They repeat when attempting to sort by the Name column,

[Ahuge]

Ah thanks I will fix that!

[mappu]

There are some extra rules when passing pointers between Go and C. One of the rules is: If there is no Go pointer to the TreeItem, only a C++ pointer, then Go might GC the variable, and this could become a use-after-free.

Is there any other place this TreeItem is reachable other than from Qt (C++) memory? If not, a workaround is to either (A) ensure that the TreeItems are stored in some long-lived application struct or global variable; or (B) call runtime.Keepalive() at some later point.

[mappu]

Or (C) Wrap the thing in a cgo.Handle before putting it in Qt space, and unwrap it when pulling it out again. This is what Miqt mostly does internally.

[Ahuge]

Ok so the TreeItem is created in PopulateData and the rootItem keeps track of its children.
And we keep a reference to the rootItem.

I don't know if that is enough to keep it alive.

I am not super clear if pulling in a a pointer from the QModelIndex and then casting it to a TreeItem pointer is the right way to do that, I am open to another way to get the modelItem from a QModelIndex if there is one.

item = (*TreeItem)(parent.InternalPointer())
If I call runtime.KeepAlive(item) everytime that I get the InternalPointer, will that cause a memory leak?
Isn't QModelIndex.internalPointer() a go pointer anyways?

[mappu]

The sort size is stored in a QVariant as a string. Then later, we parse it. It might be simpler to use the QVariant constructor that stores an int directly,

[Ahuge]

Good call

[mappu]

In the default view, the Size column is initially truncated, so I went to resize the window larger. But something about the QSizePolicy is meaning the treeview will not grow when the window is resized (although it does shrink). I think this could be fixed in a 1 line change, but I haven't checked exactly.

[Ahuge]

So I took a deeper look at this.

I can't figure out how to make this work as I would expect.

The only way I can get it working is with the following hack:

dialog.OnResizeEvent(func(super func(event *qt.QResizeEvent), event *qt.QResizeEvent) {
		dialog.ResizeWithQSize(event.Size())
                // Width minus dialog.ContentMargins Left/Right
		treeView.Resize(event.Size().Width()-20, treeView.Size().Height())
	})

But having written Qt before, obviously that is a messy hack.

Is there a possibility that the default Resize events aren't being propagated down to child widgets?