[Kde-bindings] Qyoto memory problem

[Jordan Miner]

Hi Dimitar,

Thanks for looking at it. I tried using `new QTreeWidgetItem(root)`,
but it did not make a difference.

It might be a hard problem to solve, but ideally, Qt would act like a
.NET library. In a .NET library, you don't have to think about whether
an object has ownership of another, because as long as there is a
reference to the object, it won't get collected. All other .NET
libraries that I've used, including System.Windows.Forms, are fully
garbage collected (and you cannot write code with them where a
GC.Collect() can change behavior). In the code below, ideally, the
signal-slot connection would keep the wrapper object alive. Is this
difficult to implement?

class Test2 : QMainWindow
{
    class Wrapper : QObject
    {
        Action dg;
        public Wrapper(Action dg)
        {
            this.dg = dg;
        }
        [Q_SLOT]
        public void Invoke()
        {
            dg();
        }
    }

    public Test2()
    {
        QPushButton button = new QPushButton("Push Me!");

        var wrapper = new Wrapper(delegate
        {
            QMessageBox.Information(this, "Clicked", "You clicked the
button.", QMessageBox.StandardButton.Ok);
        });
        Connect(button, SIGNAL("clicked()"), wrapper, SLOT("Invoke()"));
        wrapper = null;
        GC.Collect();

        CentralWidget = button;
        Show();
    }

    [STAThread]
    public static int Main(String[] args)
    {
        new QApplication(args);
        new Test2();
        return QApplication.Exec();
    }
}

Thanks again,
Jordan

On Thu, Feb 14, 2013 at 9:57 AM, Dimitar Dobrev <dpldobrev at yahoo.com> wrote:
>
>     Hello,
>
>     The Qt docs are a bit vague about whether addChild and similar functions
> change the ownership of the passed object. However, in the chapter for
> QTreeWidgetItem they do give the following:
>
> Items are usually constructed with a parent that is either a QTreeWidget
> (for top-level items) or a QTreeWidgetItem (for items on lower levels of the
> tree). For example, the following code constructs a top-level item to
> represent cities of the world, and adds a entry for Oslo as a child item:
>
>      QTreeWidgetItem *cities = new QTreeWidgetItem(treeWidget);
>      cities->setText(0, tr("Cities"));
>      QTreeWidgetItem *osloItem = new QTreeWidgetItem(cities);
>      osloItem->setText(0, tr("Oslo"));
>      osloItem->setText(1, tr("Yes"));
>
>     So you may try explicitly giving a parent to your items. I myself will
> test your example later today.
>
>     Regards,
>     Dimitar Dobrev
>
> ________________________________
> From: Jordan Miner <jminer7 at gmail.com>
> To: kde-bindings at kde.org
> Sent: Thursday, February 14, 2013 5:37 PM
> Subject: [Kde-bindings] Qyoto memory problem
>
> Hi,
>
> I'm having a problem that seems like a bug in Qyoto. When I run the
> following code, usually (not always) I see a tree with two items under
> the root item. When I uncomment the GC.Collect(), one or both of the
> items no longer appear. It seems like the sub-items are getting
> garbage collected after they are added to the root item, but before
> the root item is added to the tree. The root item isn't keeping them
> from being collected like it should.
>
> I also ran into another instance of an object being collected when it
> shouldn't be, but I'll post it later.
>
> I'm currently using the .NET Framework (not Mono) on Windows XP.
>
> using System;
> using System.Collections.Generic;
> using QtCore;
> using QtGui;
>
> class Test1 : QMainWindow
> {
>     public Test1()
>     {
>         QTreeWidget treeWidget = new QTreeWidget();
>         QTreeWidgetItem root = new QTreeWidgetItem();
>         root.SetData(0, (int)Qt.ItemDataRole.DisplayRole, "Root Item");
>
>         QTreeWidgetItem item = new QTreeWidgetItem();
>         item.SetData(0, (int)Qt.ItemDataRole.DisplayRole, "Item #1");
>         root.AddChild(item);
>         item = new QTreeWidgetItem();
>         item.SetData(0, (int)Qt.ItemDataRole.DisplayRole, "Item #2");
>         root.AddChild(item);
>         //GC.Collect();
>         treeWidget.AddTopLevelItem(root);
>
>         CentralWidget = treeWidget;
>         Show();
>     }
>
>     [STAThread]
>     public static int Main(String[] args)
>     {
>         new QApplication(args);
>         new Test1();
>         return QApplication.Exec();
>     }
> }
>
> Thanks,
> Jordan
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