Why does not QListWidget sort correctly?

Qingshui Kong

Hi everybody,

Could somebody give me some help?
I want to use QListWidget sortItems() function. I enabled sortingEnable. But I don't think the result is correct.
If I input items 1, 2, 1152, the result will be 1, 1152, 2. But I think the result should be 1, 2, 1152.

And if I test this code,
if("1" == "1152")
{
qDebug() << "'1' == '1152'";
}
else if("1" > "1152")
{
qDebug() << "'1' > '1152'";
}
else
{
qDebug() << "'1' < '1152'";
}
if("2" == "1152")
{
qDebug() << "'2' == '1152'";
}
else if("2" > "1152")
{
qDebug() << "'2' > '1152'";
}
else
{
qDebug() << "'2' < '1152'";
}
The output is
'1' < '1152'
'2' < '1152'

I think this is right.

So could somebody give me some advice?
Thanks in advance.

Bonnie

Do you know that you are comparing their memory addresses?
If you want to test the comparing, you should write like this

if(QString("1") == QString("1152"))

And the result is

'1' < '1152'
'2' > '1152'

That is how string comparision works.
It will not compare the number value...

One workaround to this is that do not use setText, but

item->setData(Qt::DisplayRole, 1151);

Qingshui Kong

@Bonnie Thank you very much.
You explained how string comparision works. That is correct. And I tested as you said. But in my opinion, I still think they should compare the length of each string. Let it alone.

At first my code is
ui->listWidget->addItem(QString::number(nNum));
ui->listWidget->sortItems();
It works. I can see the num in the listwidget.

But after I changed the code to
QListWidgetItem item;
item.setData(Qt::DisplayRole, nNum);
ui->listWidget->addItem(&item);
ui->listWidget->sortItems();
It doesn'tt work. I can't see anything.

VRonin

@Qingshui-Kong said in Why does not QListWidget sort correctly?:

But after I changed the code to
QListWidgetItem item;
item.setData(Qt::DisplayRole, nNum);
ui->listWidget->addItem(&item);
ui->listWidget->sortItems();

You were very close to the solution, you just have to create the QListWidgetItem on the heap instead of the stack otherwise it gets destroyed:

auto item = new QListWidgetItem;
item->setData(Qt::DisplayRole, nNum);
ui->listWidget->addItem(item);
ui->listWidget->sortItems();

JonB

@Qingshui-Kong said in Why does not QListWidget sort correctly?:

But in my opinion, I still think they should compare the length of each string.

Then you had better let the C++/Qt designers know you don't agree with the way string comparisons work.

Qingshui Kong

@VRonin Thanks. After I responded. I tried that. It worked.

Qingshui Kong

@JonB Maybe I just made a mistake. I just think I saw something like that.