Adding QListWidgetItem To QListWidget

Question

So I have a class SnapshotPanel : public QListWidget that I am trying to add a QListWidgetItem to dynamically, however it when ever I try I get a segfault. I have verified that my code to add the item is correct as I can add to the list when I construct my SnapshotPanel. However I cannot add to the panel when the code is called via signals and slot, insight into what I am missing would be apprecited.

Here is the constructor:

SnapshotPanel::SnapshotPanel(QWidget *parent):QListWidget(parent)
{

  this->setViewMode(QListWidget::IconMode);
  this->setIconSize(QSize(256,256));
  this->setResizeMode(QListWidget::Adjust);

  QIcon icon("icon.jpeg");
  QListWidgetItem *widget = new QListWidgetItem(icon,"Earth");

  this->addItem(widget);
}

So is there any reason I wouldn't be able to use the following code when called via signals and slots:

{
  QIcon icon("icon.jpeg");
  QListWidgetItem *widget = new QListWidgetItem(icon,"Earth");
  this->addItem(widget);
}

Are there multiple threads involved? Why are you subclassing from QListWidget? Where's the rest of the SnapshotPanel code? Is this Qt 4 or Qt 5? — Kuba hasn't forgotten Monica
What signal are you using? And where are you connecting it to the slot? — agold
When posting a question about a problem with code, please post a complete example that reproduces the problem, or at least post code that has the problem itself. All that you've shown is correct - and you yourself would have known that if you just copy-pasted code from your question into a fresh project and tried it out yourself. — Kuba hasn't forgotten Monica

user23573 user23573 · Accepted Answer · 2015-09-25T06:45:20

I think it should just work. "Slots are normal C++ functions" according the documentation.

If you are using multiple threads you need to look into the connection mechanism. Perhaps you need to use queued connections. You would change your connect statements from:

connect(button, &QPushButton::clicked, this, &MainWidget::on_button_clicked);

to

connect(button, &QPushButton::clicked, this, &MainWidget::on_button_clicked, Qt::QueuedConnection);

But read the official documentation here. A SO question (basically pointing you back to the documentation) is here.

Adding QListWidgetItem To QListWidget

1 Answers