I have a QComboBox with an underlying model. Sometimes the model gets a couple of hundred of items, which makes it very difficult to scroll through the combobox. Is it somehow possible to add a scroll bar to the QComboBox? This would help a lot because my items are sorted.
I have read that QComboBox should come with a scroll bar by default, but this is not true in my case on my linux system. Is this the case with windows?
Best regards
QComboBox uses an QAbstractItemView (by default a QListView I think) for its popup. It's possible to call view() to get that widget. Since QAbstractItemView descends from QAbstractScrollArea, you can use all features from that class to modify how you want the scrollbars to show up.
As an extra, you can change this view to another type. For instance I have used a QTreeView in the past since it fit better with the data.
Related
Qt's QMainWindow has a ability to dock windows derived from QDockWidget. It also would put one on top on the other if few of them are stacked, producing a tab bar. Whenever a QDockWidget's state changes a signal topLevelChanged() is emmitted. At this point I would like to get access to underlying QTabWidget to set an icon for a a newly added tab. How can I do it? My patience is over trying to dig the answer out from Qt's documentation and source code. Thank you in advance.
So icon I want to be on Contents/Index tabs.
Once at least one dockwidget has been tabified, the main-window will create a QTabBar to provide the dock-tabs. Each dock-area can have its own tab-bar. These tab-bars will become children of the main-window, so you can use findChildren() or children() to get references to them.
The main difficulty will be in finding which dock-widget belongs to which tab and in which tab-bar. If the dock-widget window-titles are all unique, you can just search using the tabText(). Otherwise, you might be able to use the tabData(), which Qt sets internally to a quintptr from the dock-widget.
Once you have the correct tab, you can of course use setTabIcon() to add your icon. But note that every time a dock-widget is untabified or moved to another tab-bar, the icon will be lost.
Using Pyside, but a general Qt question:
I am building a Qt app with a controlling QMainWindow. From this window the user can open other QMainWindows (or QDialogs) and from some of those she can open more. The user is intended to think of the first QMainWindow as "the app" and the others as lots of different views on more or less the same data.
So I'd like all the windows to be independently stackable so the user can set up the screen to their own requirements. In particular I want the user to be able to bring the first QMainWindow on top if wanted. But I don't really want each window to have its own task bar entry (though I can live with that). Also I would like them to minimise and restore together, and I would like them all to close when the first main window closes.
If I parent them all on the first mainwindow it works nicely except they stay on top of it which is not what I want.
Instead I have it kind of working by making them all independent with parent = None. Then I register them all with the main window and close them all when it closes. But this makes them a bit too independent - they minimise separately and have their own task bar entry.
Am I missing some obvious fix to this? Is there any easy way (a flag?) to stop the children staying on top of the parent?
Or is there some UI guideline that I am breaking by desiring this?
Or is there a cleaner design somehow? I thought of adding a dummy parent that they could all descend from but maybe that's messy. Would that parent need a visual presence? I wouldn't want that.
Suggestions?
You can have as many QMainWindows as you want, or parentless QWidgets. I think the best way to handle your situation is to create your own pseudo parent-child relationship like this:
In your QMainWindow subclass, store a QList of all the QWidgets you want it to manage. Then, again in your QMainWindow subclass, reimplement methods such as QWidget::closeEvent(), QWidget::hideEvent() (for when the window is minimized), and QWidget::showEvent() (for when it is restored) so that it also closes, hides, or shows all of the widgets in its QList. Make sure to also delete them in the QMainWindow subclass's destructor. Now, whenever you create a sub-window, pass the main window a pointer to it not as a normal QWidget child, but just so that it can be added to the main window's QList of QWidgets to manage. E.g.:
MainWindowSubclass::addPseudoChild(QWidget *pseudoChild)
{
myListOfPseudoChildren.append(pseudoChild);
}
Another alternative that hasn't been mentioned yet is populating a QMdiArea with QMdiSubWindows. It doesn't do exactly what you asked for, but it's a pretty clean design nonetheless.
So I thought I would add what I eventually settled upon. This was particularly inspired by the comments of #leemes (Thanks - good stuff) and a little experimentation of my own.
I used the code attached here DetachTabExample
to develop a "Detachable Tab" widget and tab bar. This allows tabs to be dragged outside the main window when they become independent windows. Then if closed they return to the tab bar.
Then I placed all my content in the QMainWindow but in separate tabs. The users can drag the ones they want out on to the other monitor. Seems to be working fine. There are still some extra windows that I have floating but it has cut down the clutter and clarified the structure.
My custom QListView has delegates to paint the items. I'd like to add a live control to some of the row items (like a QLineEdit), that'll always be present in the row and will automatically scroll correctly with the list.
Since items are not widgets, I cannot assign a control to be a child of an "item", thus scrolling will leave the control in its fixed spot within the QListView widget.
Is there another way?
Is that even possible?
Normally the edit widget is created (and positioned) by the delegate when an QEvent::EnterEditFocus event occurs then destroyed when a subsequent QEvent::LeaveEditFocus occurs and the data is sent back to the model. The delegate should then repaint with the new model data.
Could you expand on what you mean by a "live" control?
Why would you want to have an edit widget constantly open? I think a better way to do this would be to create a delegate which paints the normal view (i.e. for Qt::DisplayRole) in a way which you want. Assuming you create your subclass view correctly, the delegate should still update when the model changes.
If you really want to do what you're asking though, I suspect you might be able to by:
creating your own item delegate (subclassing QAbstractItemDelegate)
reimplement createEditor() to use a QLineEdit
then use the delegate's updateEditorGeometry()
Have a read of the Delegate Classes section of the Introduction to Model/View Programming though first. The Spin Box Delegate Example and Pixelator Example are worth studying too if you haven't already.
This is driving me nuts. I have a custom menu class that, when set visible, shows a list of items located in a particular folder. When a hardware button is pressed, my application gets the latest list of items, populates the menu with them, and returns.
The menu displaying these items uses a QListWidget filled with custom widgets. Each of the widgets contains one or more QLabels in a horizontal layout, and is created at the time the menu is shown. In order to adjust the text displayed based on the menu width available, I need to get the size of the QLabel AFTER it has been resized according to the layout, but before the menu becomes visible to the user. The problem is, my layout does not get updated until all of the functions constructing my list return.
I have tried QApplication::ProcessEvents() and the layout update functions, but none of them have updated the values of my QLabels before returning. I can set a QTimer when the button is initially pressed, and have it show the menu, update the items, and stop itself, but that seems like a terrible solution.
Any help would really be appreciated! I've spent most of a day on this.
Marlon
I had this exact problem and could not find an answer anywhere on the Internet. Calling Layout.update(), Layout.activate(), or widget.adjustSize() (all suggested in various places) all did not work.
I had a widget with a vertical layout that I wanted to add a QLabel to and then immediately use the size of the QLabel.
The only thing that worked reliably was
layout->addWidget(myLabel);
myLabel->show();
size = myLabel->size();
It would seem that layouts will just not recalculate until you either return from a function and allow the Qt event loop to progress or manually call show() yourself.
How to update a QLayout and get the new dimensions before returning?
Don't. You're not meant to do that. It'll drive you "nuts" because you're doing it backwards. Layout updates are handled asynchronously from the event loop. Instead of getting layout dimensions right away, set yourself up to be part of the system. Some options are:
Implement a custom widget that will interact properly with the layout, growing to fill the available width of the layout. Perhaps all you need is a size policy and a way to elide text?
Make a custom layout that takes the special properties of your use case into account.
You want to call QWidget::adjustSize() on your parent widget. This will force the layout recalculations.
Have you tried using layout()->update(); ?
I've tried many but nothing works for me on Qt 5.15.
Only invented little patch - create timer and get size after 20 msec:
QTimer::singleShot(20, this, [this]
{
const auto height = myLayout->contentsRect().height();
// ...
});
I am creating my first app in QT and wanted to design a list. The listitem has two texts and one icon.
The problem is, i cant find any example or helping material, Only helping link i found is : Customize QListWidgetItem but i dont understand it. Although i have the same problem which this links points to...
What i understand is, i have two options:
1- Customize QListWidgetItem to use with QListWidget
2- Make some delegate to use with QListView
I was hoping to get started with option 1. Now in the link, some reply talks about "myItem" which is taking 2 texts as input. I want to know the implementation of "myItem".
In the link you posted, MyItem is just a normal QWidget. This means that you can create a widget in Qt Designer and then set that new widget you created as the widget that the QListWidgetItem should use for display. In the above example, MyItem takes two strings because there is a vertical layout with two labels in it (that's my assumption at least).
You should also note, and is discussed in the above link, that taking the approach of setting an item widget to use for every item in the list is an expensive thing to do in terms of performance and memory consumption. Because a QListWidget is a QListView, you can set an item delegate on it just like any other view and come out with a lighter weight solution (one instantiation of class vs. one instantiation for every item in your list)