QListWidget item editing

[JonB]

Qt 5.7. I am using a QListWidget, where its QListWidgetItems have the ItemIsEditable flag. At the moment, at least, the items are the standard strings, with the editor being the built-in QLineEdit, i.e. I am not providing my own editor.

I need to know when the user starts editing an item and when he has finished editing an item (e.g. while editing, buttons I have attached to the list widget for adding/deleting items should be disabled).

Call me dumb, but I cannot see signals (or overridable) functions for these?

• The only signal I can see for starting out is QListWidget::itemDoubleClicked. Is that the only way to start editing, and that's what I'm supposed to use?

• Worse for finished editing. There is QListWidget::itemChanged, which seems great if the user makes a change and clicks elsewhere or whatever --- I receive that one.

• But what if the user does not change the item? He might do anything, e.g. click some other widget, tab away, I have no idea. How do I know what the QLineEdit seems to know when it takes the user out of editing mode and no change has been made?

[JonB]

@VRonin
Well, I followed your principle of having the QStyledItemDelegate emit signals with the QModelIndex as a parameter.

I diverged from yours slightly. Given that I'm now overriding destroyEditor() so as to access the index, it seems to me that I might as well be consistent and override createEditor() for beginning editing. So the following two overrides:

class JEditableListStyledItemDelegate(QtWidgets.QStyledItemDelegate):
    # class variable for "editStarted" signal, with QModelIndex parameter
    editStarted = QtCore.pyqtSignal(QtCore.QModelIndex, name='editStarted')
    # class variable for "editFinished" signal, with QModelIndex parameter
    editFinished = QtCore.pyqtSignal(QtCore.QModelIndex, name='editFinished')

    def createEditor(self, parent: QtWidgets.QWidget, option: QtWidgets.QStyleOptionViewItem, index: QtCore.QModelIndex):
        editor = super().createEditor(parent, option, index)
        if editor is not None:
            self.editStarted.emit(index)
        return editor

    def destroyEditor(self, editor: QtWidgets.QWidget, index: QtCore.QModelIndex):
        self.editFinished.emit(index)
        return super().destroyEditor(editor, index)

The above seems to give me fairly reliable signals for what I want, e.g. disable other buttons for doing things to QListWidget (add row, delete row) while the user is editing a row.

Seem reasonable to you? Thanks for all your input.

[VRonin]

That's because it's handled by the delegate.
Subclass QStyledItemDelegate

class SignalItemDelegate : public QStyledItemDelegate{
Q_OBJECT
Q_DISABLE_COPY(SignalItemDelegate)
public:
explicit SignalItemDelegate(QObject* parent = Q_NULLPTR):QStyledItemDelegate(parent){
QObject::connect(this,&SignalItemDelegate::closeEditor,this,&SignalItemDelegate::editFinished);
}
void setEditorData(QWidget *editor, const QModelIndex &index) const Q_DECL_OVERRIDE{
editStarted();
return QStyledItemDelegate::setEditorData(editor,index);
}
Q_SIGNALS:
void editStarted();
void editFinished();
};

And then call something like:

SignalItemDelegate* delegate = new SignalItemDelegate(listWidget);
QObject::connect(delegate,&SignalItemDelegate::editStarted,[](){qDebug("edit started")});
QObject::connect(delegate,&SignalItemDelegate::editFinished,[](){qDebug("edit finished")});
listWidget->setItemDelegate(delegate);

[JonB]

@VRonin
Ah ha! Your famous QStyledItemDelegate, which I have steadfastly not got into so far! OK, let me go set this up and see where I get. I may have further questions for what I'm trying to actually achieve fully (the above is just one part), I'll come back to your expertise on that if I may....

[dheerendra]

Did you get a chance to look other set of signals like.

currentItemChanged(..)
clicked(..)
entered(..)
pressed(..)

[JonB]

@dheerendra
Yep, I looked through all those. None of them pick up, e.g., terminating editing, at least, so no good....

[dheerendra]

terminatingEditing has to be custom. You have no choice other the your own delegate :)

[JonB]

@dheerendra
Yep, that's fine, as I wrote to @VRonin above, I am presently having a go at his code (converted to Python/PyQt!) to get me going....

[DyraSan]

Hey, I am newbie

and I want to know how to edit a QListWidget item without removing it to edit and adding back?

thanks,

Kissanime

[VRonin]

listWidget->item(i)->setData(role,data);

[JonB]

@VRonin
OK, I have come up with the basics which I believe emulates/corresponds to your C++ as best I can. I now have a further question about something which you don't do in your example which I would like.

First, I'll paste the guts of my Python/PyQt code. You'll see it's rather different in signals/slots/emits. This may help or hinder, I don't know, feel free to ignore if that's best.

class JEditableListStyledItemDelegate(QtWidgets.QStyledItemDelegate):
    # class variable for "editStarted" signal
    editStarted = QtCore.pyqtSignal(name='editStarted')
    # class variable for "editFinished" signal
    editFinished = QtCore.pyqtSignal(name='editFinished')

    def __init__(self, parent: QtCore.QObject=None):
        super().__init__(parent)

        self.closeEditor.connect(self.editFinished)

    def setEditorData(self, editor: QtWidgets.QWidget, index: QtCore.QModelIndex):
        self.editStarted.emit()
        return super().setEditorData(editor, index)


class JEditableListWidget(QtWidgets.QListWidget):
    # class variable for "editStarted" signal
    editStarted = QtCore.pyqtSignal(name='editStarted')
    # class variable for "editFinished" signal
    editFinished = QtCore.pyqtSignal(name='editFinished')

    def __init__(self, parent: QtWidgets.QWidget=None):
        super().__init__(parent)

        styledItemDelegate = JEditableListStyledItemDelegate(self)
        styledItemDelegate.editStarted.connect(self.editStarted)
        styledItemDelegate.editFinished.connect(self.editFinished)
        self.setItemDelegate(styledItemDelegate)

The above "works". The JEditableListStyledItemDelegate emits its own editStarted/Finished signals. The JEditableListWidget "redirects" those signals to its own editStarted/Finished signals, for the outside world to slot onto. So far so good?

Now, if you look at a QListWidget signal for an item like http://doc.qt.io/qt-5/qlistwidget.html#itemChanged, its signature is QListWidget::itemChanged(QListWidgetItem *item). Hence it sends to the outside world a parameter of the QListWidgetItem which has been changed. My editStarted/Finished signals should do the same.

Now I get stuck as to how I'm supposed to do that.

I start by changing my JEditableListWidget signals to:

class JEditableListWidget(QtWidgets.QListWidget):
    # class variable for "editStarted" signal, including item
    editStarted = QtCore.pyqtSignal(QtWidgets.QListWidgetItem, name='editStarted')
    # class variable for "editFinished" signal, including item
    editFinished = QtCore.pyqtSignal(QtWidgets.QListWidgetItem, name='editFinished')

The extra first parameter of QtWidgets.QListWidgetItem declares the signal as forwarding the item as a parameter.

Now how do I pass that? I believe that (a) I will need a lambda for the signal and (b) I need to know what item is being edited. I think where I had:

styledItemDelegate.editStarted.connect(self.editStarted)

I now need something like:

styledItemDelegate.editStarted.connect(lambda: self.editStarted(someItemWidget))

[Actually I suspect it might be more like:

styledItemDelegate.editStarted.connect(lambda: self.editStarted.emit(someItemWidget))

]
Could you tell me:

• Is this how you would do it in C++ (e.g. with a lambda)? (If not, I may be doing it wrong.) Could you show me your C++ for how you would do this and I will attempt to figure it to PyQt? (Also, I believe your code omitted an emit because I know that's a NO-OP in C++; but could you include it wherever it should be, because in PyQt you can see we have to use emit as a function.)

• How do I calculate what the someItemWidget will be, from inside my JEditableListWidget?

[VRonin]

It's actually super easy.
In the delegate:

• add an argument of type QtCore.QModelIndex to the signals.
• remove self.closeEditor.connect(self.editFinished)
• change self.editStarted.emit() to self.editStarted.emit(index)
• add

def destroyEditor(self, editor: QtWidgets.QWidget, index: QtCore.QModelIndex):
        self.editFinished.emit(index)
        return super().destroyEditor(editor, index)

Now in JEditableListWidget you can connect a slot that accepts a QtCore.QModelIndex. To find the corresponding QListWidgetItem you can just call item(index.row())

[JonB]

@VRonin
TVM. I'll implement next week. You're passing the QtCore.QModelIndex available in the JEditableListStyledItemDelegate class up the signal chain to indicate which QListWidgetItem was acted upon. I thought the JEditableListWidget class would know which item in the list was being edited, but seemingly not?

[JonB]

@VRonin
Well, I followed your principle of having the QStyledItemDelegate emit signals with the QModelIndex as a parameter.

I diverged from yours slightly. Given that I'm now overriding destroyEditor() so as to access the index, it seems to me that I might as well be consistent and override createEditor() for beginning editing. So the following two overrides:

class JEditableListStyledItemDelegate(QtWidgets.QStyledItemDelegate):
    # class variable for "editStarted" signal, with QModelIndex parameter
    editStarted = QtCore.pyqtSignal(QtCore.QModelIndex, name='editStarted')
    # class variable for "editFinished" signal, with QModelIndex parameter
    editFinished = QtCore.pyqtSignal(QtCore.QModelIndex, name='editFinished')

    def createEditor(self, parent: QtWidgets.QWidget, option: QtWidgets.QStyleOptionViewItem, index: QtCore.QModelIndex):
        editor = super().createEditor(parent, option, index)
        if editor is not None:
            self.editStarted.emit(index)
        return editor

    def destroyEditor(self, editor: QtWidgets.QWidget, index: QtCore.QModelIndex):
        self.editFinished.emit(index)
        return super().destroyEditor(editor, index)

The above seems to give me fairly reliable signals for what I want, e.g. disable other buttons for doing things to QListWidget (add row, delete row) while the user is editing a row.

Seem reasonable to you? Thanks for all your input.

[VRonin]

@JonB said in QListWidget item editing:

Given that I'm now overriding destroyEditor() so as to access the index, it seems to me that I might as well be consistent and override createEditor() for beginning editing.

Only doubt I have is if the delegate recycles the editor. Try going from editing 1 cell to editing another one directly and see if both create and destroy are called or it just calls setEditorData

[JonB]

@VRonin
OK, thanks! You should have said that concern was why you had overridden different/"inconsistent" methods, I had no idea why! Tried with direct click to edit another item, all is well, does call destroy and then create.

So I shall mark what I did as the solution to my original question. TVM.

P.S.
Your Xmas hat looks good. But a lot of others are also wearing them...! :)

[mrjj]

@JonB said in QListWidget item editing:

Your Xmas hat looks good. But a lot of others are also wearing them...! :)

Well that is is on purpose :)

[VRonin]

@JonB said in QListWidget item editing:

Your Xmas hat looks good

All credit goes to @mrjj