How to use QTableWidget::setCellWidget() to set a widget such as a QComboBox and do the further handling?

ailika

@JonB Im still confused. Even if I use new style signal and slot and use lamba to pass extra information. But the widget who send the signal is combo which is a standard widget, which is to say it can't send the "row/column" information I wanted. It seems I still have to subclass combo.

JonB

@ailika said in How to use QTableWidget::setCellWidget() to set a widget such as a QComboBox and do the further handling?:

is to say it can't send the "row/column" information I wanted

You can pass that at the time you are doing the connect(). Since you create setCellWidget(i,0,comBox) something like:

connect(comboBox, QOverload<int>::of(&QComboBox::currentIndexChanged),
        this, [=](int index) { tableComboIndexChanged(i, 0, index);  });

void MainWindow::tableComboIndexChanged(int row, int column, int index)
{
}

ailika

I'm sorry I'm not familiar with advanced usage of c++, such as lamba. So I don't understand the the code.
Do you mean when I use connect, I can set a fixed inforation and when I receive the signal in the slot function I can get the information? If it is so, it is a better method than subclassing the combo box. But currently it seems I can just use subclassing method. Learning lamba is not a prority.
In fact, I'm a new QT learner also. I have just read a book and haven't done much practice.

I'm very confused with my data presentation. It seems there are several ways, it seems hard to choose.
If I use standard QTableWidget， I think I need to process the data in the parent widget, don't I? So I need to know the row and column badly. This is the simple way, but it seems not so "tidy".
If I use the model/view structure, I can process the date in the self-defined model, maybe I don't need this information that much. But the model/view structure is very complicated.
So what's the better way to present the data?

JonB

@ailika said in How to use QTableWidget::setCellWidget() to set a widget such as a QComboBox and do the further handling?:

I'm sorry I'm not familiar with advanced usage of c++, such as lamba. So I don't understand the the code.

I am sorry of you don't understand. All you should have to do is copy that code, provided it's correct, which I think it is. And read up on C++ lambdas if you want to understand it.

So I need to know the row and column badly.

If this is indeed true then you should be using the lambda as the only way to pass extra parameters to the slot I showed you. That's what's required to send the extra row/column information.

Otherwise you're on your own. If you want to do it with your sub-classing that's up to you.

VRonin

Don't reinvent the wheel, setCellWidget is the wrong tool for the job (as it is in 99.9% of the cases). You should use a delegate, have a look at https://wiki.qt.io/Combo_Boxes_in_Item_Views

ailika

@JonB Thank you very much. I think I will learn lamba later. I just want to focus on the table widget now

ailika

@VRonin said in How to use QTableWidget::setCellWidget() to set a widget such as a QComboBox and do the further handling?:

Views
I m leaning the table widget. Firstly , I use the sellWidget to try it out, since it's very simple. After this, I will try to use the delegate model view method, and see which one suits most. I think its the most complicate part in QT.

ailika

I tried this method, it works. But there is a problem: When the table shows up, the combox doesn't show, I have to double click the item then the combox shows. I have tried spinbox, it does not show up automatically too. How to fixe this problem?

JonB

@ailika said in How to use QTableWidget::setCellWidget() to set a widget such as a QComboBox and do the further handling?:

I have to double click the item then the combox shows.

Have a look at your setting for editTriggers. If your behaviour is QAbstractItemView::DoubleClicked only you can change that.

ailika

But even if I use QAbstractItemView::AllEditTriggers, I need to single-click to make the item show.

JonB

@ailika
That is correct. The code you copied which @VRonin referred you to produces a combobox only when the user wishes to edit a cell. Otherwise the cell just shows the current value. Little point in showing a combobox when you're not editing something. When you have 10,000 rows in your table view @VRonin is trying to save you from having 10,000 comboboxes present all the time, which is "expensive/inefficient".

ailika

I haven't think of this problem. If I have 10000 combox, I will have to create 10000 objects which will "swallow" the RAM. This indeed is a problem. So this is his really purpose, not a defect?

In fact, I don't use the table to do some data process which may contain thousands of data. I need only 250 rows and need it to be displayed.
Currently, I think the createEdit method can't work. I think I should use 'QStyleOptionComboBox' instead, am I right? But this really difficult, I haven't seen any complete example in the network. Currently I can only display a text in the combox item, but it can't popup. It seems that I should study QStyle function first and see whether I can solve my problem.

JonB

@ailika
Even 250 comboboxes is quite a lot.

Anyway, I don't know what doesn't work for you. If you follow the code in @VRonin's Combo Boxes in Item Views you should find:

Initially all items are displayed with their current values, no comboboxes.
Then you click or double-click in a cell and it turns into a combobox.
Then you click on the combobox to get the popup and do the editing.
Then you click away or whatever and it reverts to the text value.

ailika

@JonB
250is quite alot? I have seen other similar application who has 250 combox. But they ard made by MFC and c#. so it's not unreasonable quantity.
I have used the code and it works like you said.
But what I need is to to display them initially not display on edit. The display on edit way just don't fit into the application. If I cant solve it even by QStyle, I will use the setCellWidget way or just do not use the combobox. Just use a dialog to edit the date and use the table to dislpay text(the dialog is destined to be used what ever method I use.)

JonB

@ailika
In that case: either it's possible to have a delegate for normal, non-edit viewing which "looks like" a combobox --- I don't know if you can do that, as you say maybe QStyleOption something --- and then it has to change into a real combobox on click. Or, also as you say, go back to your preferred setCellWidget(). In which case I showed earlier how you can access the row/column, or the actual combobox, in the slot, which is what you originally asked for.

ailika

@JonB Thank you for your answer. Your answer is one way . I will start a new question if I cant do the QStyle function.

ailika

@JonB But can I ask why setCellWidget is usually not good?

JonB

@ailika
@VRonin is the one who guided you away from setCellWidget()/setIndexWidget(). Look at his signature! :)

I backed him up, pointing out to you one disadvantage of memory/efficiency.

He is generally correct. However, I am not necessarily on the crusade he is on! :) I answered your question initially for the setCellWidget() you asked about. For 250 comboboxes I personally would use his styled item delegate. But I am not going to die in a ditch if you are aware of this but still wish to use setCellWidget() in your own code. Just don't tell him I said this to you.... ;-)

ailika

@JonB Thank you both! It seems this form is very good. There are people there answering my question. And it seems that qt is somehow well surpported.

ailika

@JonB I have been studying the QStyle's help documentation theses days. It really makes me angry that I find the sentence "The list that pops up when the user clicks on the combo box is drawn by a delegate, which we do not cover in this overview. " How to display the important popup menu is not described!! And I have alreay displayed the others quite well.
Do I need to write the hard code for the whole popup window all my self? I don't see it very necessary, since qt has alreay paint the combo box. I think it will be a repeated work if I write the paint code myself.