Combining classes - append class to QMainWindow

Chris Kawa

QMainWidnow doesn't have any central widget by default, so do you actually have a central widget? i.e. does centralWidget() return a non-nullptr ?
From the picture I see you don't have one added in code so have you added it in the designer?
If so - does it have a layout? i.e. does centralWidget()->layout() return a non-nullptr?

Anonymous_Banned275

Yes, I did build QMainWindow using QtDesigner GUI and it does have centralWidget. I'll try to just replace it with the QMdiArea.
I did some more reading on QMainWindow and it looks as I COULD replace default centralWidegt with QDock and then add centralWidget "inside" QDock.
It is getting too complicated , but it may be the best final solution.

Chris Kawa

@AnneRanch That doesn't sound right.
QMainWindow has an internal layout implementation and has an API that allows you to add one widget as a central widget, a widget as a toolbar, menubar and a bunch of QDockWidgets. Sorry to question you, but it really look s like you just don't have a central widget. It sounds like you want your mdi area to be the central widget so just setCentralWidget(mdiarea). If that's really really not the case could you post a screenshot of your widget hierarchy in the designer?

Anonymous_Banned275

I did replace the default centerWidget and it works "BETTER".
Now I have status bar , but Mdi still writes over menubar

   MdiArea *mdiarea = new MdiArea();
    if(centralWidget())
        std::cout <<"TOK centralWidget()  " <<std::endl;
    else
         std::cout <<"FAILED centralWidget()  " <<std::endl;
     setCentralWidget(mdiarea);

Chris Kawa

Ok, you do have a central widget in designer but it doesn't have a layout (the red crossed circle indicates that), so centralWidget()->layout() is null. That's why it crashed.

Couple of options:

(That's the one I'd recommend) Delete the central widget in designer and set mdiarea to be it from code:

setCentralWidget(mdiarea);

Add a layout to your central widget in designer and then you can do

centralWidget()->layout()->addWidget(mdiarea);

Add the layout from code and add a widget to it:

QVBoxLayout* central_widget_layout = new QVBoxLayout(centralWidget());
central_widget_layout->addWidget(mdiarea);

but Mdi still writes over menubar

I don't think it does. You just don't have anything in the menubar so it doesn't show up. It will show up once you add some menus or actions to it.

Anonymous_Banned275

Thanks.
You solved THREE "problems" in one post !
I did not realize default QMainWindow form does not have a layout.
I did not actually know what is "THE LAYOUT" and how it fits into the scheme of things.
And I'll add some stuff to menu bar to see it .

Great progress, but I need to fine tune it by adding the "rotten" btscanner dialogue as QDock next...

SGaist

Hi,

@AnneRanch said in Combining classes - append class to QMainWindow:

I did not realize default QMainWindow form does not have a layout.

In fact it does have one and that's why you got the error message when trying to use it. QMainWindow's layout is "protected" because it's it that provides support for dock widgets toolbars etc.

Anonymous_Banned275

@Chris-Kawa said in Combining classes - append class to QMainWindow:

but it doesn't have a layout (the red crossed circle indicates that)

OK, clarification needed.

Even AFTER adding "form layout" I still have "red crossed circle" showing in the icon. No errors.

Having presence or being "protected" seems to be TWO different properties.

So which one "is causing the problem" encountered?

Anonymous_Banned275

Expanding on the original post.
Adding tab class to MainWindow by setting new centralwidget bypasses the missing / private "layout" . That works as desired.

After that, similar process needs to be done "dowstream" - add QDialog to Tab class. Here the QDialoig does not have "centralwidget" to be replaced.
So it is back to "layout" which does not exists or is private.

Or I can go back to original - replacing QDialog with QWidget.
Prefer no to do so - woudl have to convert more QDialogs to QWidgets.

Any different solution , similar to centrawidget / layout , would be appreciated.

JKSH

@AnneRanch said in Combining classes - append class to QMainWindow:

Here the QDialoig does not have "centralwidget" to be replaced.

It doesn't indeed. QMainWindow is a special widget with many regions including the "central" region. No other widgets have this structure. See the documentation at https://doc.qt.io/qt-5/qmainwindow.html :

QMainWindow layout

So it is back to "layout" which does not exists or is private.

...

Any different solution , similar to centrawidget / layout , would be appreciated.

Just like you call setCentralWidget() on QMainWindow, you can call setLayout() on plain "container" widgets like QWidget, QDialog, and QGroupBox.

add QDialog to Tab class

Can you explain your rationale for doing this?

A dialog is designed to be a separate pop-up window. A tab widget is for "embedding" other widget inside an existing window. They have opposite goals.

JonB

@AnneRanch
Going back for a moment to your earlier screenshot, and something @Chris-Kawa said about it. When using Qt Designer and you look at that "Object/Class" window showing your widget hierarchy: anywhere there you might see any widget you have added showing that "red-crossed-circle no-entry sign" on the widget. That indicates you should right click on that widget and add a layout to it. Without that, your widget layout is liable to be wrong.

Anonymous_Banned275

Well , not sure if the group wants to continue this discussion.
Been chastised for "reinventing wheel ", using stuff DIFFERENTLY than usual etc, Really do not want to repeat that, so let me leave WHY I am doing this alone. Maybe later...

I prefer KISS, so my initial approach was to use QtCreator and build , using QtDesigner , base QMainWindow class.
I did try QtCreator examples "Application" but it does not use Ui and I was not comfortable modifying "Application" example to fit my goal.

However, the QMainWindow class build GUI "form" does not indicate , with the exception (red cross ) I just learn during this discussion, that "layout" is mandatory.

That is still unresolved , because AFTER I manually add , using QtDesigner, " form layout " - the "red cross" is still there.

As far as using code to reset "centralwidget" I am questioning the necessity of having "layout" - the application GUI works with no specific layout, just "free hand" , which to me makes sense.
( Not sure of advantage of using "form layout" during development - machine second-guessing the location of widgets or vice versa)

BUT it looks as adding new QWidget to QMainWindow WITHOUT having "layout" is an issue.
( this format is awkward - I cannot see the previous post to intelligently reply to it )

Now back to adding QDialog.
I did try to add "layout" using code , but could not find how to code it . I got as far as QLayoutItem. I am still learning to navigate QtCreator.

 ui->tab->setLayout(????); // test add layout to first tab

PS
Here is another, unconventional approach , to similar task
https://stackoverflow.com/questions/23676283/splitting-qt-forms-between-multiple-ui-files
Just to point out I am not the only crazy one.

Anonymous_Banned275

@JonB
Do I understand it correctly - adding "layout" to "centralwidget" is not enough to remove the "red cross" ?
"layout" needs to be added to any widget "bellow" the "centralwidget".

That is pretty minor issue - still looking for an answer why "layout" needs to be used at all when adding widgets in code.

Chris Kawa

Layouts are sort of a geometry managers for child widgets. When you resize a widget its layout takes care of moving and resizing the children to accommodate new parent size.

A widget has either no layout or exactly one. This is indicated via that icon we talked about. If a widget has no layout its children sizes and positions are not automatically adjusted and can overlap. In such case you are responsible for manually calling setPos, move, resize, setGeometry or any other similar functions to set a correct child geometry. Layouts are a way of automating this tedious task. If a widget has a layout set it will react to the widgets resizeEvent and adjust children according to the layout's type. For example a QVBoxLayout will place children one under the other. QGridLayout will place them in a grid etc.

Now for a little confusing part. You said you added a layout and it didn't remove the red circle. If you did that by dragging a layout from the toolbox on the left like you would with a button or a frame then you didn't set a layout on the widget. You added a new widget with that layout set, so what you have is the original widget, still without layout and a child with that layout.

The option to set a layout on a widget is either in the right click menu under the "Lay out" sub-menu or on the toolbar (icons with dots, horizontal and vertical bars). An important note is that designer does not allow to set a layout on a widget that has no children (because it's usually not what you want anyway) so if you don't have any children those options will be grayed out.

If you want to do that anyway you can workaround it with these steps:

add any child widget to the widget you want the layout set on (button, frame or whatever)
select the widget you want the layout to be set on
use either the right clik menu or the toolbar icons to set a layout (vertical, horizontal or grid)
remove the child widget you added previously

This is not something you usually do though. Usually you either add children and set layout in the designer or do both of those from code.

Pl45m4

@AnneRanch said in Combining classes - append class to QMainWindow:

is not enough to remove the "red cross"

It is, but if you do this in code, you will still see the red cross in QtDesigner, because your coded layout applies at run-time.

Every widget or widget container can / should have a layout. Otherwise its content is floating around and it will produce other unwanted behavior, in terms of size (resizing) and position (while moving).

So every new QMainWindow has its centralWidget, which is empty and has no layout set, per default. You could either add content to it, by drag'n'drop, using QtDesigner and then right click centralWidget -> Layout -> Then pick layout of your choice or you set a layout by using your code, then "grab" that layout again and add widgets (content)

QHBoxLayout *cW_Layout = new QHBoxLayout;
this->centralWidget->setLayout(cW_Layout);

// To access your CW or its layout, do
centralWidget->layout()->addWidget(  WIDGET_TO_ADD );

// Ofc you can also populate your layout first before adding it to centralWidget

Anonymous_Banned275

I need to restate - I did change / add layout in QtDesigner to observe the red cross persistence.

I did not do that in code.

As far as layout "automatically " do resizing - I am still in basic app development , hence I am happy camper when I see expected "static" results , I am not in position to move / resize things around at this stage.
However, it is nice to know WHY to use layout in future, even it is not of my primary concerns for now.

Cheers

Anonymous_Banned275

@Pl45m4 said in Combining classes - append class to QMainWindow:

@AnneRanch said in Combining classes - append class to QMainWindow:

is not enough to remove the "red cross"

It is, but if you do this in code, you will still see the red cross in QtDesigner, because your coded layout applies at run-time.

Every widget or widget container can / should have a layout. Otherwise its content is floating around and it will produce other unwanted behavior, in terms of size (resizing) and position (while moving).

So every new QMainWindow has its centralWidget, which is empty and has no layout set, per default. You could either add content to it, by drag'n'drop, using QtDesigner and then right click centralWidget -> Layout -> Then pick layout of your choice or you set a layout by using your code, then "grab" that layout again and add widgets (content)
QHBoxLayout *cW_Layout = new QHBoxLayout;
this->centralWidget->setLayout(cW_Layout);

// To access your CW or its layout, do
centralWidget->layout()->addWidget(  WIDGET_TO_ADD );

// Ofc you can also populate your layout first before adding it to centralWidget

This post is pretty much repeat of what was already said.
This is not criticism, just a statement of fact.

While applying similar approach in "layout-less" QDialog , as fas as QMianWindow" sees it, I have opted to use "promotion" and it works as desired.

Of course the "promoted" form has "layout" already.
I hope that makes sense.

Pl45m4

@AnneRanch said in Combining classes - append class to QMainWindow:

This post is pretty much repeat of what was already said.

If you look at the time stamps of @Chris-Kawa 's and my post, you will see that they are just 2-3mins or so apart. The moment when I started typing, there was no response... So we both wrote our replies at the same time :)

Anonymous_Banned275

I think I have painted myself into a corner.

I have QMainWindow with class member BT_TabWidget
This part works and I can verify the “connect” too

 BT_TabWidget *BT_tab = new BT_TabWidget(this);
  setCentralWidget(BT_tab);
  connect (BT_tab,
           SIGNAL(tabBarClicked(int)),
           this,
            SLOT(MainTestFunction())
           )
           ;

In the BT_TabWidget I have promoted “tab” QWidget to
DeviceDiscoveryDialog - QDialog class
This part also works and I can actually retrieve / list bluetooth devices.
DeviceDiscovwryDialog class has a member class QBluetoothDeviceDiscoveryAgent
instantiated as
discoveryAgent = new QbluetoothDeviceDiscoveryAgent();
discoveryAgent does all the dirty work and it does it well , so far.

Here is MY problem , basically while trying to monitor the working application progress.

I cannot use discoveryAgent , have no access to it , as source for “connect”
I should be able to get intelisense to accept / provide the following
BT_tab→discoveryAgent....
But it gives no "discoveryAget" option.
I cannot figure out HOW to include SLOT (QMainWindow(….) ) ,
in “connect” . Again intelisense is of no help and I am not sure if the #1 problem is the cause.
( I did try &app (main application) - no go )

I am using "discoveryAgent" within the QbluetoothDeviceDiscoveryAgent to track the bluez "library" and just like to extend it to the main "status bar". It worked prior to implementing the promotion scheme.

I am sorry to drag this discussion, but I keep running into these issues in the process.

Anonymous_Banned275

@AnneRanch Here is a thought.
Since promotion works I suspect that promoting QWidget "tab" to "DeviceDiscoveryDialog" is assigning a pointer to the class.
I do not know that pointer, neither does Qt and its intellisence.
Not having access to the unknown pointer I obviously do not have access to "DeviceDiscoveryDialog" variables / methods .

So it is back to QtCreator interaction with QtDesigner - an annoying and BIG issue since I first started looking into Qt.
Perhaps too much behind the scene automation.

I have a small proof.
I can implement promotion to "DeviceDiscoveryDialog" , in dialog, but I have to type /copy it in - no "pull down" control to help me.
However, "DeviceDiscoveryDialog" has to be valid class.
So the QtDesigner have knowledge about the "DeviceDiscoveryDialog", but it cannot be selected via "standard" pull down control.
Unfortunately is it these (little) "gotcha " which keeps project from smooth development and completion.
But it is fun.