Qt Tutorials For Beginners 9 - How to Show Another Window From MainWindow in QT

In this QT C++ GUI tutorial I will show you How to open a new window from a button. So you will learn to Open new window when button on main-window is clicked. i.e. using QMainWindow open a new QMainWindow, qt open another window, close window qt
transparent window qt, qt create popup window, qt open dialog from mainwindow, qt multiple windows
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DISCLAIMER: This video and description contains affiliate links, which means that if you click on one of the product links, I’ll receive a small commission. This help support the channel and allows us to continue to make videos like this. Thank you for the support!

[@mikkykyluc5804]

Thank you very much! I'm a 1-year programming student and wanted to experiment with making a simple GUI-based text game, this is just what I needed :)

[@RicardoAGLourenco]

My tip of the day ... Help him seeing the ad to the end

[@skyletwings5711]

100% exactly what I was looking for. Thanks a lot!

[@user-ww2lc1yo9c]

As expected, there is a lot of sophistication in creating GUIs, lot of options and widgets to make that easy. I learnt VB6 almost 20 years ago. This seems so much more better than that technology.

[@andrexbsb]

Very good. In this video you say everything I was looking for and was not finding. Thank you very much.

[@MikeSmith-te6cn]

Thanks, I'm new to Qt and wasn't given much time for this aspect of the project and the learning curve involved with any software package like Qt. Videos like yours help tremendously. Good work !

[@thex-man9153]

Hi, please assist me. How can I pass data from the dialog window to the mainwindow? Like to write something on a dialog window and when I press a button it should appear on the main window

[@yashgovindani4234]

You have explained it nicely; but a small request can you also add videos on how create installer for qt applications using Qt Installer Framework (For : Mac, Windows as well as Linux).

[@tobyadams5763]

I'm out of a fix once more...thanks to this video!😀

[@user-ql7pw7ld1n]

Amazing..loved it fully

[@katjaczajkov8694]

i prefer to use some different words, so any people can learn it easy like this exam. S2 = new Sec_Dialog(this); S2->exec(); so u see better that Sec_Dialog must be the class and S2 the object. different words, better readable

[@MoesKeckeEcke]

Keyboard Shortcut used at 7:57 (Un)Comment Selection Press CTRL + /

[@MJ-og8zg]

mac users: command + /

[@BharathRamMS]

Thanks

[@eldukasoooficial5601]

There you use setmodal because the new window you open is QWidget, and if the new window to open was of type QMainWindow, what should I put instead of setmodal?

[@georgymoshkin2079]

Excellent tutorials! While learning this one I got an error "expected type specifier". It was problem with capital letter: secDialog=new SecDialog(this); SecDialog=new secDialog(this); Anyone having the same error pay attention to variable names (small letters or capital letters).

[@malbarenque]

Thank you from Argentina

[@valizeth4073]

Shouldn't you delete the memory for the secDialog* ? I've heard about Qt's reference counting but yet, you call delete ui in the main window destructor?

[@TheFinalCutBG]

There is WAY BIGGER PROBLEM here. Since the constructor of secDialog takes this as argument, it is a child of QMainWindow, when QMainWindow gets destroyed, it will destroy the dialog also... BUT in the example shown in the video on EVERY click, a new Dialog is created, and the pointer to the previous one is lost inevitably, hence a memory leak occurs. The correct way to do it is to create the dialog in the constructor of QMainWindow and assign the button to only show it. Edit: Even if QT tracks the allocations and deletes them later, it's absolutely pointless to create the same thing over and over again... it's just stupid.

[@priyeshgupta164]

@@TheFinalCutBG please respond if you can find the time for the question:: how to create a single 2nd dialogue from push button in mainn window; and keep on showing the same dialogue if the button is clicked again, without creating more instances of 2nd dialogue window.

[@TheFinalCutBG]

@@priyeshgupta164 if you want your second dialog to keep a certain state, make it a member variable (not a pointer) of QMainWindow. That way it lives as long as QMainWindow lives, and when QMainWindow is destroyed, the dialog is automatically destroyed also. The parent argument in the constructor of the second dialog should be nullptr. When the button is clicked, you call second dialog's show() function.

[@chanyanhan7791]

Thanks for that :") It help me a lot and what if I used back button how do I go back ?

[@sachinacharya1032]

I'm developing a Qt application for the nanopc t2. I have a few different screens and as I move forward and back through the different screens, the application gets slower and slower. In the end it gets very slow.

[@just_kidding_kid]

That was helpful, thanks for video

[@niltonrodolforodrigues9093]

Thanks!

[@masintec]

thanks for your sharing !

[@Manas-co8wl]

I checked the docs and exec() always pops the dialog as modal, ignoring the parameter set by setModal method

[@duzantj-laurent7784]

how can i pass data/variables from my mainwindow to an other window (dialog) ? is that possible ? if so you do a tutorial pls

[@paulg.3067]

isn’t signals&slots meant to be used for that ?

[@iordanbaltaliiski2882]

Great video :)

[@digimikeh]

Perfect

[@user-bc8pr5up2r]

very well!

[@maurofoti526]

you forgot to call the delete on secDialog in the destructor

[@Xerox482]

it will generate xxxx.exe have stopped working popup in case you have not opened child windows and directly close the main window.

[@cooldued00755]

how to make the mainwindow show up again once we close the second dialog,

[@rusikarhireev]

In secdialog.ui right click on the main window and "Go to slot" -> "finished(int)". In generated function you just have to call "show" function on the object returned by parentWidget(): void SecondDialog::on_SecDialog_finished(int result) { parentWidget()->show(); }

[@xuelin9983]

in SecondDialog::SecondDialog, add this code ===> connect(this, SIGNAL(finished(int)), this->parentWidget(), SLOT(show()));

[@altankursad]

QObject::connect: No such signal programHazirla::finished(int) in ../YayMakinesi2Eksen/programhazirla.cpp:9 QObject::connect: (sender name: 'programHazirla') QObject::connect: (receiver name: 'MainWindow') programHazirla is my second window... When I click button on second window is hidden but main window is not show again.. How Can i solve that problem?

[@altankursad]

I solved i think. On button click in second window, i add this->parentWidget()->show(); functions. after hide() command.

[@zakariachahboun]

thank you :)

[@rosariodipalma8564]

Nice tutorial. But the secDialog object when it is deallocated?

[@musabse]

nice

[@WHWrooolz]

I don't want to open up a sepparate dialogue window. what I want to do is open up a new view over the main window. I want the user to navigate with pushbuttons to different pages within the mainWindow, without a sepparate modal/non-modal dialogue. So lets say I'm making an educational tool, and my main window shows a title screen along with buttons to navigate from one layout to another, and I want one of those buttons to open up a display with text. I don't want that to generate in a separate window. how would I approach this?

[@RodCDavid]

Don't know if you have found this yet, but you can use the stacked widget.

[@pinniramakrishna2467]

I need to work on multiple windows plz help me. Example I have 3 windows win1, win2 and win3. Win1 has a button that can open win2, win2 has a button that can open win3, win3 has two buttons one is to open win2 another for win1. My problem is how to open(show) win1 from win3. Sorry for any grammatical mistakes.

[@user-ww2lc1yo9c]

When you wrote secDialog = new SecDialog(this); Is it supposed to create a new secDialog window everytime you click it?

[@pheebsbuffayy]

Do you know the answer now

[@geordirendum583]

is it me or you have to add :delete secdialog in the destructor of the main window since we allocated a pointer with ''new''?

[@lopo8000]

how do i show a picture opening a new window like in this video

[@navarajpokharel8980]

I got but how to get back to previous window plz help me in my project 💌

[@Nathaniel-jr3hn]

How do I hide the other form

[@mellahhamida6914]

Hy, i have a problem when i choose add new i don't find "Qt Designer Form Class" i just have "Qt Designer Form" even when I uploaded the same version that you got in the video, Thank u.

[@vigopoli]

Good Morning. I was doing a graphical interface with a lateral menu that according to press one or the other a different ui. The program opens my windows perfectly. And every window the first time I enter works correctly, however the second time I enter, nothing works anymore. I have the suspicion that it is because an object is created ui every time I enter the window. There is some possible solution for this. A greeting and Thanks forward

[@awernek81]

I have two windows. The main one is a Dialog. Both work at the same time. When I go to shut down the system, the Dialog screen does not close.

[@LOCO.AMP00]

how do i connect the window to the menu strip ?

[@lopo8000]

how do i stop sound once secondary window is closed??

[@BAT_24]

sir, can we merge 2 project in a single project???

[@gtacarlito]

How do i access the widgets of Secdialog, for my mainWindow i am able to access them easily by ui->lineedit->append(); , but how do i access the widgets there on secdialog ???

[@oussamasethoum2755]

how can i do to update the ui of the main window ?

[@satadrubera7281]

I am trying to plot in new window. But I am getting two different windows 1: plot window , 2: blank dialog window. How to overcome this ?

[@govindsajgane2301]

How can we show dialogs based on timings

[@roboticsworkshop]

BUG: but in your program for heap memory actually there is a memory leak because u r using "new" keyword and not deleting it anywhere

[@Phatnaru0002]

ATTENTION: To anyone experiencing the error that says that your class has no member named setModal or exec - It's because of the template you chose when creating your class/header/ui - I'm still a noobie myself, so I don't understand WHY this is causing it, but I can tell you that it IS causing it.

[@ShayAxelod22]

Any idea how to fix it?

[@SrQuesoH]

@@ShayAxelod22 they dont have a solution, the error is because only the dialog templates can be called like this. The Main Windows needs to be call with another function. (im sorry if my english is a bit bad x,D)

[@HKGamingPak]

How i can open first window from second using button?

[@devreddy2010]

I did exactly what he said and When i run the code it was poping out a window written hello world on it and when i click on it was closing did anyone had same issue please help where did this hello world came from in window

[@mritunjaysingh6684]

how do I make the first window unresponsive while opening the second window?

[@ercody_t]

this->hide()

[@dlugi196d]

And hide method dosn't hide but close first window, yes or not?

[@vizionthing]

not.

[@ryannguyen2170]

Is there a way to do it without the code?

[@vizionthing]

You need to overcome your programmerphobia

[@kishorechandaralapati4991]

what is the use of .hpp files

[@arteqppp6223]

.h - C | .hpp - C++ (both are working for C++)

[@dontlike1000]

I don't understand why we create second window on a button click. I think it is more obvious to create a pointer to second window right after we create main window. By clicking the button each time we create a new instance of second window in heap. We can create a window one time and then just close and reopen it.

[@contificate]

In your second dialog's constructor, setAttribute(Qt::WA_DeleteOnClose); This will tell Qt's MOC to delete it for you despite being on the heap. You never have to call delete on it. Qt's MOC can be quite.. devious. So a lot of Qt code that looks like it produces leaks won't.

[@artteaparty]

When I code the void MainWindow::on_pushButton_clicked() { SecondDialog secDi; secDi.setModal(true); secDi.exec(); } and build the program, I get no errors but the run button is not green and available :/ Why can't I run it?

[@ninanikdodo]

I am the same!

[@arshsaluja8237]

Did u got the why?

[@dlugi196d]

Hi, but this method: secDialog = new SecDialog(this); secDialog->show(); dose not blocking to open second window again and again, we can open more then one this second window like duplicate. Any advice?

[@MaKetBLUE]

my advice would be to add "secDialog = nullptr;" in the MainWindow constructor, and only allow creating new window when secDialog = nullptr (using an if statement).

[@fab0527]

This is useless. I don't want a new dialog, I want a new mainwindow since I need a menu bar

[@user-mc6sm1ut3t]

.setModal() and .exec() are giving me errors- ‘class SecDialogue’ has no member named 'setModal' and ‘exec’ 22 | secD.exec(); | ^~~~