QLayout: attempting to add QLayout "" to MainWindow, which already has a layout (solved)

[SGaist]

Hi,

If MainWindow is a QMainWindow and you build centralWidget in MainWindow just call setCentralWidget(centralWidget);

You can't set a layout on a QMainWindow because it already has one that makes all the work for dock widgets etc.

[houmingc]

In mainWindow, i have to transverse between 5 pages using a timer.
QWidget do not have method setCentralWidget();

QWidget* w_page1;
QWidget* w_page2;
QWidget* w_page3;
QWidget* w_page4;
QWidget* w_page5;

  w_page1->setLayout(Layout_page1);
   w_page1->showMaximized();
   w_page1->setStyleSheet("background-color:black");
   w_page2->setLayout(Layout_page2);
   w_page2->showMaximized();
   w_page2->setStyleSheet("background-color:black");

   w_page3->setLayout(Layout_page3);
   w_page3->showMaximized();
   w_page3->setStyleSheet("background-color:white");
   w_page4->setLayout(Layout_page4);
   w_page4->showMaximized();
   w_page4->setStyleSheet("background-color:white");

   w_page5->setLayout(Layout_page5);
   w_page5->showMaximized();
   w_page5->setStyleSheet("background-color:white");

[houmingc]

Layout_page3 = new QHBoxLayout(this);
Layout_page3->addWidget(w);
Layout_page3->addLayout(rightLayout2);
this->setCentralWidget(Layout_page3);

Error
No matching function for call to
MainWindow::setCentralWidget(QHBoxLayout*)

[houmingc]

The code is in github
https://github.com/houmingc/HorizontalLayout1/blob/master/HorizontalLayout/mainwindow.cpp

[SGaist]

setCentralWidget as the name implies needs a QWidget not a QHBoxLayout.
Put your Layout_page3 on a placeholder widget and then set it as central widget

[houmingc]

Layout_page3 = new QHBoxLayout(this);
Layout_page3->addWidget(w);
Layout_page3->addLayout(rightLayout2);
setCentralWidget(Layout_page3);

This doesn't work, neither is this
this->setCentralWidget(Layout_page3);

[SGaist]

Again: setCentralWidget takes a QWidget not a QLayout as a parameter.

Again 2:Put your Layout_page3 layout on a QWidget and then set that widget using setCentralWidget.

QWidget *placeholderWidget = new QWidget;
placeholderWidget->setLayout(Layout_page3);
setCentralWidget(placeholderWidget);

[houmingc]

git push my code. Thanks, although i got no error, but the warning is still there.

[SGaist]

Are you still trying to set a layout on your main window ?

[houmingc]

@SGaist
yes sir

http://picpaste.com/019a8b1d437063802a66d05904e663a6.jpg

[SGaist]

So again: you can not do that as the error message says. As already stated: QMainWindow already has a layout. The one that handles dock widgets, menu bar, status bar etc. You can't replace it. The central content of a QMainWindow is a QWidget, so create one widget that does what you want and set it using setCentralWidget.

[Narasimha Reddy MV]

You are Creating Layout inside a widget so Don't use (Parent Instance) 'this' pointer.

Layout_page3 = new QHBoxLayout;

try this it will work

[Qterry.wang]

Good afternoon every one!
I encour this issue too, Msg is:

18:28:21: Debugging starts
QLayout: Attempting to add QLayout “” to MainWindow “MainWindow”, which already has a layout

Reason:
I used the following In QMainwindow:
====error code=> QGridLayout *t_gridLayout_map = new QGridLayout(this);
Solution:
remove "this" as the following:
====OK code=> QGridLayout *t_gridLayout_map = new QGridLayout();

That's OK!
have a good day!

[JonB]

@Qterry-wang said in QLayout: attempting to add QLayout "" to MainWindow, which already has a layout (solved):

QGridLayout *t_gridLayout_map = new QGridLayout();

This does not address the issue. It merely creates a currently-unparented QGridLayout, it depends what you then do with that. You cannot then add it directly to this, the MainWindow, since that already has a layout.

[Diaxion]

@Qterry-wang wow I was also getting similar warning and i deleted parameter like you, warning was gone. THX !