Child Layouts not getting added Properly

[Adit]

I'm new to qt and exploring it .Basically Im adding three child layouts to a Parent layout.But after having added the third layout,my first layout disappears. This is my code:

MainWindow::MainWindow(QWidget *parent) :
QWidget(parent),
ui(new Ui::MainWindow)
{

this->setGeometry(500,650,1000,1000);

QVBoxLayout *parentLayout = new QVBoxLayout(this);

QVBoxLayout *l1 = new QVBoxLayout();
QWidget *lw1 = new QWidget;
lw1->setMaximumHeight(50);
lw1->setStyleSheet("background-color:brown");
l1->addWidget(lw1);

QHBoxLayout *l2 = new QHBoxLayout;

QLabel *label = new QLabel("Industry");
label->setStyleSheet("color:white");
label->setMaximumWidth(300);
l2->addWidget(label);

QComboBox *cb = new QComboBox;
cb->addItem("Movie");
cb->setStyleSheet("background-color:white");
cb->setMaximumHeight(50);
l2->addWidget(cb);

parentLayout->addLayout(l1);
parentLayout->addLayout(l2);

//If I run till here I see the added two child layouts.

QWidget *w3 = new QWidget;
w3->setStyleSheet("background-color:white");

QVBoxLayout *l3 = new QVBoxLayout();
l3->addWidget(w3);

//parentLayout->addLayout(l3);
//If I uncomment the above line then I see only layouts l2 and l3 from the top and not l1

}

Basically what I need is a Layout which in turn containing multiple subLayouts of varied sizes.Could someone highlight me where am I doing mistake.Any help will be really useful.

[J.Hilk]

hi,

I assume this is the default MainWindow from QtCreator ProjectWizard.

in that case, this already has a layout and you can not simply assign a new one

change this

@Adit said in Child Layouts not getting added Properly:

QVBoxLayout *parentLayout = new QVBoxLayout(this);

to

QVBoxLayout *parentLayout = new QVBoxLayout(ui->centralWidget);

[JonB]

Following on from @J-Hilk's doubtless-correct analysis:

@Adit

QVBoxLayout *parentLayout = new QVBoxLayout(this);

If you ran this from a debugger, did you not get a warning message saying "warning adding a layout to ... which already has an existing layout"?

@J-Hilk

QVBoxLayout *parentLayout = new QVBoxLayout(ui->centralWidget);

Is this the same as

QVBoxLayout *parentLayout = new QVBoxLayout();
ui->centralWidget->setLayout(parentLayout);

?

[J.Hilk]

@JonB said in Child Layouts not getting added Properly:

@J-Hilk

QVBoxLayout *parentLayout = new QVBoxLayout(ui->centralWidget);

Is this the same as
QVBoxLayout *parentLayout = new QVBoxLayout();
ui->centralWidget.seLayout(parentLayout);

?

yes, with the setLayout call, the Layout gets reparented to centralWidget.

[Adit]

Guys , here my MainWindow is not a QMainWindow,instead ,it inherits from QWidget.Moreover I dont use the .ui form and I create the UI dynamically.

[J.Hilk]

@Adit
what's the ui-pointer for than?

MainWindow::MainWindow(QWidget *parent) :
QWidget(parent),
ui(new Ui::MainWindow)
{

[Adit]

Sorry @J-Hilk ,but Im not using it .I tried to add both setMinimumHeight and setMaximumHeight and it works now.Could you tell me when these two functions should be used?

[jsulm]

@Adit What about http://doc.qt.io/qt-5/qwidget.html#setLayout ?
You created a layout (parentLayout), but you did not tell your MainWindow widget to use it.

[Adit]

But I have set the MainWindow widget as parent to the Top-Layout created and it works!

[J.Hilk]

@Adit
It gets a bit tricky when you add Layouts to Layouts.

it should also work, if you specify strechfactors for the addes layouts e.g

parentLayout->setStretch(0,1);
parentLayout->setStretch(1,1);
parentLayout->setStretch(2,1);

[Adit]

I guess stretch factors can be 0 or 1 (contract and expand) right?What if we have multiple Layouts of specific sizes ?

[J.Hilk]

@Adit said in Child Layouts not getting added Properly:

I guess stretch factors can be 0 or 1 (contract and expand) right?What if we have multiple Layouts of specific sizes ?

no, 0 means, take as much space, as possible, defined by the sizepolicy and sizehint of the Widget/Layout

in this case a stretch factor of 1 for each element results in the following space for the layouts, 1/3, 1/3 and 1/3.

With for example

parentLayout->setStretch(0,1);
parentLayout->setStretch(1,1);
parentLayout->setStretch(2,2);

the layouts take up 1/4, 1/4, 1/2 of the available space.

[Adit]

If we are using this setStretch() method, then can we use setMaximumWidth() and setMaximumHeight() methods?

[J.Hilk]

@Adit yes, the stretch is applied until min and max sizes are hit and as long as no contradicting QSizePolizies are set (like fixed size)

[Adit]

Could you suggest me some idea to build a complex layout(i.e sublayouts of varying sizes)?Could you suggest me an opensource project for building a resolution independent UI.