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.