Qt add buttons to existing widget - qt

Question

I have added two pushButtons using qtDesigner, those buttons are chilldren of centralWidget, now I would like to add one more pushButton, but programmatically in mainwindow.cpp.
When I use setCentralWidget method it removes or hides prevous 2 pushButtons which were added by qtDesigner. My question is how to add this additional button programmatically so those 2 pushButtons remains?
I am beginner in Qt.

Answer 1

The central widget default layout is called gridLayout and is a QGridLayout. You can add the new button to it like this:
ui->gridLayout->addWidget(new QPushButton("Button Text"), rowNumber, colNumber);
Here is an example:
mainwindow.h:
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
class QPushButton;
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
private:
Ui::MainWindow *ui;
QPushButton *newButton;
};
#endif // MAINWINDOW_H
mainwindow.cpp:
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QPushButton>
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow),
newButton(new QPushButton("Button 3"))
{
ui->setupUi(this);
const int rowNumber = 1;
const int colNumber = 0;
ui->gridLayout->addWidget(newButton, rowNumber, colNumber);
}
MainWindow::~MainWindow()
{
delete ui;
}
mainwindow.ui:
<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
<class>MainWindow</class>
<widget class="QMainWindow" name="MainWindow">
<property name="geometry">
<rect>
<x>0</x>
<y>0</y>
<width>400</width>
<height>300</height>
</rect>
</property>
<property name="windowTitle">
<string>MainWindow</string>
</property>
<widget class="QWidget" name="centralWidget">
<layout class="QGridLayout" name="gridLayout">
<item row="0" column="0">
<widget class="QPushButton" name="pushButton1">
<property name="text">
<string>Button 1</string>
</property>
</widget>
</item>
<item row="0" column="1">
<widget class="QPushButton" name="pushButton2">
<property name="text">
<string>Button 2</string>
</property>
</widget>
</item>
</layout>
</widget>
<widget class="QMenuBar" name="menuBar">
<property name="geometry">
<rect>
<x>0</x>
<y>0</y>
<width>400</width>
<height>21</height>
</rect>
</property>
</widget>
<widget class="QToolBar" name="mainToolBar">
<attribute name="toolBarArea">
<enum>TopToolBarArea</enum>
</attribute>
<attribute name="toolBarBreak">
<bool>false</bool>
</attribute>
</widget>
<widget class="QStatusBar" name="statusBar"/>
</widget>
<layoutdefault spacing="6" margin="11"/>
<resources/>
<connections/>
</ui>
Good luck!

Answer 2

You can add QPushbutton to central widget by passing its object name.
QPushButton *PB=new QPushButton(ui->centralwidgetobjectname);
PB.show();
Otherwise create layout inside Central widget then using addwidget function to add Qpushbutton.
QGridLayout *GL=new QGridLayout(this);
QPushButton *PB=new QPushButton();
GL->addWidget(PB);
Set Geometry For Grid Layout.