Slots and signals must have same parameters. Otherwise, the connection will not occur. Not only for connection, slot function must have same parameters with signal. For example, this sample doesn’t work: QObject::connect(ui.comboBox, SIGNAL (activated(int)), this, SLOT (onComboboxActivated)); But it works. The connection mechanism uses a vector indexed by signals. But all the slots waste space in the vector and there are usually more slots than signals in an object. So from Qt 4.6, a new internal signal index which only includes the signal index is used. While developing with Qt, you only need to know about the absolute method index.

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• 2Signals
• 3Basic Usage
• 4Example

Overview

Using QPushButton developers can create and handle buttons. This class is easy to use and customize so it is among the most useful classes in Qt. In general the button displays text but an icon can also be displayed.

QPushButton inherits QAbstractButton which in turn inherits QWidget.

Signals

Inherited from QAbstractButton

• void clicked(bool checked = false)
• void pressed()
• void released()
• void toggled(bool checked)

Inherited from QWidget

• void customContextMenuRequested(const QPoint &pos)

Inherited from QObject

• void destroyed(QObject *obj = nullptr)

Basic Usage

Text

The text of QPushButton can be set upon creation or using setText(). To get the current text of the button use text().

Icon

The icon of QPushButton can also be set upon creation. After creation the icon can be changed using setIcon() To get the current icon of the button use icon()

Set Position and Size

To set the position and the size of the button use setGeometry(). If you want just to modify the size of the button use resize()

Handle Button

QPushButton emits signals if an event occurs. To handle the button connect its appropriate signal to a slot:

connect(m_button, &QPushButton::released, this, &MainWindow::handleButton);

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Example

The following simple code snippet shows how to create and use QPushButton. It has been tested on Qt Symbian Simulator.

An instance of QPushButton is created. Signal released() is connected to slot handleButton() which changes the text and the size of the button.

To build and run the example:

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1. Create an empty folder
2. Create a file for each of the below code snippets and add the example code to them (the name of the file should match the name above the snippet).
   • All 4 files must be in the same folder.
3. Using command line, navigate into the folder with the 4 files.
4. run qmake on the project file: qmake PushButtonExample.pro
   • If successful it will not print any output.
   • This should create a file with the name Makefile in the folder.
5. Build the application: make
   • The application should compile without any issues.
6. Run the application: ./PushButtonExample

The above steps are for linux but can easily be followed on other systems by replacing make with the correct make call for the system.

mainwindow.h

mainwindow.cpp

main.cpp

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PushButtonExample.pro

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