Signals and slots are used for communication between objects. The signals and slots mechanism is a central feature of Qt and probably the part that differs most from the features provided by other frameworks. The minimal example requires a class with one signal, one slot and one connection: counter.h. I have been looking at the above example and searching for more recent examples but I just cannot get my code to work. Can anyone point me in the direction of an example or see what is wrong with the code below? As I say, I am using Qt5 @ import QtQuick 2.0. Rectangle id: guide width: 800 height: 600 signal qmlSignal(string msg).

last modified November 30, 2020

In this part of the Qt5 C++ programming tutorial, we create our first programs.

We display a tooltip and various mouse cursors. We center a window on the screenand introduce the signal and slot mechanism.

Simple example

We start with a very simple example.

The example shows a basic window on the screen.

We include necessary header files.

This is the application object. Each Qt5 application must create this object.(Except for console applications.)

This is our main widget.

Here we resize the widget and set a title for our main window. In this case,the QWidget is our main window. And finally, we showthe widget on the screen.

The exec method stars the main loop of the application.

A tooltip

A tooltip is a specific hint about an item in an application. Thefollowing example will demonstrate, how we cancreate a tooltip in Qt5 programming library.

The example shows a tooltip for the main QWidget.

We set a tooltip for the QWidget widget with thesetToolTip method.

Qt5 Cursors

A cursor is a small icon that indicates the position of the mouse pointer. Inthe next example will show various cursors that we can use in our programs.

In this example, we use three frames. Each of theframes has a different cursor set.

A QFrame widget is created.

We set a frame style with the setFrameStyle method. This way we cansee the boundaries of the frames.

A cursor is set to the frame with the setCursor method.

This will group all the frames into one row. We will talk more about this in thelayout management chapter.

Qt5 QPushButton

In the next code example, we display a push button on the window.By clicking on the button we close the application.

In this code example, we use the concept of the signalsand slots for the first time.

We create a new QPushButton. We manually resize it and place iton the window with the setGeometry method.

When we click on the button, a clicked signal is generated. A slotis the method which reacts to the signal. In our case it is the quit slot of the main application object. The qApp is a global pointerto the application object. It is defined in the QApplication headerfile.

Plus minus

We finish this section showing how widgets can communicate. The code is splitinto three files.

This is the header file of the example. In this file, we define twoslots and a label widget.

The Q_OBJECT macro must be included in classes thatdeclare their own signals and slots.

We have two push buttons and a label widget. We increase or decreasethe number displayed by the label with the buttons.

Here we connect the clicked signals to their slots.

In the OnPlus method, we determine the current value of the label.The label widget displays a string value, so we must convert it to the integer.We increase the number and set a new text for the label. We convert a number tothe string value.

Qt Signal Slot Example C

This is the main file of the code example.

Qt Signal Slot Example

In this chapter, we created our first programs in Qt5.