L1-L4 Lab.pdf

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Qt in Education

Lab 1 – The Basics of Qt

Aim:

This lab will take you through all the steps required to

build a fully fledged Qt application. The focus is to

understand how a Qt application is structured and to

learn to find your way round the Qt documentation.

Duration:

Qt in Education

Goals and Background

The goal of this lab is to apply the knowledge from the first lectures and put it in a

context. The task at hand is to develop a fully fledged desktop application – a text

editor with support for multiple documents, saving and loading, undoing, the

clipboard, etc.

Throughout this lab, new features will be added to the application gradually. The

purpose of this is twofold. First, this is how real world software is developed. The

feature set grows over time. Secondly, you will have a working application from the

very first step so that you can test, verify and debug the functionality continuously.

Do not keep a known bug to a later step, make sure that the application works at all

times. It will only be harder to properly troubleshoot in a more complex application.

In the lab, the instructions will be less detailed than in the exercises. This means that

you are expected to look up classes in the Qt reference documentation, and that

adding header files and other trivial code is up to you.

Qt in Education

The Basic Application

The basic application is built from the

Qt4 Gui Application

template. Create such a

project and include the

QtCore

and

QtGui

modules. Base the skeleton on the

QMainWindow

class. In this lab, the project is called

TextEditor.

The resulting project consists of the following files:

•

TextEditor.pro

mainwindow.ui

– the project definition file.

– the implementation and declaration of the

class.

– the user interface for the

MainWindow

class.

MainWindow

mainwindow.cpp

main.cpp

– the

main

function. Gets everything initialized and started.

Review these files and verify that the project builds and runs.

Adding User Interface Elements

The next step is to add a

QTextEdit

widget and the basic user operations

New, Close

and

Exit

to the main window.

First of all, we need to add an icon resource to the project in question. This is

because the icons will be used in the user interface which you are about to design.

Add a new Qt Resource file to the project. Name it

icons.qrc.

Open the resulting file,

add the prefix

icons

and add the

*.png

files for this lab.

Now you are ready to start working on the user interface. Start by opening the

mainwindow.ui

file in Designer mode.

Qt in Education

Add a

QTextEdit

widget to the main window and lay it out. Select the window itself to

alter the margins of the layout to zero to get the new widget to fill the central area

fully.

When the widget is in place you can try the dialog using

Tools

–

Form Editor

–

Preview

(Ctrl+Alt+R).

The user operations are represented by

through the

Action Editor

shown below.

QAction

objects. These are administered

Create the following actions.

Text

New

Exit

Name

actionNew

actionClose

actionExit

Icon

Shortcut

Ctrl+N

Ctrl+W

ToolTip

Create a new document

Close current window

Exit application

actionNew

Actions are added to the user interface through drag and drop. Drag the

action onto the toolbar.

Add the entry

File

to the menu bar. Click on the

type here

text and enter

File.

Now

drag and drop the

actionNew

actionClose

and

actionExit

to the menu. Add separators

between each item by dragging the separator into position (you find it on the menu

you are editing).

If you enter “

&File

” as the title of the menu you get a shortcut, “File”,

automatically. To get an ampersand in a menu text, enter “

”.

Qt in Education

Implementing Functionality

Each of the actions added need to be implemented. You do this by right clicking on

the action in question to bring up its context menu. From the menu, pick the

Go to

slot

option and pick the

triggered()

signal from the list that pops up.

Start by implementing the

actionNew

, this brings you to the following source code.

void MainWindow::on_actionNew_triggered()

{

}

In this slot, create a new

MainWindow

object on the heap and show it.

The other two actions,

actionClose

and

actionExit

, already have matching slots

implemented by Qt. Make the following connections in the

MainWindow

constructor,

after the

setupUi

call.

Source

actionClose

actionExit

Signal

triggered()

Destination

this

qApp

Slot

close()

closeAllWindows()

(current window)

(current

application)

Also, make sure to call

setAttribute

and set the

Qt::WA_DeleteOnClose

attribute in the

MainWindow

constructor.

Self Check

•

Ensure that you can open new windows.

Ensure that

File

–

closes the current window.

Ensure that

File

–

Exit

closes all windows and thus terminates the application.

Explain why the

Qt::WA_DeleteOnClose

attribute is set. Where does it come into

play and why is that important?

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