1. Blanchette and Summerfield, Ch. 2
QT – Dialogs
Blanchette and Summerfield, Ch. 2

2. Overview
About Qt – widgets, signals and slots, synchronization, layout
Windows vs. Qt dialog handling
Example – findDialog
Steps in defining and implementing subclass findDialog (objects and c++ file structure)
Define subclass: finddialog.h
Implement subclass: finddialog.cpp
Execute: main.cpp
More signals and slots
Qt Designer
Learn by doing

3. Hello, Qt!
Quick review of last time
Qt-ese

4. Hello, Qt! A bit for dramatic effect, but there will be advantages
#include <QApplication>
#include <QLabel>
int main(int argc, char *argv[]) {
QApplication app(argc, argv);
QLabel *label = new QLabel("Hello Qt!");
label->show();
return app.exec(); }
A bit for dramatic effect, but there will be advantages
Just a label in a field with no real “main window”
Will look at some basics tonight
Slots and signals (vs. event queues), and layouts (this is a GUI builder),

5. Hello, Qt!
#include <QApplication> // Definitions of QApplication and #include <QLabel> // QLabel classes // Qt is truly object-oriented int main(int argc, char *argv[]) { QApplication app(argc, argv); // Creates a QApplication object to // manage app-wide resources QLabel *label = new QLabel("Hello Qt!"); // Creates a QApplication widget (used as // a window) that displays string label->show(); // Make label (window) visible return app.exec(); // Passes control to Qt } // (would also delete QLabel)

6. Handling Events: Signals and Slots
Qt not handle events (or event queue) directly
Qt widgets emit signals when user action or change of state occurs
Signal can be connected to a function, or slot
When signal emitted the slot, or function, is executed
In example, will connect button’s clicked signal to slot - function quit()
quit() is “built-in” QApplication function (object)

7. A Signal and A Slot
#include <QApplication> // Include class definitions #include <QPushButton> int main(int argc, char *argv[]) { QApplication app(argc, argv); // Create QApplication object QPushButton *button = new QPushButton("Quit"); // Create labeled button // Associate (connect) a particular signal of this application with a slot QObject::connect(button, SIGNAL(clicked()), &app, SLOT(quit())); button->show(); return app.exec(); // Pass control to QT }

8. Synchronization & Layout of 2 Widgets
Creates three widgets:
QSpinbox, QSlider, QWidget (application’s main window, will be parent of others)
Using signals and slots of the QSpinbox and QSlider, set value of one depending on value set in the other
E.g., change spinbox value to 70, slider will move to appropriate position
Change slider to some position, spinbox value will be changed based on position
“Layout manager” object will set size and position of widgets

9. “Setting up”, 1/3
#include <QApplication> // Include class definitions,
#include <QHBoxLayout> // including for layout, slider
#include <QSlider> // and spinbox
#include <QSpinBox>
int main(int argc, char *argv[]) {
QApplication app(argc, argv);
QWidget *window = new QWidget; // Again, window will be widget
window->setWindowTitle("Enter Your Age"); // Not good interface design

10. Create & Synchronize Widgets, 2/3
QSpinBox *spinBox = new QSpinBox; // Create spinbox and slider QSlider *slider = new QSlider(Qt::Horizontal); spinBox->setRange(0, 130); // Set/define range of each slider->setRange(0, 130); // As before, a particular widget signal causes a function (slot) to be called // here, when the value in the spinbox is changed, the function to set the value in the // slider is called, and passed the new value of the spinbox to be the new value of the slider QObject::connect(spinBox, SIGNAL(valueChanged(int)), slider, SLOT(setValue(int))); // … and vice versa QObject::connect(slider, SIGNAL(valueChanged(int)), spinBox, SLOT(setValue(int))); spinBox->setValue(35); // Set initial value for spinbox, slider will then get set

11. Dialogs, and Qt
“Dialog” in ui programming refers to exchange of information of user and program
See Dix et al. and others for thorough treatment
Dialog boxes are ui elements that can do this, as are other elements
For Qt-ese, just say “dialogs”
“GUI applications” consist of main window, menu bar, tool bar, … and many dialog boxes (dialogs)
From a programming perspective, could create an application that was just a “dialog”, e.g., calculator

12. Windows vs. Qt Dialog Handling
Recall, windows api requires:
Creation of form and elements of dialog, or widgets, (resource script or visually – tool - created)
Display of dialog (wndproc – event handling procedure)
Separate dialog function for dialog event handling
Post dialog function handling (in wndproc)
Similarities and differences with Qt
Dialog elements (widgets) created (program or visually - tool)
Display of dialog (by program and widget)
Not separate dialog function – slots and signals for control flow
Different post dialog handling (essentially none, dialog widget)

13. Dialogs –1st Example Implement dialog as (sub)class
Independent, self-contained component
Signals and slots all in one
No “window”
QWidget > QDialog > FindDialog
At right, from last time – QDialog not shown
Dialog consists of 5 widgets
Edit box, 2 check boxes, 2 buttons
Program will do class setups, definition and placement of widgets
Three files:
finddialog.h, finddialog.cpp, main.cpp

14. Steps in Defining and Implementing Subclass findDialog
Will look at the code in detail – “survival kit” for creating dialogs
1. finddialog.h
Set up: include, forward declarations
FindDialog subclass definition
2. finddialog.cpp
Will implement findDialog class:
Create dialog elements (widgets)
Connect signals and slots
Lay out widgets using layout managers
Define slots, or functions
3. main.cpp
As before, create new object, show it, and execute

15. 1. finddialog.h Set up: include, forward declarations
#ifndef FINDDIALOG_H // For c++ preprocessor – only include once #define FINDDIALOG_H #include <QDialog> // QDialog is Qt base class (it inherits Qwidget) // Again, below from last time class QCheckBox; // forward declarations of the Qt classes used class QLabel; // tells C++ compiler exists, later defined class QLineEdit; class QPushButton;

16. finddialog.h FindDialog - Subclass Definition
class FindDialog : public QDialog // FindDialog is a subclass of QDialog { Q_OBJECT // Required macro for classes defining sgnls or slots public: FindDialog (QWidget *parent = 0); // Qt widget class constructor, here, no parent // (“signals” and “slots” are macros) signals: // Define signal emitted when “Find” button clicked void findNext (const QString &str, Qt::CaseSensitivity cs); // depends on match case void findPrevious (const QString &str, Qt::CaseSensitivity cs); // Qt::Ca… is an enum type private slots: // Define slots void findClicked (); void enableFindButton (const QString &text); private: // Forward declarations of classes QLabel *label; QLineEdit *lineEdit; QCheckBox *caseCheckBox; QCheckBox *backwardCheckBox; QPushButton *findButton; QPushButton *closeButton; }

17. 2. finddialog.cpp Implement finddialog class: Create dialog elts (widgets)
#include <QtGui> // Definitions of Qt’s GUI classes - hundreds #include "finddialog.h“ FindDialog::FindDialog (QWidget *parent) : Qdialog (parent) // pass parent to base class constructor { label = new Qlabel (tr ("Find &what")); // Create dialog element, Qlabel, etc lineEdit = new QLineEdit; // tr func for translation, & indicates shortcut key label->setBuddy (lineEdit); // “buddy” is widget that accepts focus w/shortcut caseCheckBox = new QCheckBox (tr ("Match &case")); // Qcheckbox backwardCheckBox = new QCheckBox (tr ("Search &backward")); // Qcheckbox findButton = new QPushButton (tr ("&Find")); // QPushbutton findButton->setDefault (true); // “default” indicates executed on key Enter findButton->setEnabled (false); // not enabled, grayed out closeButton = new QPushButton (tr ("Close"));

18. finddialog.cpp Connect signals and slots
// Signal “textchanged” from lineEdit widget enables button labeled “find” by private slot enableFindButton connect ( lineEdit, SIGNAL (textChanged (const QString &)), this, SLOT (enableFindButton (const QString &))); // Again, private slot, findClicked, called when signal “clicked” emitted by widget findbutton connect ( findButton, SIGNAL (clicked ()), this, SLOT (findClicked ())); // As before, Qt function close called when widget closeButton emits clicked signal connect ( closeButton, SIGNAL (clicked ()), this, SLOT (close ()));

19. finddialog.cpp Lay out widgets using layout managers
Layout managers are Qt’s “system” for positioning display elements, e.g., widgets, spacers
MUCH more flexible than windows
Easily, and naturally, supports incremental development
… and have their own terminology and rules, e.g., nested, boxes
Will work through example

20. finddialog.cpp Lay out widgets using layout managers
// layouts are nested – constrain widgets and other layouts QHBoxLayout *topLeftLayout = new QHBoxLayout; topLeftLayout->addWidget(label); topLeftLayout->addWidget(lineEdit); QVBoxLayout *leftLayout = new QVBoxLayout; leftLayout->addLayout(topLeftLayout); leftLayout->addWidget(caseCheckBox); leftLayout->addWidget(backwardCheckBox);

21. finddialog.cpp Lay out widgets using layout managers
// layouts are nested – constrain widgets and other layouts QHBoxLayout *topLeftLayout = new QHBoxLayout; topLeftLayout->addWidget(label); topLeftLayout->addWidget(lineEdit); QVBoxLayout *leftLayout = new QVBoxLayout; leftLayout->addLayout(topLeftLayout); leftLayout->addWidget(caseCheckBox); leftLayout->addWidget(backwardCheckBox);
QVBoxLayout *rightLayout = new QVBoxLayout;
rightLayout->addWidget(findButton);
rightLayout->addWidget(closeButton);
rightLayout->addStretch(); // fill – here, below

22. finddialog.cpp Lay out widgets using layout managers
// layouts are nested – constrain widgets and other layouts QHBoxLayout *topLeftLayout = new QHBoxLayout; topLeftLayout->addWidget(label); topLeftLayout->addWidget(lineEdit); QVBoxLayout *leftLayout = new QVBoxLayout; leftLayout->addLayout(topLeftLayout); leftLayout->addWidget(caseCheckBox); leftLayout->addWidget(backwardCheckBox);
QVBoxLayout *rightLayout = new QVBoxLayout;
rightLayout->addWidget(findButton);
rightLayout->addWidget(closeButton);
rightLayout->addStretch(); // fill – here, below
QHBoxLayout *mainLayout = new QHBoxLayout;
mainLayout->addLayout(leftLayout);
mainLayout->addLayout(rightLayout);
setLayout(mainLayout);
setWindowTitle (tr ("Find")); setFixedHeight (sizeHint().height()); }

23. FindDialog Constructors - Parent-child Relationships
text

24. Define finddialog slots, or functions
// Called when user clicks Find button, emits signal findPrevious() or findNext
void FindDialog :: findClicked() {
QString text = lineEdit->text();
Qt::CaseSensitivity cs =
caseCheckBox->isChecked() ? Qt::CaseSensitive
: Qt::CaseInsensitive;
if (backwardCheckBox->isChecked()) {
emit findPrevious(text, cs);
} else {
emit findNext(text, cs); // emit keyword (macro) specific to Qt }
// Called whenever user changes text in line editor, enables button if there is text in line editor
void FindDialog :: enableFindButton(const QString &text)
findButton->setEnabled (!text.isEmpty ());

25. 3. main.cpp
// As before, simply create a new object, here FindDialog, show it, and execuute #include <QApplication> #include "finddialog.h“ int main (int argc, char *argv[]) { QApplication app (argc, argv); FindDialog *dialog = new FindDialog; dialog->show(); return app.exec(); }

26. More about Signals and Slots
“Signals and slots enables application programmer to bind objects together without objects knowing anything about each other”
Essentially c++ member functions
Can be virtual, overloaded, public, protected, private, invoked indirectly
Connected to a signal and automatically called each time the signal is emitted
connect (sender, SIGNAL (signal), receiver, SLOT (slot) )
So far, only different signals to different slots
Other ways, as well

27. Signals and Slots Again, form is:
connect (sender, SIGNAL (signal), receiver, SLOT (slot) )
1. One signal can be connected to many slots:
connect(slider, SIGNAL(valueChanged(int)),
spinBox, SLOT(setValue(int)));
this, SLOT(updateStatusBarIndicator(int)));
When signal emitted, slots called one after the other, in arbitrary order
2. Many signals can be connected to the same slot:
connect(lcd, SIGNAL(overflow()),
this, SLOT(handleMathError()));
connect(calculator, SIGNAL(divisionByZero()),
When either signal is emitted, the slot is called.

28. Signals and Slots
connect (sender, SIGNAL (signal), receiver, SLOT (slot) )
3. A signal can be connected to another signal:
connect(lineEdit, SIGNAL(textChanged(const QString &)),
this, SIGNAL(updateRecord(const QString &)));
When the first signal is emitted, the second signal is emitted as well.
4. Connections can be removed:
disconnect(lcd, SIGNAL(overflow()),
this, SLOT(handleMathError()));

29. Can Use Signals not only with Widgets, but as More General Mechanism
// Define class class Employee : public QObject { Q_OBJECT public: Employee() { mySalary = 0; } int salary() const { return mySalary; } public slots: void setSalary (int newSalary); signals: void salaryChanged (int newSalary); private: int mySalary; };
// Use signal to communicate with any/all slots
// (functions) connected to salaryChanged
// signal!
void Employee::setSalary (int newSalary) {
if (newSalary != mySalary) {
mySalary = newSalary;
emit salaryChanged (mySalary); }

30. Qt Designer – Qt’s Visual Tool: Layout, widgets, …x

31. Qt Designer – Qt’s Visual Tool: Layout, widgets, …x

32. Qt Designer .

33. End
… and you’re off and running …