qt designer widgets - ade malsasa akbar · module: intro to qt developing a hello world application...

Qt Designer WidgetsQt Essentials - Training Course

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Produced by Nokia, Qt Development Frameworks

Material based on Qt 4.7, created on March 16, 2011

http://www.ics.com/learning/training/

Part 1

Intro to Qt

Objects in Qt

2/96

Module: Intro to QtDeveloping a Hello World ApplicationHello World using Qt Creator

Intro to Qt 3/96

Module: Intro to Qt

Developing a Hello World ApplicationHello World using Qt Creator

Intro to Qt Developing a Hello World Application 4/96

“Hello World” in Qt

// main.cpp

#include <QtGui>

int main(int argc, char *argv[]){QApplication app(argc, argv);QPushButton button("Hello world");button.show();return app.exec();

}

• Program consists of• main.cpp - application code• helloworld.pro - project file

Demo fundamentals/ex-helloworld


Project File - helloworld.pro

• helloworld.pro file• lists source and header files• provides project configuration

# File: helloworld.proSOURCES = main.cppHEADERS += # No headers used

• Assignment to variables• Possible operators =, +=, -=

See qmake tutorial Documentation


http://qt.nokia.com/doc/latest/qmake-tutorial.html

Using qmake

• qmake tool• Creates cross-platform make-files

• Build project using qmakecd helloworldqmake helloworld.pro # creates Makefilemake # compiles and links application./helloworld # executes application

• Tip: qmake -project• Creates default project file based on directory content

See qmake Manual Documentation

Qt Creator does it all for you


http://qt.nokia.com/doc/latest/qmake-manual.html

Module: Intro to Qt

Developing a Hello World ApplicationHello World using Qt Creator

Intro to Qt Hello World using Qt Creator 8/96

QtCreator IDE

• Advanced C++ code editor• Integrated GUI layout and forms designer• Project and build management tools• Integrated, context-sensitive help system• Visual debugger• Rapid code navigation tools• Supports

multipleplatforms


Overview of Qt Creator Components

See Creator Quick Tour Documentation


http://doc.qt.nokia.com/qtcreator/creator-quick-tour.html

Finding Code -Locator

• Click on Locator or press Ctrl+K (Mac OS X: Cmd+K)• Type in the file name• Press Return

Locator Prefixes• : <class name> - Go to a symbol definition• l <line number> - Go to a line in the current document• ? <help topic> - Go to a help topic• o <open document> - Go to an opened document

See Navigating Around Your Code with Locator Documentation


http://doc.qt.nokia.com/qtcreator/creator-navigation.html

Debugging an Application

• Debug −> Start Debugging (or F5)

See Qt Creator and Debugging Documentation


http://doc.qt.nokia.com/qtcreator/creator-debugging.html

Qt Creator Demo "Hello World"

What we’ll show:• Creation

of an empty Qt project• Adding themain.cpp source file

• Writing of theQt Hello World Code• Showing Locator Features

• Running the application• Debugging

the application• Looking up the text property of our button

• There is more to Qt CreatorSee Qt Creator Manual Documentation


http://doc.qt.nokia.com/qtcreator/index.html

Module: Objects in QtCommon Features of Qt’s Object ModelObject Communication using Signals & SlotsSignal/Slot VariationsHandling Events in Qt

Objects in Qt 14/96

Module Learning Objectives

• Learn ...• ... about Qt’s object model• ... about parent-child relationships in Qt• ... what a widget is• ... how to combine widgets• ... what signals & slots are• ... how to use signals & slots for object communication• ... which variations for signal/slot connections exist• ... how to create custom signals & slots• ... how Qt handles events

Objects in Qt 15/96

Module: Objects in Qt

Common Features of Qt’s Object ModelObject Communication using Signals & SlotsSignal/Slot VariationsHandling Events in Qt

Objects in Qt Common Features of Qt’s Object Model 16/96

Qt’s C++ Object Model - QObject

• QObject is the heart of Qt’s object model• Adds features to C++, like ...

• Signals and slots• Properties• Event handling• Memory management• ...

• Some features are standard C++• Some use Qt’s meta-object system

• QObject has no visual representation


Object Tree

• QObjects organize themselves in object trees• Based on parent-child relationship

QObject

QObject

QObject

Children

Parent• QObject(QObject *parent = 0)• Parent adds object to list of children• Parent owns children

• Construction/Destruction• Tree can be constructured in any order• Tree can be destroyed in any order

• if object has parent: object first removed from parent• if object has children: deletes each child first• No object is deleted twice

Note: Parent-child relationship is NOT inheritance


Creating Objects

• On Heap - QObject with parent:QLabel *label = new QLabel("Some Text", parent);

• QLayout::addWidget() and QWidget::setLayout() reparentchildren automatically

• On Stack - QObject without parent:• QFile, usually local to a function• QApplication (local to main())• Top level QWidgets: QMainWindow

• On Stack - "value" types See QVariant::Type Documentation

QString name;QStringList list;QColor color;

• Do not inherit QObject• Passed by value everywhere• Exception: QString is implicitly shared (COW strategy)

• Stack or Heap - QDialog - depending on lifetime


http://qt.nokia.com/doc/latest/qvariant.html#Type-enum

Qt’s Widget Model - QWidget

QLabel

QFile

QPushButton

QTextEdit

QWidget

QObject• Derived from QObject• Adds visual representation

• Base of user interface objects• Receives events

• e.g. mouse, keyboard events• Paints itself on screen

• Using styles


Object Tree and QWidget

• new QWidget(0)• Widget with no parent = "window"

• QWidget’s children• Positioned in parent’s coordinate system• Clipped by parent’s boundaries

• QWidget parent• Propagates state changes

• hides/shows children when it is hidden/shown itself• enables/disables children when it is enabled/disabled itself

• Tristate mechanism• For hide/show and enable/disable, ensures that e.g. an explicitly

hidden child is not shown when the parent is shown.• Demo objects/ex-showhide


Widgets that contain other widgets

• Container Widget• Aggregates other child-widgets

• Use layouts for aggregation• In this example: QHBoxLayout andQVBoxLayout

• Note: Layouts are not widgets• Layout Process

• Add widgets to layout• Layouts may be nested• Set layout on container widget


Example Container Widget

// container (window) widget creationQWidget container; // top-level widget on stackQLabel* label = new QLabel("Note:", &container);QTextEdit* edit = new QTextEdit(&container);QPushButton* clear = new QPushButton("Clear", &container);QPushButton* save = new QPushButton("Save", &container);

// widget layoutQVBoxLayout* outer = new QVBoxLayout();outer->addWidget(label);outer->addWidget(edit);QHBoxLayout* inner = new QHBoxLayout();inner->addWidget(clear);inner->addWidget(save);

container.setLayout(outer);outer->addLayout(inner); // nesting layouts

Demo objects/ex-simplelayout


Questions And Answers

• What is an object tree?• Which pointers to QObjects do you need to keep around?• What does it mean when a QWidget has no parent?• Allocate on heap or stack?QWidget; QStringList; QApplication; QString;QFile

• Name some layout managers and when to use them• What does it mean to nest layouts?


Lab: Your first Qt Application

• Implement the application shown here• Search the widgets

• See Qt Widget Gallery Documentation

• ... and choose your os style• Layouts: QHBoxLayout, QVBoxLayout

• See previous slides how to use them• Optionally

• Provide a window title• Add Edit, Remove buttons

• On the right of list• Use group box to provide list caption

Lab objects/lab-firstapp


http://qt.nokia.com/doc/latest/gallery-windowsvista.html



Objects in Qt Object Communication using Signals & Slots 26/96

Callbacks

General ProblemHow do you get from "the user clicks a button" to your businesslogic?

• Possible solutions• Callbacks

• Based on function pointers• Not type-safe

• Observer Pattern (Listener)• Based on interface classes• Needs listener registraction• Many interface classes

• Qt uses• Signals and slots for high-level (semantic) callbacks• Virtual methods for low-level (syntactic) events.


Signals & Slots

• Object Communication• Signal - emitted to notify other objects• Slot - method called in response to signal

• Provides type-safe callbacks• After getting used to it, they are

• easier to use than message maps,• more secure than callbacks,• more flexible than virtual methods

• Fosters component-based programming


Connecting Signals to Slots



Signal emitted

4242



Slot implemented

4242



Signal/Slot connection

4242 4242



4242 4242

QObject::connect( slider, SIGNAL( valueChanged( int ) ), spinbox, SLOT( setValue( int ) ) );



4242 4242

void QSlider::mousePressEvent(...){ ... emit valueChanged( newValue ); ...}



4242 4242

void QSlider::setValue( int value ){ ... m_value = value; ...}



Signal emitted Slot implemented

Signal/Slot connection

4242 4242

void QSlider::mousePressEvent(...){ ... emit valueChanged( newValue ); ...}

void QSlider::setValue( int value ){ ... m_value = value; ...}

QObject::connect( slider, SIGNAL( valueChanged( int ) ), spinbox, SLOT( setValue( int ) ) );

Demo objects/ex-connect


Custom Slots• File: myclass.h

class MyClass : public QObject{Q_OBJECT // marker for moc// ...

public slots:void setValue(int value); // a custom slot

};

• File: myclass.cppvoid MyClass::setValue(int value) {// slot implementation

}


Example of Custom Slots

• QTimer is a class for executing functions at a later time.• Connect the QTimer’s signal timeout() to a custom slot.• Call setSingleShot() for a single-shot timer.• Finally, call start(int msec) on the timer to start it.• For a one-time non-cancellable single-shot timer:QTimer::singleShot(1000, this, SLOT(doit()))

Demo objects/ex-stop-watch


Custom Signals

• File: myclass.hclass MyClass : public QObject{Q_OBJECT // marker for moc// ...

signals:void valueChanged(int value); // a custom signal

};

• File: myclass.cpp// No implementation for a signal

• Sending a signalemit valueChanged(value);

Demo objects/ex-quotebutton


Q_OBJECT - flag for MOC

• Q_OBJECT• Enhances QObject with meta-object information• Required for Signals & Slots• moc creates meta-object information

moc -o moc_myclass.cpp myclass.hc++ -c myclass.cpp; c++ -c moc_myclass.cppc++ -o myapp moc_myclass.o myclass.o

• qmake takes care of moc files for you• Analyze definition of

• Q_OBJECT• signals and slots• emit• At $QTDIR/src/corelib/kernel/qobjectdefs.h

• Look at moc generated files• Demo objects/ex-signalslots


Back to the Original Problem

We asked some slides ago...How to react to a button being clicked?

• Solution:• Implement a slot in your widget• Connect the button’s clicked signal to the slot

• Connect statementconnect(sender, signal, receiver, slot);

• Exampleconnect(button, SIGNAL(clicked()), this, SLOT(onClicked()));


Lab: Connect to Click

• Create an application as shown here• Clicking on “Select Color”

updates label with color’s name.• Hints

• QColorDialog::getColor() to fetch a color• QColor::name() to get the color name

• Optional• In QColorDialog, honor the user clicking “cancel”, and provide it

with the current color to start from.• Set the selected color as the label’s background (Hint: seeQPalette)

Lab objects/lab-selectcolor




Objects in Qt Signal/Slot Variations 36/96

Variations of Signal/Slot Connections

Signal(s) Connect to Slot(s)one

√many

many√

oneone

√another signal

• Signal to Signal connectionconnect(bt, SIGNAL(clicked()), this, SIGNAL(okSignal()));

• Not allowed to name parametersconnect( m_slider, SIGNAL( valueChanged( int value ) )

this, SLOT( setValue( int newValue ) ) )


Making the Connection

Rule for Signal/Slot ConnectionCan ignore arguments, but not create values from nothing

Signal Slot

rangeChanged(int,int)

√setRange(int,int)√setValue(int)√updateUi()

valueChanged(int)

√setValue(int)√updateUi()

X setRange(int,int)X setValue(float)

textChanged(QString) X setValue(int)

clicked()√

updateUi()X setValue(int)



• How do you connect a signal to a slot?• How would you implement a slot?• Name some possible signal/slot connection combinations?• How would you emit a signal?• Do you need a class to implement a slot?• Can you return a value from a slot?• When do you need to run qmake?• Where do you place the Q_OBJECT macro and when do you

need it?


Lab: Source Compatibility

• Implement custom slider• API compatible with QSlider• Shows current value of slider

• To create custom slider• use QSlider and QLabel

• To test slider• main.cpp provides test code• QLCDNumber is part of test code

• Optional:• Discuss pros and cons of inheriting from QSlider instead of

using an instance in a layout.

Lab objects/lab-slider




Objects in Qt Handling Events in Qt 41/96

Event Processing

Qt is an event-driven UI toolkitQApplication::exec() runs the event loop

1 Generate Events• by input devices: keyboard, mouse, etc.• by Qt itself (e.g. timers)

2 Queue Events• by event loop

3 Dispatch Events• by QApplication to receiver: QObject

• Key events sent to widget with focus• Mouse events sent to widget under cursor

4 Handle Events• by QObject event handler methods


Event Handling

• QObject::event(QEvent *event)• Handles all events for this object

• Specialized event handlers• QWidget::mousePressEvent() for mouse clicks• QWidget::keyPressEvent() for key presses

• Accepting an Event• event->accept() / event->ignore()

• Accepts or ignores the event• Accepted is the default.

• Event propagation• Happens if event is ignored• Might be propagated to parent widget

Demo objects/ex-allevents


Example of Event Handling

• QCloseEvent delivered to top level widgets (windows)• Accepting event allows window to close• Ignoring event keeps window open

void MyWidget::closeEvent(QCloseEvent *event) {if (maybeSave()) {writeSettings();event->accept(); // close window

} else {event->ignore(); // keep window

}}

Demo objects/ex-closeevent


Events and Signals

Signals and slots are used instead of events:

• To communicate between components.• In cases where there is a well-defined sender and receiver.

• For example: a button and a slot to handle clicks.• For some events, there is no sender in Qt.

• For example: redraw, keyboard and mouse events.

• To describe high level logic and control flow.

Developers can create custom events if they need to.


Part 2

Widgets

46/96


Qt Designer

Qt Designer 47/96

Qt Designer

• Design UI forms visually

• Visual Editor for• Signal/slot connections• Actions• Tab handling• Buddy widgets• Widget properties• Integration of custom widgets• Resource files

Qt Designer 48/96

Designer Views

Object InspectorDisplays hierarchy of objects on form

Widget BoxProvides selection of widgets, layouts

Property EditorDisplays properties of selected object

Qt Designer 49/96

Designer’s Editing Modes

• Widget Editing• Change appearance of form• Add layouts• Edit properties of widgets

• Signal and Slots Editing• Connect widgets together with signals & slots

• Buddy Editing• Assign buddy widgets to label• Buddy widgets help keyboard focus handling correctly

• Tab Order Editing• Set order for widgets to receive the keyboard focus

Qt Designer 50/96

Designer UI Form Files

• Form stored in .ui file• format is XML

• uic tool generates code• From myform.ui

• to ui_myform.h

// ui_mainwindow.hclass Ui_MainWindow {public:QLineEdit *fileName;... // simplified codevoid setupUi(QWidget *) { /* setup widgets */ }

};

• Form ui file in project (.pro)• FORMS += mainwindow.ui

Qt Designer 51/96

From .ui to C++

OrderForm.uisaves to

designer(Design Mode from Creator) uic

ui_orderform.horderform.h

orderform.cppclass Ui_OrderForm { public: QVBoxLayout *verticalLayout; QLineEdit *lineEdit; QDoubleSpinBox *doubleSpinBox; QSpinBox *spinBox; [...]#include "orderform.h"

#include "ui_orderform.h"

OrderForm::OrderForm(QWidget *parent) : QWidget(parent), ui(new Ui::OrderForm) { ui->setupUi(this);}

OrderForm::~OrderForm() { delete ui; }

produces

Qt Designer 52/96

Qt Creator - Form Wizards• Add New... "Designer Form"

• or "Designer Form Class" (for C++ integration)

Qt Designer 53/96

Naming Widgets

1 Place widgets on form2 Edit objectName property

• objectName defines member name in generated code

Qt Designer 54/96

Form layout in Designer

• QFormLayout: Suitable for most input forms

Qt Designer 55/96

Top-Level Layout

1 First layout child widgets2 Finally select empty space and set top-level layout

Qt Designer 56/96

Preview Widget in Preview Mode

• Check that widget is nicely resizable

Qt Designer 57/96

Code Integration - Header File

// orderform.hclass Ui_OrderForm;

class OrderForm : public QDialog {private:

Ui_OrderForm *ui; // pointer to UI object};

• "Your Widget" derives from appropriate base class• *ui member encapsulate UI class

• Makes header independent of designer generated code

Qt Designer 58/96

Code Integration - Implementation File// orderform.cpp#include "ui_orderform.h"

OrderForm::OrderForm(QWidget *parent): QDialog(parent), ui(new Ui_OrderForm) {ui->setupUi(this);

}

OrderForm::~OrderForm() {delete ui; ui=0;

}

• Default behavior in Qt Creator

Qt Designer 59/96

Signals and Slots in Designer

• Widgets are available as public members• ui->fileName->setText("image.png")

• Name based on widgets object name• You can set up signals & slots traditionally...

• connect(ui->okButton, SIGNAL(clicked()), ...

• Auto-connection facility for custom slots• Automatically connect signals to slots in your code

• Based on object name and signal• void on_objectName_signal(parameters);

• Example: on_okButton_clicked() slot• See Automatic Connections Documentation

• Qt Creator: right-click on widget and "Go To Slot"• Generates a slot using auto-connected name

Qt Designer 60/96

http://qt.nokia.com/doc/latest/designer-using-a-ui-file.html#automatic-connections

Using Custom Widgets in Designer

Choices for Custom Widgets1 Promote to Custom Widget

• Choose the widget closest• From context menu choose

Promote to Custom Widget• Code generated will now refer to given class name

2 Implement a Designer plug-in• Demo $QTDIR/examples/designer/customwidgetplugin

• See Creating Custom Widgets for Qt Designer Documentation

Qt Designer 61/96

http://qt.nokia.com/doc/latest/designer-creating-custom-widgets.html

Dynamically loading .ui files

• Forms can be processed at runtime• Produces dynamically generated user interfaces

• Disadvantages• Slower, harder to maintain• Risk: .ui file not available at runtimeSee Run Time Form Processing Documentation

• Loading .ui fileQUiLoader loader;QFile file("forms/textfinder.ui");file.open(QFile::ReadOnly);QWidget *formWidget = loader.load(&file, this);

• Locate objects in formui_okButton = qFindChild<QPushButton*>(this, "okButton");

Demo $QTDIR/examples/designer/calculatorbuilder

• Handle with care!

Qt Designer 62/96

http://qt.nokia.com/doc/latest/designer-using-a-ui-file.html#run-time-form-processing

Lab: Designer Order Form

• Create an order form dialog• With fields for price, quantity and total.• Total field updates itself to reflect quantity and price entered

Lab dialogs/lab-orderform

Qt Designer 63/96

Module: WidgetsCommon WidgetsLayout ManagementGuidelines for Custom Widgets

Widgets 64/96

Module Objectives

• Common Widgets• Text widgets• Value based widgets• Organizer widgets• Item based widgtes

• Layout Management• Geometry management• Advantages of layout managers• Qt’s layout managers• Size policies

• Custom Widgets• Rules for creating own widgets

Widgets 65/96

Module: Widgets

Common WidgetsLayout ManagementGuidelines for Custom Widgets

Widgets Common Widgets 66/96

Text Widgets

• QLabellabel = new QLabel("Text", parent);

• setPixmap( pixmap ) - as content• QLineEdit

line = new QLineEdit(parent);line->setText("Edit me");line->setEchoMode(QLineEdit::Password);connect(line, SIGNAL(textChanged(QString)) ...connect(line, SIGNAL(editingFinished()) ...

• setInputMask( mask ) - See Input Mask Documentation

• setValidator( validator ) - See Validator Documentation

• QTextEditedit = new QTextEdit(parent);edit->setPlainText("Plain Text");edit->append("<h1>Html Text</h1>");connect(edit, SIGNAL(textChanged(QString)) ...


http://qt.nokia.com/doc/latest/qlineedit.html#inputMask-prop

http://qt.nokia.com/doc/latest/qlineedit.html#setValidator

Button Widgets

• QAbstractButton• Abstract base class of buttons

• QPushButtonbutton = new QPushButton("Push Me", parent);button->setIcon(QIcon("images/icon.png"));connect(button, SIGNAL(clicked()) ...

• setCheckable(bool) - toggle button• QRadioButton

radio = new QRadionButton("Option 1", parent);

• QCheckBoxcheck = new QCheckBox("Choice 1", parent);

• QButtonGroup - non-visual button managergroup = new QButtonGroup(parent);group->addButton(button); // add more buttonsgroup->setExclusive(true);connect(group, SIGNAL(buttonClicked(QAbstractButton*)) ...


Value Widgets

• QSliderslider = new QSlider(Qt::Horizontal, parent);slider->setRange(0, 99);slider->setValue(42);connect(slider, SIGNAL(valueChanged(int)) ...

• QProgressBarprogress = new QProgressBar(parent);progress->setRange(0, 99);progress->setValue(42);// format: %v for value; %p for percentageprogress->setFormat("%v (%p%)");

• QSpinBoxspin = new QSpinBox(parent);spin->setRange(0, 99);spin->setValue(42);spin->setSuffix(" USD");connect(spin, SIGNAL(valueChanged(int)) ...


Organizer Widgets

• QGroupBoxbox = new QGroupBox("Your Options", parent);// ... set layout and add widgets

• setCheckable( bool ) - checkbox in title• QTabWidget

tab = new QTabWidget(parent);tab->addWidget(widget, icon, "Tab 1");connect(tab, SIGNAL(currentChanged(int)) ...

• setCurrentWidget( widget )• Displays page assoziated by widget

• setTabPosition( position )• Defines where tabs are drawn

• setTabsClosable( bool )• Adds close buttons


Item Widgets

• QComboBoxcombo = new QComboBox(parent);combo->addItem("Option 1", data);connect(combo, SIGNAL(activated(int)) ...QVariant data = combo->itemData(index);

• setCurrentIndex( index )• QListWidget

list = new QListWidget(parent);list->addItem("Item 1");// ownership of items with listitem = new QListWidgetItem("Item 2", list);item->setCheckState(Qt::Checked);connect(list, SIGNAL(itemActivated(QListWidgetItem*)) ...

• QListWidgetItem::setData(Qt::UserRole, data)

• Other Item Widgets: QTableWidget, QTreeWidget


Other Widgets

• QToolBox• Column of tabbed widget items

• QDateEdit, QTimeEdit, QDateTimeEdit• Widget for editing date and times

• QCalendarWidget• Monthly calendar widget

• QToolButton• Quick-access button to commands

• QSplitter• Implements a splitter widget

• QStackedWidget• Stack of widgets• Only one widget visible at a time

See Widget Classes Documentation


http://qt.nokia.com/doc/latest/gallery.html

Module: Widgets


Widgets Layout Management 73/96

Doing it Yourself

• Place and resize widgets• move()• resize()• setGeometry()

• Example:QWidget *parent = new QWidget(...);parent->resize(400,400);

QCheckBox *cb = new QCheckBox(parent);cb->move(10, 10);


Making Qt do the Work

DefinitionLayout: Specifying the relations of elements to each otherinstead of the absolute positions and sizes.

• Advantages:• Works with different languages.• Works with different dialog sizes.• Works with different font sizes.• Better to maintain.

• Disadvantage• Need to think about your layout first.

Thinking about layout is not really a disadvantage!


Managed Widgets and Sizes

• On managed widgets never call• setGeometry(), resize(), or move()

• Preferred• Override

• sizeHint()• minimumSizeHint()

• Or call• setFixedSize()• setMinimumSize()• setMaximumSize()


Layout Management Classes

• QHBoxLayout• Lines up widgets horizontally

• QVBoxLayout• Lines up widgets vertically

• QGridLayout• Arranges the widgets in a grid

• QFormLayout• Lines up a (label, widget) pairs in two columns.

• QStackedLayout• Arranges widgets in a stack

• only topmost is visible


QHBoxLayout and QVBoxLayout

• Lines up widgets horizontally or vertically• Divides space into boxes• Each managed widgets fills in one box

QWidget* window = new QWidget;QPushButton* one = new QPushButton("One");...QHBoxLayout* layout = new QHBoxLayout;layout->addWidget(one);...window->setLayout(layout);

example $QTDIR/examples/layouts/basiclayouts ( Seecreate[H,V]BoxLayout() )


Widgets in a grid - QGridLayout

QWidget* window = new QWidget;QPushButton* one = new QPushButton("One");

QGridLayout* layout = new QGridLayout;layout->addWidget(one, 0, 0); // row:0, col:0layout->addWidget(two, 0, 1); // row:0, col:1// row:1, col:0, rowSpan:1, colSpan:2layout->addWidget(three, 1, 0, 1, 2);

window->setLayout(layout)

• Additional• setColumnMinimumWidth() (minimum width of column)• setRowMinimumHeight() (minimum height of row)

• No need to specifyrows and columns before adding children.

Demo widgets/ex-layouts ( See createGridLayout() )


QFormLayout

• A two-column layout• Column 1 a label (as annotation)• Column 2 a widget (as field)

• Respects style guide of individual platforms.QWidget* window = new QWidget();QPushButton* one = new QPushButton("One");...QFormLayout* layout = new QFormLayout();layout->addRow("One", one);...window->setLayout(layout)

Demo widgets/ex-layouts ( See createFormLayout() )• Form layout with cleanlooks and mac style


Lab: Contact Form

• Specified by graphic designer• Your task: implement it• Focus on correct layout• Details disabled by default• ’Show Details’ enables details

Optional:• Click on Picture

• Lets user choose image• See lab description

• Validate Zip-Code as integersLab widgets/lab-contactform

Firstname Lastname

Zip-Code Town

Picture(128x128)

Contact

Details

[ ] Show Details


Some Layout Terms

• Stretch• Relative resize factor• QBoxLayout::addWidget(widget, stretch)• QBoxLayout::addStretch(stretch)• QGridLayout::setRowStretch(row, stretch)• QGridLayout::setColumnStretch(col, stretch)

• Contents Margins• Space reserved around the managed widgets.• QLayout::setContentsMargins(l,t,r,b)

• Spacing• Space reserved between widgets• QBoxLayout::addSpacing(size)


More Layout Terms

• Strut• Limits perpendicular box dimension• e.g. height for QHBoxLayout• Only for box layouts

• Min, max and fixed sizes• QWidget::setMinimumSize( QSize )• QWidget::setMaximumSize( QSize )• QWidget::setFixedSize( QSize )• Individual width and height contraints also available

• Nested Layouts• Allows flexible layouts• QLayout::addLayout(...)


Widgets Size Policies

• QSizePolicy describes interest of widget in resizingQSizePolicy policy = widget->sizePolicy();policy.setHorizontalPolicy(QSizePolicy::Fixed);widget->setSizePolicy(policy);

• One policy per direction (horizontal and vertical)• Button-like widgets set size policy to the following:

• may stretch horizontally• are fixed vertically• Similar to QLineEdit, QProgressBar, ...

• Widgets which provide scroll bars (e.g. QTextEdit)• Can use additional space• Work with less than sizeHint()

• sizeHint(): recommended size for widget


Available Size PoliciesPolicy sizeHint() Widget

Fixedauthoritative can not grow or shrink

Minimumminimal, suffi-cient

can expand, no advantage ofbeing larger

Maximumis maximum can shrink

Preferredis best can shrink, no advantage of

being larger

MinimumExpanding

is minimum can use extra space

Expandingsensible size can grow and shrink


Lab: Layout of buttons

• Develop the following layouts• Adjust the layouts as shown below.• Optionally:

• Make buttons resize vertically when making the window higher.

Lab widgets/lab-layoutbuttons



• How do you change the minimum size of a widget?• Name the available layout managers.• How do you specify stretch?• When are you allowed to call resize and move on a widget?


Module: Widgets


Widgets Guidelines for Custom Widgets 88/96

Guidelines: Creating a Custom Widget

• It’s as easy as deriving from QWidgetclass CustomWidget : public QWidget{public:explicit CustomWidget(QWidget* parent=0);

}

• If you need custom Signal Slots• add Q_OBJECT

• Use layouts to arrange widgets inside, or paint the widgetyourself.


Guidelines: Base class and Event Handlers• Do not reinvent the wheel

• See Widget Gallery Documentation

• Decide on a base class• Often QWidget or QFrame

• Overload needed event handlers• Often:

• QWidget::mousePressEvent(),QWidget::mouseReleaseEvent()

• If widget accepts keyboard input• QWidget::keyPressEvent()

• If widget changes appearance on focus• QWidget::focusInEvent(),

QWidget::focusOutEvent()


http://qt.nokia.com/doc/latest/gallery.html

Guidelines: Drawing a Widget

• Decide on composite or draw approach?• If composite: Use layouts to arrange other widgets• If draw : implement paint event

• Reimplement QWidget::paintEvent() for drawing• To draw widget’s visual appearance• Drawing often depends on internal states

• Decide which signals to emit• Usually from within event handlers• Especially mousePressEvent() or mouseDoubleClickEvent()

• Decide carefully on types of signal parameters• General types increase reusability• Candidates are bool, int and const QString&


Guidelines: Internal States and Subclassing

• Decide on publishing internal states• Which internal states should be made publically accessible?• Implement accessor methods

• Decide which setter methods should be slots• Candidates are methods with integral or common parameters

• Decide on allowing subclassing• If yes

• Decide which methods to make protected instead of private• Which methods to make virtual


Guidelines: Widget Constructor

• Decide on parameters at construction time• Enrich the constructor as necessary• Or implement more than one constructor• If a parameter is needed for widget to work correctly

• User should be forced to pass it in the constructor

• Keep the Qt convention with:explicit Constructor(..., QWidget *parent = 0)


Lab: File Chooser• Create a reusable file chooser component• 2 Modes

• Choose File• Choose Directory

• Think about the Custom Widget Guidelines!• Create a reusable API for a FileChooser?

Lab widgets/lab-filechooser

• After lab discuss your API


Lab: Compass Widget

• Implement a “compass widget” and let user ...• Select a direction

• north, west, south, east• and optionally none

• Provide API to ...• change direction programmatically• get informed when direction changes

• Optional• Add direction None• Select direction with the keyboard

Lab widgets/lab-compasswidget


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Nokia, the Nokia logo, Qt, and the Qt logo are trademarks of NokiaCorporation and/or its subsidiaries in Finland and other countries. Allother company, product, or service names may be trademarks orservice marks of others and are the property of their respectiveowners. The use of the word partner does not imply a partnershiprelationship between Nokia and any other company.

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