Difference between revisions of "Development/Tutorials/Using Qt Designer"

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== Qt Designer User Interfaces in KDE ==
{{Note|This is now located at https://community.kde.org/Get_Involved/development/Tutorials/Using_Qt_Designer}}
In this tutorial, we will explore how to programatically insert user interfaces
(UIs) created with Qt Designer, into your KDE project. 
== Designing the UI ==
[http://www.trolltech.com/products/qt/features/designer Qt Designer] is a
graphical program which allows you to easily build user interfaces, using an
intuitive "drag n drop" interface.  Designer has its own excellent
[http://doc.trolltech.com/4.3/designer-manual.html user documentation]. 
It might make sense to provide a brief example of using Designer here, but
for now this article will leave most of that to the Designer manual itself.
== Adding the UI File to Your KDE Project ==
For our purposes, the most important part of using Designer is the
<tt>*.ui</tt> file that it creates.  This is simply an XML file that
encodes the user interface in a machine-readable (and human-readable!) way.
Let's imagine that you've created a UI named "MyDialog" with Designer, and
saved it as the file <tt>mydialog.ui</tt>.  To add this UI to your KDE
project, simply add a command like the following to your CMakeLists.txt file:
kde4_add_ui_files(myapp_SRCS mydialog.ui)
Replace "<tt>myapp_SRCS</tt>" with the name of the main block in
your CMakeLists.txt file, defining all of the source code files.  It is usually the
name of your application, with "<tt>_SRCS</tt>" appended.
When you do this, the build system will run the Qt program <tt>uic</tt>
on <tt>mydialog.ui</tt>, to auto-generate a C++ header file that
defines the UI.  The generated file will be named <tt>ui_mydialog.h</tt>.
== Using the UI in Your Code ==
The <tt>ui_mydialog.h</tt> file defines a class named
"<tt>Ui_MyDialog</tt>", that contains all of the widgets you created in
Designer as public members of the class.  It also contains the public function
"<tt>setupUi(QWidget *parent)</tt>", which instantiates all of the widgets,
sets up their properties, and inserts them into layout managers, all according
to what you specified in Designer.
Note that <tt>setupUi()</tt> takes a <tt>QWidget*</tt>
argument.  This argument represents the parent container widget, into which
all of the widgets in your UI will be inserted.  In other words,
'''<tt>Ui_MyDialog</tt> is not itself derived from QWidget''', and
'''it does not contain a toplevel widget itself'''.  You have to supply the toplevel widget
when you call <tt>setupUi()</tt>.  This is an important point.
One more important semantic detail:  the <tt>Ui_MyDialog</tt> class
also creates a <tt>Ui</tt> namespace, which simply creates an alias
for the class.  So you can use <tt>Ui::MyDialog</tt> to refer to the
same class.
Now, on to actually using the generated UI in your code. The Qt documentation
shows three ways of [http://doc.trolltech.com/latest/designer-using-a-component.html how to use ui-files];
here only the ''direct approach'' is discussed. The goal is to create a KDialog
which embeds the UI from the ui-file. First, we have to subclass MyDialog from
KDialog and add a pointer to Ui::MyDialog. The header file of
"<tt>mydialog.h</tt>" looks like the following:
<code cppqt>
#ifndef MYDIALOG_H
#define MYDIALOG_H
#include <KDialog>
// include the automatically generated header file for the ui-file
#include "ui_mydialog.h"
class MyDialog : public KDialog
        MyDialog( QWidget *parent=0 );
    private slots:
        void slotButtonClicked();
        // pointer to the ui. we can access all gui elements
        // specified in Designer. If mydialog.ui contains a
        // button "myButton", we will be able to access it
        // with ui.myButton in the cpp file.
        Ui::MyDialog ui;
Now we are going to look at the implementation of MyDialog, which is in the file
<code cppqt>
#include <KLocale>
#include <KMessageBox>
// include the header file of the dialog
#include "mydialog.h"
MyDialog::MyDialog( QWidget *parent )
: KDialog( parent )
    QWidget *widget = new QWidget( this );
    // create the user interface, the parent widget is "widget"
    ui.setupUi(widget); // this is the important part
    // set the widget with all its gui elements as the dialog's
    // main widget
    setMainWidget( widget );
    // other KDialog options
    setCaption( i18n("This is my Dialog window!") );
    setButtons( KDialog::Close );
    // Example Signal/Slot connection using widgets in your UI.
    // Note that you have to prepend "ui." when referring
    // to your UI elements.
    connect( ui.myButton, SIGNAL( clicked() ),
            this, SLOT( slotButtonClicked() ) );
void MyDialog::slotButtonClicked()
    KMessageBox::information( this,
                              i18n("You pressed the button!" ),
                              i18n( "Hooray!" ) );
#include "mydialog.moc"
So, basically, we create a new Ui::MyDialog and then call
<tt>ui.setupUi(widget)</tt> in the constructor of <tt>MyDialog</tt>. This
places the UI elements into the given widget. Then we set the parent-widget
as the KDialog's main widget. We can then interact with all of the UI elements
by prepending "<tt>ui.</tt>" to their names, just like it is often done
with the prefix "<tt>m_</tt>".
== Final Thoughts ==
The cascade of files and classes in this tutorial may seem daunting at
first, but the naming scheme layed out here has one nice intuitive
feature: the source code files that you will be editing directly (either as
text or with Designer) are all named with the same scheme:
* '''mydialog.ui''': the user interface, created with Designer
* '''ui_mydialog.h''': auto-generated by uic, Qt's user interface compiler
* '''mydialog.h/cpp''': the dialog implementation
The steps in short are
# create <tt>mydialog.ui</tt>
# create <tt>mydialog.h/cpp</tt>
# add variable Ui::MyDialog ui; in <tt>mydialog.h</tt>
# call ui.setupUi(widget);</tt>
# access the ui elements with <tt>ui.</tt>
== Qt Documentation ==
The Qt documentation contains a good article about
[http://doc.trolltech.com/latest/designer-using-a-component.html Using a Component in Your Application].

Latest revision as of 12:48, 16 May 2019

This page was last edited on 16 May 2019, at 12:48. Content is available under Creative Commons License SA 4.0 unless otherwise noted.