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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/4.2/designer-manual.html user documentation]. 
It might make sense to provide a brief example of using Designer here, but
for now I 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*)</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.  There are a few ways
to do this; for now I will only discuss one method, in which we create a class
that inherits from both <tt>Ui::MyDialog</tt> and a Qt container class
like {{qt|QFrame}}.  Create a class definition file named
"<tt>mydialog.h</tt>", and add the following:
<code cppqt>
#ifndef MYDIALOG_H
#define MYDIALOG_H
#include <KDialog>
#include "ui_mydialog.h"
class MyDialogUI : public QFrame, public Ui::MyDialog
        MyDialogUI( QWidget *parent=0 );
class MyDialog : public KDialog
        MyDialog( QWidget *parent=0 );
    private slots:
        void slotButtonClicked();
        MyDialogUI *ui;
So we have defined two classes.  <tt>MyDialogUI</tt> is simply a
{{qt|QFrame}} with your UI elements placed inside it. 
<tt>MyDialog</tt> is a {{class|KDialog}} window, whose main
widget will be the <tt>MyDialogUI</tt> instance named
<tt>ui</tt> above. Here is the "<tt>mydialog.cpp</tt>"
C++ definition file:
<code cppqt>
#include <KLocale>
#include <KMessageBox>
#include "mydialog.h"
MyDialogUI::MyDialogUI( QWidget *parent )
: QFrame( parent )
    setupUi( this );
MyDialog::MyDialog( QWidget *parent )
: KDialog( parent )
    ui = new MyDialogUI( this );
    setMainWidget( ui );
    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 widgets.
    connect( ui->MyButton, SIGNAL( clicked() ),
            this, SLOT( slotButtonClicked() ) );
    delete ui;
void MyDialog::slotButtonClicked()
    KMessageBox::information( this,
                              i18n("You pressed the button!" ),
                              i18n( "Hooray!" ) );
#include "mydialog.moc"
So, basically, we call <tt>setupUi(this)</tt> in the <tt>MyDialogUI</tt>
constructor, which places your UI elements into that widget.  Then, in the
<tt>MyDialog</tt> constructor, we create the <tt>MyDialogUI</tt>
instance named <tt>ui</tt> and set it to be our dialog's main widget.
We can then interact with all of the UI elements by prepending
"<tt>ui-></tt>" to their names.
=== Final Thoughts ===
The cascade of files and classes in this tutorial may seem daunting at
first, but the naming scheme I've layed out here has one nice intuitive
feature: the three source code files that you will be editing
directly (either as text or with Designer) are all named with the same
simple filename stem: <tt>mydialog.ui</tt>, <tt>mydialog.h</tt>, and
<tt>mydialog.cpp</tt>.  Just remember that you'll be using the
<tt>MyDialog</tt> class almost exclusively.  Setting up the
<tt>MyDialogUI</tt> class is easy (it only contains a one-line
constructor), and once it's set up you can pretty well ignore it.

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.