source: trunk/doc/src/porting/porting4-designer.qdoc

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/*!
    \page porting4-designer.html
    \title Porting UI Files to Qt 4
    \contentspage {Porting Guides}{Contents}
    \previouspage Porting to Qt 4 - Drag and Drop
    \nextpage Porting to Graphics View
    \ingroup porting
    \brief Information about changes to the UI file format in Qt 4.

    Qt Designer has changed significantly in the Qt 4 release. We
    have moved away from viewing Qt Designer as an IDE and
    concentrated on creating a robust form builder which can be
    extended and embedded in existing IDEs. Our efforts are ongoing
    and include the \l{Visual Studio Integration},
    as well as integrating Designer with KDevelop and possibly other
    IDEs.

    The most important changes in Qt Designer 4 which affect porting
    for UI files are summarized below:

    \list
    \o  \bold{Removed project manager.}
        Qt Designer now only reads and edits UI
        files. It has no notion of a project file (\c .pro).

    \o  \bold{Removed code editor.}
        Qt Designer can no longer be used to edit source files.

    \o  \bold{Changed format of UI files.}
        Qt Designer 4 cannot read files created by Qt Designer 3 and
        vice versa. However, we provide the tool \c uic3 to generate Qt
        4 code out of Qt 3 UI files, and to convert old UI files
        into a format readable by Qt Designer 4.

    \o  \bold{Changed structure of the code generated by \c uic.}
        The \c myform.ui file containing the form \c MyForm is now
        converted into a single header file \c ui_myform.h, which
        contains the declaration and inline definition of a POD class
        \c Ui::MyForm.

    \o  \bold{New resource file system.} Icon data is no longer
        stored in the UI file. Instead, icons are put into resource
        files (\c .qrc).
    \endlist

    The rest of this document explains how to deal with the main
    differences between Qt Designer 3 and Qt Designer 4:

    \tableofcontents

    See \l{Porting to Qt 4} and \l{qt3to4 - The Qt 3 to 4 Porting
    Tool} for more information about porting from Qt 3 to Qt 4. See
    also the \l{Qt Designer Manual}.

    \section1 uic Output

    In Qt 3, \c uic generated a header file and an implementation for
    a class, which inherited from one of Qt's widgets. To use the
    form, the programmer included the generated sources into the
    application and created an instance of the class.

    In Qt 4, \c uic creates a header file containing a POD class. The
    name of this class is the object name of the main container,
    qualified with the \c Ui namespace (e.g., \c Ui::MyForm). The
    class is implemented using inline functions, removing the need of
    a separate \c .cpp file. Just as in Qt 3, this class contains
    pointers to all the widgets inside the form as public members. In
    addition, the generated class provides the public method \c
    setupUi().

    The class generated by \c uic is not a QWidget; in fact, it's not
    even a QObject. Instead, it is a class which knows how to
    populate an instance of a main container with the contents of the
    form. The programmer creates the main container himself, then
    passes it to \c setupUi().

    For example, here's the \c uic output for a simple \c
    helloworld.ui form (some details were removed for simplicity):

    \snippet doc/src/snippets/code/doc_src_porting4-designer.qdoc 0

    In this case, the main container was specified to be a QWidget
    (or any subclass of QWidget). Had we started with a QMainWindow
    template in Qt Designer, \c setupUi()'s parameter would be of
    type QMainWindow.

    There are two ways to create an instance of our form. One
    approach is to create an instance of the \c Ui::HelloWorld class,
    an instance of the main container (a plain QWidget), and call \c
    setupUi():

    \snippet doc/src/snippets/code/doc_src_porting4-designer.qdoc 1

    The second approach is to inherit from both the \c Ui::HelloWorld
    class and the main container, and to call \c setupUi() in the
    constructor of the subclass. In that case, QWidget (or one of
    its subclasses, e.g. QDialog) must appear first in the base class
    list so that \l{moc} picks it up correctly. For example:

    \snippet doc/src/snippets/code/doc_src_porting4-designer.qdoc 2

    This second method is useful when porting Qt 3 forms to Qt 4. \c
    HelloWorldWidget is a class whose instance is the actual form
    and which contains public pointers to all the widgets in it. It
    therefore has an interface identical to that of a class generated
    by \c uic in Qt 3.

    Creating POD classes from UI files is more flexible and
    generic than the old approach of creating widgets. Qt Designer
    does not need to know anything about the main container apart from
    the base widget class it inherits. Indeed, \c Ui::HelloWorld can
    be used to populate any container that inherits QWidget.
    Conversely, all non-GUI aspects of the main container may be
    implemented by the programmer in the application's sources
    without reference to the form.

    \section1 Working with uic3

    Qt 4 comes with the tool \c uic3 for working with old \c .ui
    files. It can be used in two ways:

    \list 1
    \o To generate headers and source code for a widget to implement any
    custom signals and slots added using Qt Designer 3.
    \o To generate a new UI file that can be used with Qt Designer 4.
    \endlist

    You can use both these methods in combination to obtain UI, header
    and source files that you can use as a starting point when porting
    your user interface to Qt 4.

    The first method generates a Qt 3 style header and implementation
    which uses Qt 4 widgets (this includes the Qt 3 compatibility classes
    present in the Qt3Support library). This process should be familiar to
    anyone used to working with Qt Designer 3:

    \snippet doc/src/snippets/code/doc_src_porting4-designer.qdoc 3

    The resulting files \c myform.h and \c myform.cpp implement the
    form in Qt 4 using a QWidget that will include custom signals,
    slots and connections specified in the UI file. However,
    see below for the \l{#Limitations of uic3}{limitations} of this
    method.

    The second method is to use \c uic3 to convert a Qt Designer 3 \c .ui
    file to the Qt Designer 4 format:

    \snippet doc/src/snippets/code/doc_src_porting4-designer.qdoc 4

    The resulting file \c myform4.ui can be edited in Qt Designer 4. The
    header file for the form is generated by Qt 4's \c uic. See the
    \l{Using a Designer UI File in Your Application} chapter of the
    \l{Qt Designer Manual} for information about the preferred ways to
    use forms created with Qt Designer 4.

    \c uic3 tries very hard to map Qt 3 classes and their properties to
    Qt 4. However, the behavior of some classes changed significantly
    in Qt 4. To keep the form working, some Qt 3 classes are mapped
    to classes in the Qt3Support library. Table 1 shows a list of
    classes this applies to.

    \table
    \header \o Qt 3 class       \o Qt 4 class
    \row    \o \c QButtonGroup  \o Q3ButtonGroup
    \row    \o \c QDateEdit     \o Q3DateEdit
    \row    \o \c QDateTimeEdit \o Q3DateTimeEdit
    \row    \o \c QGroupBox     \o Q3GroupBox
    \row    \o \c QListBox      \o Q3ListBox
    \row    \o \c QListView     \o Q3ListView
    \row    \o \c QMainWindow   \o Q3MainWindow
    \row    \o \c QTextEdit     \o Q3TextEdit
    \row    \o \c QTextView     \o Q3TextView
    \row    \o \c QTimeEdit     \o Q3TimeEdit
    \row    \o \c QWidgetStack  \o Q3WidgetStack
    \row    \o \c QWizard       \o Q3Wizard
    \endtable

    \section1 Limitations of uic3

    Converting Qt 3 UI files to Qt 4 has some limitations. The
    most noticeable limitation is the fact that since \c uic no
    longer generates a QObject, it's not possible to define custom
    signals or slots for the form. Instead, the programmer must
    define these signals and slots in the main container and connect
    them to the widgets in the form after calling \c setupUi(). For
    example:

    \snippet doc/src/snippets/code/doc_src_porting4-designer.qdoc 5

    A quick and dirty way to port forms containing custom signals and
    slots is to generate the code using \c uic3, rather than \c uic. Since
    \c uic3 does generate a QWidget, it will populate it with custom
    signals, slots and connections specified in the UI file.
    However, \c uic3 can only generate code from Qt 3 UI files, which
    implies that the UI files never get translated and need to be
    edited using Qt Designer 3.

    Note also that it is possible to create implicit connections
    between the widgets in a form and the main container. After \c
    setupUi() populates the main container with child widgets it
    scans the main container's list of slots for names with the form
    \tt{on_\e{objectName}_\e{signalName}().}

    If the form contains a widget whose object name is
    \tt{\e{objectName}}, and if that widget has a signal called
    \tt{\e{signalName}}, then this signal will be connected to the
    main container's slot. For example:

    \snippet doc/src/snippets/code/doc_src_porting4-designer.qdoc 6

    Because of the naming convention, \c setupUi() automatically
    connects \c pushButton's \c clicked() signal to \c
    HelloWorldWidget's \c on_pushButton_clicked() slot.

    \section1 Icons

    In Qt 3, the binary data for the icons used by a form was stored
    in the UI file. In Qt 4 icons and any other external files
    can be compiled into the application by listing them in a \l{The
    Qt Resource System}{resource file} (\c .qrc). This file is
    translated into a C++ source file using Qt's resource compiler
    (\c rcc). The data in the files is then available to any Qt class
    which takes a file name argument.

    Imagine that we have two icons, \c yes.png and \c no.png. We
    create a resource file called \c icons.qrc with the following
    contents:

    \snippet doc/src/snippets/code/doc_src_porting4-designer.qdoc 7

    Next, we add the resource file to our \c .pro file:

    \snippet doc/src/snippets/code/doc_src_porting4-designer.qdoc 8

    When \c qmake is run, it will create the appropriate Makefile
    rules to call \c rcc on the resource file, and compile and link
    the result into the application. The icons may be accessed as
    follows:

    \snippet doc/src/snippets/code/doc_src_porting4-designer.qdoc 9

    In each case, the leading colon tells Qt to look for the file in
    the virtual file tree defined by the set of resource files
    compiled into the application instead of the file system.

    In the \c .qrc file, the \c qresource tag's \c prefix attribute
    is used to arrange the files into categories and set a virtual
    path where the files will be accessed.

    Caveat: If the resource file was not linked directly into the
    application, but instead into a dynamic or static library that
    was later linked with the application, its virtual file tree will
    not be available to QFile and friends until the Q_INIT_RESOURCE()
    macro is called. This macro takes one argument, which is the name
    of the \c .qrc file, without the path or the file extension. A
    convenient place to initialize resources is at the top of the
    application's \c main() function.

    In Qt Designer 4, we can associate any number of resource files
    with a form using the resource editor tool. The widgets in the
    form can access all icons specified in its associated resource
    files.

    In short, porting of icons from a Qt 3 to a Qt 4 form involves
    the following steps:

    \list 1
    \o Use \c{uic3 -convert} to obtain a UI file understood by
       Qt Designer 4.

    \o Create a \c .qrc file with a list of all the icon files.

    \o Add the resource file to the \c .pro file.

    \o Open the form in Qt Designer 4 and add the resource file to the
       form's resource editor.

    \o Set the icon properties for the appropriate widgets.
    \endlist

    \section1 Custom Widgets

    Qt Designer 3 supported defining custom widgets by specifying
    their name, header file and methods. In Qt Designer 4, a custom
    widget is always created by "promoting" an existing Qt widget to
    a custom class. Qt Designer 4 assumes that the custom widget will
    inherit from the widget that has been promoted. In the form
    editor, the custom widget will retain the looks, behavior,
    properties, signals and slots of the base widget. It is not
    currently possible to tell Qt Designer 4 that the custom widget
    will have additional signals or slots.

    \c{uic3 -convert} handles the conversion of custom widgets to the
    new \c .ui format, however all custom signals and slots are lost.
    Furthermore, since Qt Designer 3 never knew the base widget class
    of a custom widget, it is taken to be QWidget. This is often
    sufficient. If not, the custom widgets have to be inserted
    manually into the form.

    Custom widget plugins, which contain custom widgets to be used in
    Qt Designer, must themselves be ported before they can be used in
    forms ported with \c{uic3}.
    The \l{Porting to Qt 4} document contains information about general
    porting issues that may apply to the custom widget code itself, and
    the \l{Creating Custom Widgets for Qt Designer} chapter of the
    \l{Qt Designer Manual} describes how the ported widget should be
    built in order to work in Qt Designer 4.
*/