[次: Tulip Container クラス]

Qt 4 の新機能

このドキュメントは Qt 3 と Qt 4 の最も重要な違いをカバーしています。これは包括的なポーティングガイドを意図しているものではなく、あなたが遭遇するであろう最も重要な移植性に関して述べています。また、Qt3からの互換性サポートについて説明します。

• New Technologies in Qt 4
• Recent Additions to Qt 4
• Significant Improvements
• ビルド機構
• Include構文
• 名前空間
• QObject/QWidget コンストラクタ
• 動的キャスト
• QPointer<T>
• 描画イベント
• Qt3サポート層

New Technologies in Qt 4

Qt 4 では以下のコアテクノロジーが導入されています：

• Tulip, 新しいテンプレートコンテナクラスのセット
• Interviewアイテム表示のためのモデル／ビュー アーキテクチャ
• Arthur, Qt 4 描画フレームワーク
• Scribe低レベルテキストレイアウトのためのUnicodeテキスト表示用のPUBLICなAPI
• Mainwindowモダンなアクションベースのメインウインドウ、ツールバー、メニュー、およびドッキングアーキテクチャ
• 新しい Qt Designer ユーザーインターフェースのデザインツール

Recent Additions to Qt 4

以下の新機能は Qt 4 の最初のリリース後に Qt に追加されたものです：

In Qt 4.3:

• Support for different main window paradigms and styles, such as those found in Visual Studio or KDevelop.
• インタラクティブなグラフィックを提供する QtScript module, providing support for application scripting with ECMAScript.
• Improved graphics features, including an experimental Direct3D paint engine and improved provision for hardware accelerated rendering with OpenGL, and support for OpenGL ES in Qt for Embedded Linux.
• Scalable Vector Graphics (SVG) export, allowing SVG drawings to be created using the standard QPainter API.
• Support for arbitrary matrix transformations and set operations on painter paths.
• Native look and feel on Windows Vista; improved look and feel on Mac OS X.
• An improved Multiple Document Interface (MDI) implementation.
• Continuous improvements to Qt Designer, including support for dynamic properties.
• Support for Secure Socket Layer (SSL) communications via the QSslSocket class.
• Support for XML Localization Interchange File Format (XLIFF) files in Qt Linguist.
• A new font subsystem for Qt for Embedded Linux.

In Qt 4.2:

• インタラクティブなグラフィックを提供する Graphics View フレームワーク
• Desktop integration facilities for applications.
• Qt Style Sheets enable easy, yet powerful customization of user interfaces.
• Support for the D-Bus Inter-Process Communication (IPC) and Remote Procedure Calling (RPC) mechanism.
• An Undo framework based on the Command pattern.
• Support for model-based text completion in standard and custom widgets.
• New widgets and GUI features, such as QCalendarWidget and QGLFramebufferObject.
• Classes to provide higher level application infrastructure, such as QFileSystemWatcher and QDataWidgetMapper.

In Qt 4.1:

• Integrated support for rendering Scalable Vector Graphics (SVG) drawings and animations.
• Support for child widget transparency on all platforms.
• A Portable Document Format (PDF) backend for Qt's printing system.
• A unit testing framework for Qt applications and libraries.
• Modules for extending Qt Designer and dynamic user interface building.
• New proxy models to enable view-specific sorting and filtering of data displayed using item views.
• Support for universal binaries on Mac OS X.
• Additional features for developers using OpenGL, such as support for pixel and sample buffers.
• A flexible syntax highlighting class based on the Scribe rich text framework.
• Support for network proxy servers using the SOCKS5 protocol.
• Support for OLE verbs and MIME data handling in ActiveQt.

For more information about improvements in the current release, see the detailed list of changes.

Significant Improvements

The following modules have been significantly improved for Qt 4:

• A fully cross-platform accessibility module, with support for the emerging SP-API Unix standard in addition to Microsoft and Mac Accessibility.
• The SQLモジュール, which is now based on the Interview model/view framework.
• The network module, with better support for UDP and synchronous sockets.
• The style API, which is now decoupled from the widgets, meaning that you can draw any user interface element on any device (widget, pixmap, etc.).
• Enhanced thread support, with signal-slot connections across threads and per-thread event loops.
• A new resource system for embedding images and other resource files into the application executable.

Build System

Unlike previous Qt releases, Qt 4 is a collection of smaller libraries:

QtCore contains tool classes like QString, QList, and QFile, as well as kernel classes like QObject ではなく QTimer. The QApplication class has been refactored so that it can be used in non-GUI applications. It is split into QCoreApplication (in QtCore) and QApplication (in QtGui).

This split makes it possible to develop server applications using Qt without linking in any unnecessary GUI-related code and without requiring GUI-related system libraries to be present on the target machine (e.g. Xlib on X11, Carbon on Mac OS X).

If you use qmake to generate your makefiles, qmake will by default link your application against QtCore ではなく QtGui. To remove the dependency upon QtGui, add the line

 QT -= gui

to your .pro file. To enable the other libraries, add the line

 QT += network opengl sql qt3support

Another change to the build system is that moc now understands preprocessor directives. qmake automatically passes the defines set for your project (using "DEFINES +=") on to moc, which has its own built-in C++ preprocessor.

To compile code that uses .ui files, you will also need this line in the .pro file:

 CONFIG += uic3

Include Syntax

The syntax for including Qt class definitions has become

 #include <QClassName>

For example:

 #include <QString>
 #include <QApplication>
 #include <QSqlTableModel>

This is guaranteed to work for any public Qt class. The old syntax,

 #include <qclassname.h>

still works, but we encourage you to switch to the new syntax.

If you attempt to include a header file from a library that isn't linked against the application, this will result in a compile-time warning (e.g., "QSqlQuery: No such file or directory"). You can remedy to this problem either by removing the offending include or by specifying the missing library in the QT entry of your .pro ファイルの QT エントリに加えることで回避できる. (上記の Build System を見よ)

ライブラリの名前を単純に記述することで、ライブラリに含まれる全てのクラス定義をインクルードすることができる. 例:

 #include <QtCore>

名前空間

Qt 2 introduced a class called Qt for global-like constants (e.g., Qt::yellow) が導入された. Qt 2 がリリースされた当時には C++ の名前空間を扱えないコンパイラもあったので、名前空間の導入は見送られていた.

Qt 4 では、この Qt クラスは 名前空間 Qt に取って代えられる. 名前空間 Qt 内にある定数にアクセスするには、プレフィクス Qt::: (e.g., Qt::yellowとする) か、

 using namespace Qt;

という指令をソースファイルの先頭、 #include 指令の後に追加すること. using namespace syntax you don't need the prefix (e.g., yellow で十分である)

Qt 3 アプリケーションを移植する場合、これに関連したソースコードの互換性問題に遭遇するおそれがある. たとえば、Qt 3 ではたとえば、Qt 3 では QWidget::yellow の代わりに Qt::yellowと書くことができた. しかし QWidget -これはQTから継承されていて、Qt4では動かない。そのため Qt::yellow と書きなおすか、あるいは"using namespace" 指令を追加して Qt::プレフィクスを取り除くかしなければならない.

この qt3to4 porting tool automates this conversion.

QObject/QWidget コンストラクタ

Qt4で、私たちは QObject/QWidget サブクラスのコンストラクタを簡素化しようとしました。 これは、サブクラス化をより簡単にして、それと同時にQtライブラリをより効率的にするのを助けます。

コンストラクタは「const char *name」を引数に取らなくなりました。もし、貴方が名前を QObjectに付けたければ、貴方は、 QObject::setObjectName(const QString & name)メソッドをインスタンス化の後に実行しなければなりません。オブジェクトの名前は QString. The reasons for this change are:

• Code that used it looked confusing, for example:

   QLabel *label1 = new QLabel("Hello", this);
   QLabel *label2 = new QLabel(this, "Hello");

  label1 is a QLabel that displays the text "Hello"; label2 is a QLabel with no text, with the object name "Hello".

• From surveys we did, most users didn't use the name, although they blindly followed Qt's convention and provided a "const char *name" in their subclasses's constructors. For example:

   MyWidget::MyWidget(QWidget *parent, const char *name)
       : QWidget(parent, name)
   {
       ...
   }

• The name parameter was in Qt since version 1, and it always was documented as: "It is not very useful in the current version of Qt, but it will become increasingly important in the future." Ten years later, it still hasn't fulfilled its promise.

QWidget's WFlags data type has been split in two: Qt::WindowFlags specifies low-level window flags (the type of window and the frame style), whereas Qt::WidgetAttribute specifies various higher-level attributes about the widget (e.g., WA_StaticContents). Widget attributes can be set at any time using QWidget::setAttribute(); low-level window flags can be passed to the QWidget constructor or set later using QWidget::setParent(). As a consequence, the constructors of most QWidget subclasses don't need to provide a WFlags parameter.

The parent parameter of all QObject classes in Qt defaults to a 0 pointer, as it used to do in Qt 1. This enables a style of programming where widgets are created without parents and then inserted in a layout, at which point the layout automatically reparents them.

動的キャスト

Qt 4 provides a qobject_cast<>() function that performs a dynamic cast based on the meta-information generated by moc for QObject subclasses. Unlike the standard C++ dynamic_cast<>() construct, qobject_cast<>() works even when RTTI is disabled, and it works correctly across DLL boundaries.

Here's the Qt 3 idiom to cast a type to a subtype:

 // DEPRECATED
 if (obj->inherits("QPushButton")) {
     QPushButton *pushButton = (QPushButton *)obj;
     ...
 }

The Qt 4 idiom is both cleaner and safer, because typos will always result in compiler errors:

 QPushButton *pushButton = qobject_cast<QPushButton *>(obj);
 if (pushButton) {
     ...
 }

QPointer<T>

The QPointer<T> class provides a pointer to type T (where T inherits from QObject) that is automatically set to 0 when the referenced object is destroyed. Guarded pointers are useful whenever you want to store a pointer to an object you do not own.

Example:

 QLabel *label = new QLabel;
 QPointer<QLabel> safeLabel = label;
 safeLabel->setText("Hello world!");
 delete label;
 // safeLabel is now 0, whereas label is a dangling pointer

QPointer<T> is more or less the same as the old QGuardedPtr<T> class, except that it is now implemented in a much more lightweight manner than before. The cost of one QPointer<T> object is now approximately the same as that of a signal--slot connection.

描画イベント

Qt 4はプラットフォーム透過なダブルバッファリングをサポートします．この特徴は，QWidget::setAttribute(Qt::WA_PaintOnScreen)を呼ぶことでウィジェットごとに機能を止めることができます．

この結果，すべての描画はpaintEvent()関数から行なわなければなりません（原文：must be done）．これはMac OS XのHIView APIでも同様です．実際には，これはほとんど問題にはなりません．なぜなら描画イベントをつくる（原文：create paint event）ために，更新領域を引数にupdate()をコード内のどこからでも呼ぶことができるからです．

ポーティングを助けるために， QWidget は Qt::WA_PaintOutsidePaintEvent 属性をサポートします．この属性はWindowsやX11で paintEvent() on Windows and X11.

Qt3サポート層

Qt 4 provides an extension library that applications based on Qt 3, called Qt3Support, that Qt applications can link against. This allows for more compatibility than ever before, without bloating Qt.

• Classes that have been replaced by a different class with the same name, such as QListView, and classes that no longer exist in Qt 4 are available with a 3 in their name (e.g., Q3ListView, Q3Accel)を呼ぶことでウィジェットごとに機能を止めることができます．
• Other classes provide compatibility functions. Most of these are implemented inline, so that they don't bloat the Qt libraries.

To enable the Qt 3 support classes and functions, add the line

 QT += qt3support

to your .pro file.

On Visual C++ 7 and GCC 3.2+, using compatibility functions often results in a compiler warning (e.g., "'find' is deprecated"). If you want to turn off that warning, add the line

 DEFINES += QT3_SUPPORT

to your .pro file.

If you want to use compatibility functions but don't want to link against the Qt3Support library, add the line

 DEFINES += QT3_SUPPORT_WARNINGS

or

 DEFINES += QT3_SUPPORT

to your .pro file, depending on whether you want compatibility function calls to generate compiler warnings or not.

[Next: The Tulip Container Classes]