如何初始化 QML singleton？

Question

我在https://github.com/jh3010-qt-questions/font_test有一個簡單的測試項目，它演示了這個問題。

我有一個 label 定義為：

    Label // #1
    {
      text: "Pack my box with five dozen liquor jugs -- DEFAULT"
    }

應該使用 qtquickcontrols2.conf 中定義的默認字體（Art Brewery）顯示，但事實並非如此。

但是，如果我添加 Label：

    Label // #2
    {
      font.family: Fonts.robotoBold.name
      text: "Pack my box with five dozen liquor jugs -- Roboto Bold"
    }

然后，Label #1 將使用 Art Brewery 字體繪制。

正在發生的事情是 Fonts singleton 沒有被初始化，除非至少有一個引用它。

我的問題是：如何初始化 singleton？

我試過這樣的事情：

qmlRegisterSingletonType( QUrl( "file:///Users/jamesh/depot_qt/questions/font_test/assets/Fonts/Fonts.qml"), "Font", 1, 0, "Font" );

在我的 main.cpp 中，但它不起作用。

我的目錄結構如下：

$ tree font_test

font_test
├── README.md
├── assets
│   └── Fonts
│       ├── Art\ Brewery.ttf
│       ├── Fonts.qml
│       ├── Roboto-Bold.ttf
│       ├── Roboto-BoldItalic.ttf
│       ├── Roboto-Light.ttf
│       ├── Roboto-LightItalic.ttf
│       ├── Roboto-Medium.ttf
│       ├── Roboto-MediumItalic.ttf
│       ├── Roboto-Regular.ttf
│       ├── Roboto-RegularItalic.ttf
│       ├── RobotoMono-Bold.ttf
│       ├── RobotoMono-BoldItalic.ttf
│       ├── RobotoMono-Light.ttf
│       ├── RobotoMono-LightItalic.ttf
│       ├── RobotoMono-Medium.ttf
│       ├── RobotoMono-MediumItalic.ttf
│       ├── RobotoMono-Regular.ttf
│       ├── RobotoMono-RegularItalic.ttf
│       └── qmldir
├── font_test.pro
├── font_test.pro.user
├── main.cpp
├── main.qml
├── qml.qrc
└── qtquickcontrols2.conf

我的qtquickcontrols2.conf是

[Controls]
Style=Material

[Material]
Primary=White
Foreground=#444444
Accent=Blue
Theme=Light
Font\Family=Art Brewery

[Universal]
Theme=System

我的main.cpp是：

#include <QGuiApplication>
#include <QQmlApplicationEngine>

int main(int argc, char *argv[])
{
#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
  QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
#endif

  QGuiApplication app(argc, argv);

  QQmlApplicationEngine engine;

  engine.addImportPath( ":/" );

//  qmlRegisterSingletonType( QUrl( "file:///Users/jamesh/depot_qt/questions/font_test/assets/Fonts/Fonts.qml"), "Font", 1, 0, "Font" );

  const QUrl url(QStringLiteral("qrc:/main.qml"));

  QObject::connect( &engine,
                    &QQmlApplicationEngine::objectCreated,
                    &app,
                    [url](QObject *obj, const QUrl &objUrl )
                    {
                      if (!obj && url == objUrl)
                        QCoreApplication::exit(-1);
                    },
                    Qt::QueuedConnection);

  engine.load(url);

  return app.exec();
}

我的qml.qrc文件是：

<RCC>
    <qresource prefix="/">
        <file>main.qml</file>
        <file>qtquickcontrols2.conf</file>
    </qresource>
    <qresource prefix="/Fonts">

        <file alias="qmldir">assets/Fonts/qmldir</file>
        <file alias="Fonts.qml">assets/Fonts/Fonts.qml</file>

        <file alias="Art Brewery.ttf">assets/Fonts/Art Brewery.ttf</file>

        <file alias="Roboto-Bold.ttf">assets/Fonts/Roboto-Bold.ttf</file>
        <file alias="Roboto-BoldItalic.ttf">assets/Fonts/Roboto-BoldItalic.ttf</file>
        <file alias="Roboto-Light.ttf">assets/Fonts/Roboto-Light.ttf</file>
        <file alias="Roboto-LightItalic.ttf">assets/Fonts/Roboto-LightItalic.ttf</file>
        <file alias="Roboto-Medium.ttf">assets/Fonts/Roboto-Medium.ttf</file>
        <file alias="Roboto-MediumItalic.ttf">assets/Fonts/Roboto-MediumItalic.ttf</file>
        <file alias="Roboto-Regular.ttf">assets/Fonts/Roboto-Regular.ttf</file>
        <file alias="Roboto-RegularItalic.ttf">assets/Fonts/Roboto-RegularItalic.ttf</file>

        <file alias="RobotoMono-Bold.ttf">assets/Fonts/RobotoMono-Bold.ttf</file>
        <file alias="RobotoMono-BoldItalic.ttf">assets/Fonts/RobotoMono-BoldItalic.ttf</file>
        <file alias="RobotoMono-Light.ttf">assets/Fonts/RobotoMono-Light.ttf</file>
        <file alias="RobotoMono-LightItalic.ttf">assets/Fonts/RobotoMono-LightItalic.ttf</file>
        <file alias="RobotoMono-Medium.ttf">assets/Fonts/RobotoMono-Medium.ttf</file>
        <file alias="RobotoMono-MediumItalic.ttf">assets/Fonts/RobotoMono-MediumItalic.ttf</file>
        <file alias="RobotoMono-Regular.ttf">assets/Fonts/RobotoMono-Regular.ttf</file>
        <file alias="RobotoMono-RegularItalic.ttf">assets/Fonts/RobotoMono-RegularItalic.ttf</file>

    </qresource>
</RCC>

我的項目文件是：

QT += quick

CONFIG += c++11

# You can make your code fail to compile if it uses deprecated APIs.
# In order to do so, uncomment the following line.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0

SOURCES += \
        main.cpp

RESOURCES += qml.qrc

# Additional import path used to resolve QML modules in Qt Creator's code model
QML_IMPORT_PATH = $$PWD/assets

# Additional import path used to resolve QML modules just for Qt Quick Designer
QML_DESIGNER_IMPORT_PATH =

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

DISTFILES +=

我的Fonts.qml文件是：

pragma Singleton
import QtQuick 2.12

Item
{  
  readonly property FontLoader robotoBold: FontLoader { source: "qrc:/Fonts/Roboto-Bold.ttf" }
  readonly property FontLoader robotoBoldItalic: FontLoader { source: "qrc:/Fonts/Roboto-BoldItalic.ttf" }
  readonly property FontLoader robotoLight: FontLoader { source: "qrc:/Fonts/Roboto-Light.ttf" }
  readonly property FontLoader robotoLightItalic: FontLoader { source: "qrc:/Fonts/Roboto-LightItalic.ttf" }
  readonly property FontLoader robotoMedium: FontLoader { source: "qrc:/Fonts/Roboto-Medium.ttf" }
  readonly property FontLoader robotoMediumItalic: FontLoader { source: "qrc:/Fonts/Roboto-MediumItalic.ttf" }
  readonly property FontLoader robotoRegular: FontLoader { source: "qrc:/Fonts/Roboto-Regular.ttf" }
  readonly property FontLoader robotoRegularItalic: FontLoader { source: "qrc:/Fonts/Roboto-RegularItalic.ttf" }

  readonly property FontLoader robotoMonoBold: FontLoader { source: "qrc:/Fonts/RobotoMono-Bold.ttf" }
  readonly property FontLoader robotoMonoBoldItalic: FontLoader { source: "qrc:/Fonts/RobotoMono-BoldItalic.ttf" }
  readonly property FontLoader robotoMonoLight: FontLoader { source: "qrc:/Fonts/RobotoMono-Light.ttf" }
  readonly property FontLoader robotoMonoLightItalic: FontLoader { source: "qrc:/Fonts/RobotoMono-LightItalic.ttf" }
  readonly property FontLoader robotoMonoMedium: FontLoader { source: "qrc:/Fonts/RobotoMono-Medium.ttf" }
  readonly property FontLoader robotoMonoMediumItalic: FontLoader { source: "qrc:/Fonts/RobotoMono-MediumItalic.ttf" }
  readonly property FontLoader robotoMonoRegular: FontLoader { source: "qrc:/Fonts/RobotoMono-Regular.ttf" }
  readonly property FontLoader robotoMonoRegularItalic: FontLoader { source: "qrc:/Fonts/RobotoMono-RegularItalic.ttf" }

  readonly property FontLoader artBrewery: FontLoader { source: "qrc:/Fonts/Art Brewery.ttf" }
}

我在 assets/fonts 文件夾中的qmldir是：

singleton Fonts 1.0 Fonts.qml

我的main.qml是

import QtQuick 2.12
import QtQuick.Window 2.12
import QtQuick.Controls 2.12

import Fonts 1.0
//import "qrc:/Fonts/"

ApplicationWindow {
  width: 640
  height: 480
  visible: true
  title: qsTr("Hello World")

  Column
  {
    spacing: 8

    anchors.fill: parent
    anchors.margins: 20

    Label // #1
    {
      text: "Pack my box with five dozen liquor jugs -- DEFAULT"
    }

//    Label // #2
//    {
//      font.family: Fonts.robotoBold.name
//      text: "Pack my box with five dozen liquor jugs -- Roboto Bold"
//    }

//    Label // #3
//    {
//      font.family: Fonts.robotoMonoRegular.name // Fonts.robotoRegular.name
//      text: "Pack my box with five dozen liquor jugs -- Roboto Mono"
//    }

//    Label // #4
//    {
//      text: "Pack my box with five dozen liquor jugs -- Art Brewery"
//      font.family: Fonts.artBrewery.name
//      font.pixelSize: 36
//    }
  }
}

Answer 1

我確信有一個更好的解決方案，但有一個方法是找到一種方法來引用 singleton 以便加載所有內容。

我將 main.qml 修改為：

  ...
  ...
  ...
  title: qsTr("Hello World")

  property var fontReference: Fonts.objectName

  Column
  ...
  ...
  ...

我不關心 fontReference 屬性。 我只需要一些方法來初始化 Fonts。 我假設在 main.cpp 中創建引擎實例后我可以調用 C++ 方法，這將完成同樣的事情，並且可能被認為是這種情況下的最佳實踐。