QMLからQt付属の標準アイコンを使う方法

@Violet-Giraffe
you can simply create your custom QQuickImageProvider to do so
Map the names to the QStyle::StandardPixmap enum and convert the QIcon to a QPixmap/QImage.

QT += quick widgets
CONFIG += c++11

DEFINES += QT_DEPRECATED_WARNINGS

SOURCES += main.cpp

RESOURCES += qml.qrc

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

# 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

#include <QGuiApplication>
#include <QQmlApplicationEngine>

#include <QQuickImageProvider>
#include <QCommonStyle>

class StandardPixmapProvider : public QQuickImageProvider
{
public:
    StandardPixmapProvider()
        : QQuickImageProvider(QQuickImageProvider::Pixmap)
    {
    }

    QPixmap requestPixmap(const QString &id, QSize *size, const QSize &requestedSize)
    {
        std::map<QString, QStyle::StandardPixmap> iconMap = {
            {"DialogOpenButton", QStyle::SP_DialogOpenButton},
            {"DialogSaveButton", QStyle::SP_DialogSaveButton},
        };

        auto icon = QCommonStyle().standardPixmap(iconMap[id]);
        *size = icon.size();  // original image size

        if      (requestedSize.isValid()   ) icon = icon.scaled(requestedSize);
        else if (requestedSize.width()  > 0) icon = icon.scaledToWidth(requestedSize.width());
        else if (requestedSize.height() > 0) icon = icon.scaledToHeight(requestedSize.height());

        return icon;
    }
};


int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);
    QQmlApplicationEngine engine;

    engine.addImageProvider(QLatin1String("standard"), new StandardPixmapProvider);

    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
    if (engine.rootObjects().isEmpty())
        return -1;

    return app.exec();
}

import QtQuick 2.9
import QtQuick.Controls 1.5
import QtQuick.Dialogs 1.2
import QtQuick.Layouts 1.3

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

    Action {
        id: open
        text: "&Open"
        shortcut: StandardKey.Open
        iconSource: "image://standard/DialogOpenButton"
    }
    Action {
        id: save
        text: "&Save"
        shortcut: StandardKey.Save        
        iconSource: "image://standard/DialogSaveButton"
    }

    toolBar: ToolBar{
        RowLayout {
            ToolButton { action: open }
            ToolButton { action: save }
        }
    }

    menuBar: MenuBar {
        Menu { title: qsTr("&File") }
        Menu { title: qsTr("&Edit") }
        Menu { title: qsTr("&Help") }
    }

    TextEdit {
        id: textEdit
        focus: true
    }
}