Looking for a way to access the source code of a QML method in C++?

Question

Looking for a way to access the source code of a QML method in C++?

I'm currently working on serializing objects to QML and I am looking for a way to retrieve the source code of functions defined within a QML object. Let's consider the following example in QML (test.qml):

import QtQml 2.2

QtObject {
    function foo() {
        return 42;
    }
}

From this, I have created a QObject: obj.

Is there any method (even if unconventional) to access the source code of the method foo within obj, without directly parsing the original QML file where obj was instantiated from?

I am open to utilizing classes like QQmlComponent that were involved in creating

obj</code, as long as no manual parsing is required. Alternatively, is there a way to extract the function's source code from the <code>test.qml

file itself without having to build a custom parser? I prefer not to make assumptions about the content or complexity of test.qml (e.g. it might differ from the example provided and may not be simplistic enough for regex or other lightweight parsers).

If we assume QML operates similarly to JavaScript, I attempted the following:

QQmlExpression expr(engine.rootContext(), obj, "foo.toString()");
QVariant sourceCode = expr.evaluate();

Unfortunately, this approach did not yield the desired results.

Edit: Referring to http://www.ecma-international.org/ecma-262/5.1/#sec-15.3.4.2, the behavior of the toString method for function objects is implementation-specific. In the case of QML, the output is as follows:

QVariant(QString, "function() { [code] }")

Given the limitations in accessing the code through JS or C++, I am now exploring possibilities beyond the public Qt API.

javascript c++qt qml qt5

Answer 1

Answer №1

Retrieving the source code of a function from an existing QML object may seem impossible at first glance. There is no apparent C++ interface or JavaScript method like toSource that can provide this information.

However, it is actually possible to retrieve the source code using the QML parser. The drawback is that the QML parser is part of the Qt private API, which means it may not be compatible with different Qt library builds.

The following snippet shows how to parse QML using the Qt 5.3.0 private API:

.pro file:

QT += qml qml-private

cpp file:

using namespace QQmlJS::AST;

class LVisitor: public QQmlJS::AST::Visitor {
public:
    LVisitor(QString code): _code(code) {}

    virtual bool visit(FunctionBody *fb) {
        qDebug() << "Visiting FunctionBody" <<
                    printable(fb->firstSourceLocation(), fb->lastSourceLocation());
        return true;
    }

private:
    QStringRef printable(const SourceLocation &start, const SourceLocation &end) {
        return QStringRef(&_code, start.offset, end.offset + end.length - start.offset);
    }

private:
    QString _code;
};

void testQmlParser() {
    QFile file(":/test.qml");
    file.open(QFile::ReadOnly);
    QString code = file.readAll();
    file.close();

    QQmlJS::Engine engine;
    QQmlJS::Lexer lexer(&engine);

    lexer.setCode(code, 1, true);

    QQmlJS::Parser parser(&engine);

    if (!parser.parse() || !parser.diagnosticMessages().isEmpty()) {
        foreach (const QQmlJS::DiagnosticMessage &m, parser.diagnosticMessages()) {
            qDebug() << "Parse" << (m.isWarning() ? "warning" : "error") << m.message;
        }
    }

    UiProgram *ast = parser.ast();

    LVisitor visitor(code);
    ast->accept(&visitor);
}

If you need more detailed information about the object where the function is defined or additional insights from the AST, you can implement further methods of QQmlJS::AST::Visitor.

Answer 2

Retrieving the source code of a function from an existing QML object may seem impossible at first glance. There is no apparent C++ interface or JavaScript method like toSource that can provide this information.

However, it is actually possible to retrieve the source code using the QML parser. The drawback is that the QML parser is part of the Qt private API, which means it may not be compatible with different Qt library builds.

The following snippet shows how to parse QML using the Qt 5.3.0 private API:

.pro file:

QT += qml qml-private

cpp file:

using namespace QQmlJS::AST;

class LVisitor: public QQmlJS::AST::Visitor {
public:
    LVisitor(QString code): _code(code) {}

    virtual bool visit(FunctionBody *fb) {
        qDebug() << "Visiting FunctionBody" <<
                    printable(fb->firstSourceLocation(), fb->lastSourceLocation());
        return true;
    }

private:
    QStringRef printable(const SourceLocation &start, const SourceLocation &end) {
        return QStringRef(&_code, start.offset, end.offset + end.length - start.offset);
    }

private:
    QString _code;
};

void testQmlParser() {
    QFile file(":/test.qml");
    file.open(QFile::ReadOnly);
    QString code = file.readAll();
    file.close();

    QQmlJS::Engine engine;
    QQmlJS::Lexer lexer(&engine);

    lexer.setCode(code, 1, true);

    QQmlJS::Parser parser(&engine);

    if (!parser.parse() || !parser.diagnosticMessages().isEmpty()) {
        foreach (const QQmlJS::DiagnosticMessage &m, parser.diagnosticMessages()) {
            qDebug() << "Parse" << (m.isWarning() ? "warning" : "error") << m.message;
        }
    }

    UiProgram *ast = parser.ast();

    LVisitor visitor(code);
    ast->accept(&visitor);
}

If you need more detailed information about the object where the function is defined or additional insights from the AST, you can implement further methods of QQmlJS::AST::Visitor.

Answer 3

Answer №2

After exploring different options, I couldn't find a straightforward way to achieve this task. However, I managed to come up with a workaround that allowed me to accomplish it.

If you're facing the same issue, I recommend checking out this resource first for insights.

As you may already know, it is possible to access a QML object in C++. To execute a function in QML, follow these steps:

Item {
    width: 100; height: 100

    Rectangle {
        property bool call:true

        objectName: "rect"
        onCallChanged()
        {
             myFunction();
        }
        function myFunction()
        {
             //your code
        }
    }
}

In your C++ code, implement the following:

QObject *rect = object->findChild<QObject*>("rect");
if (rect)
    rect->setProperty("call", !(rect->property("call").toBool()));

Here, we are utilizing the change event of the 'call' property to trigger the execution of myFunction().

Answer 4

After exploring different options, I couldn't find a straightforward way to achieve this task. However, I managed to come up with a workaround that allowed me to accomplish it.

If you're facing the same issue, I recommend checking out this resource first for insights.

As you may already know, it is possible to access a QML object in C++. To execute a function in QML, follow these steps:

Item {
    width: 100; height: 100

    Rectangle {
        property bool call:true

        objectName: "rect"
        onCallChanged()
        {
             myFunction();
        }
        function myFunction()
        {
             //your code
        }
    }
}

In your C++ code, implement the following:

QObject *rect = object->findChild<QObject*>("rect");
if (rect)
    rect->setProperty("call", !(rect->property("call").toBool()));

Here, we are utilizing the change event of the 'call' property to trigger the execution of myFunction().

Looking for a way to access the source code of a QML method in C++?

Answer №1

Answer №2

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