QML: List all object members/properties in console

Question

Is there any way to list all object members/properties in QML & Qt 5.1?

Such as:

var obj=myQObject;
console.log(obj)
// expected output:
// obj { x:123..... }

This would be very helpful for debugging.

Answer 1

Straight javascript offers what you are looking for:

JSON.stringify(anything)

It works on QML items such as Rectangle, and it also works on most arbitrary objects!

Converting an object to a string

Answer 2

With meta objects you can debug all properties of any QML obj (i.e. QQuickItem).

You need some C++ to get the meta object of a QML component and get back property names and values as text in QML.

First you create a QMLDebugger class in C++ with a properties method:

QString QMLDebugger::properties(QQuickItem *item, bool linebreak)
{
    const QMetaObject *meta = item->metaObject();

    QHash<QString, QVariant> list;
    for (int i = 0; i < meta->propertyCount(); i++)
    {
        QMetaProperty property = meta->property(i);
        const char* name = property.name();
        QVariant value = item->property(name);
        list[name] = value;
    }

    QString out;
    QHashIterator<QString, QVariant> i(list);
    while (i.hasNext()) {
        i.next();
        if (!out.isEmpty())
        {
            out += ", ";
            if (linebreak) out += "\n";
        }
        out.append(i.key());
        out.append(": ");
        out.append(i.value().toString());
    }
    return out;
}

This function can be static or instanceiable, doesn't matter. QML does not support exporting static methods from C++ to QML anyway. I use the header:

public:
    Q_INVOKABLE static QString properties(QQuickItem *item, bool linebreak = true);

Now you export the class to QML. In you main.cpp add

#include "qmldebugger.h"

and

qmlRegisterType<QMLDebugger>("MyDemoLibrary", 1, 0, "QMLDebugger");

In your QML file import you new library, create an instance of QMLDebugger and start happy debugging:

import QtQuick 2.0
import MyDemoLibrary 1.0

Rectangle {
    id: mainRectangle
    width: 360
    height: 360
    color: "silver"

    Text {
        id: textElement
        color: "#d71f1f"
        text: qsTr("Hello World")
        font.bold: true
        font.italic: true
        font.underline: true
        style: Text.Raised
        horizontalAlignment: Text.AlignHCenter
        font.pointSize: 16
        anchors.top: parent.top
        anchors.left: parent.left
        anchors.right: parent.right
    }

    QMLDebugger {
        id: qmlDebugger
    }

    Component.onCompleted: {
        console.log("Debug mainRectangle:");
        console.log(qmlDebugger.properties(mainRectangle));
        console.log("Debug textElement:");
        console.log(qmlDebugger.properties(textElement, false));
    }
}

The full source code is available as a minimal Qt Creator project on: https://github.com/webmaster128/QMLDebugger

Answer 3

Just convert the QML/C++ component/object into JavaScript var object, and use the for-each syntax to list all the property:

function listProperty(item)
{
    for (var p in item)
    console.log(p + ": " + item[p]);
}

in your QML file, just call

onClicked:
{
    listProperty(ItemID)

    //or with this to list self properties
    listProperty(this)
}

Answer 4

in case of any one wants to list only properties of an object, no signals nor slots you can use this

function listProperty(item)
{
    for (var p in item)
    {
        if( typeof item[p] != "function" )
            if(p != "objectName")
                console.log(p + ":" + item[p]);
    }

}

Answer 5

If you are not only interested in console-debugging, there is a program called GammaRay by KDAB (link) that lets you introspect and change all properties during the runtime of a QWidgets or QtQuick based program. Pretty neat!

Answer 6

I did not see a solution to iterate all properties yet. But maybe this helps you as a first step.

For every Quick Item you can print out the properties of Item:

import QtQuick 2.0

Rectangle {
    width: 360
    height: 360

    function debugQuickItem(object) {
        var properties = {
            'activeFocus': object.activeFocus,
            'activeFocusOnTab': object.activeFocusOnTab,
            'anchors.alignWhenCentered': object.anchors.alignWhenCentered,
            'anchors.baseline': object.anchors.baseline,
            'anchors.baselineOffset': object.anchors.baselineOffset,
            'anchors.bottom': object.anchors.bottom,
            'anchors.bottomMargin': object.anchors.bottomMargin,
            'anchors.centerIn': object.anchors.centerIn,
            'anchors.fill': object.anchors.fill,
            'anchors.horizontalCenter': object.anchors.horizontalCenter,
            'anchors.horizontalCenterOffset': object.anchors.horizontalCenterOffset,
            'anchors.left': object.anchors.left,
            'anchors.leftMargin': object.anchors.leftMargin,
            'anchors.margins': object.anchors.margins,
            'anchors.right': object.anchors.right,
            'anchors.rightMargin': object.anchors.rightMargin,
            'anchors.top': object.anchors.top,
            'anchors.topMargin': object.anchors.topMargin,
            'anchors.verticalCenter': object.anchors.verticalCenter,
            'anchors.verticalCenterOffset': object.anchors.verticalCenterOffset,
            'antialiasing': object.antialiasing,
            'baselineOffset': object.baselineOffset,
            'children': object.children,
            'childrenRect.height': object.childrenRect.height,
            'childrenRect.width': object.childrenRect.width,
            'childrenRect.x': object.childrenRect.x,
            'childrenRect.y': object.childrenRect.y,
            'clip': object.clip,
            'data': object.data,
            'enabled': object.enabled,
            'focus': object.focus,
            'height': object.height,
            'implicitHeight': object.implicitHeight,
            'implicitWidth': object.implicitWidth,
            'layer.effect': object.layer.effect,
            'layer.enabled': object.layer.enabled,
            'layer.format': object.layer.format,
            'layer.mipmap': object.layer.mipmap,
            'layer.samplerName': object.layer.samplerName,
            'layer.smooth': object.layer.smooth,
            'layer.sourceRect': object.layer.sourceRect,
            'layer.textureSize': object.layer.textureSize,
            'layer.wrapMode': object.layer.wrapMode,
            'opacity': object.opacity,
            'parent': object.parent,
            'resources': object.resources,
            'rotation': object.rotation,
            'scale': object.scale,
            'smooth': object.smooth,
            'state': object.state,
            'states': object.states,
            'transform': object.transform,
            'transformOrigin': object.transformOrigin,
            'transitions': object.transitions,
            'visible': object.visible,
            'visibleChildren': object.visibleChildren,
            'width': object.width,
            'x': object.x,
            'y': object.y,
            'z': object.z,
        }
        var out = "{ "
        for (var key in properties)
        {
            out += "'" + key + "': " + properties[key] + ", "
        }
        out += "}"
        return out;
    }

    Text {
        id: textObject
        anchors.centerIn: parent
        text: "Hello World"
    }

    Component.onCompleted: console.log(debugQuickItem(textObject));
}

Output:

{ 'activeFocus': false, 'activeFocusOnTab': false, 'anchors.alignWhenCentered': true, 'anchors.baseline': QVariant(QQuickAnchorLine), 'anchors.baselineOffset': 0, 'anchors.bottom': QVariant(QQuickAnchorLine), 'anchors.bottomMargin': 0, 'anchors.centerIn': QQuickRectangle_QML_0(0x29857d0), 'anchors.fill': null, 'anchors.horizontalCenter': QVariant(QQuickAnchorLine), 'anchors.horizontalCenterOffset': 0, 'anchors.left': QVariant(QQuickAnchorLine), 'anchors.leftMargin': 0, 'anchors.margins': 0, 'anchors.right': QVariant(QQuickAnchorLine), 'anchors.rightMargin': 0, 'anchors.top': QVariant(QQuickAnchorLine), 'anchors.topMargin': 0, 'anchors.verticalCenter': QVariant(QQuickAnchorLine), 'anchors.verticalCenterOffset': 0, 'antialiasing': false, 'baselineOffset': 14, 'children': [object Object], 'childrenRect.height': 0, 'childrenRect.width': 0, 'childrenRect.x': 0, 'childrenRect.y': 0, 'clip': false, 'data': [object Object], 'enabled': true, 'focus': false, 'height': 17, 'implicitHeight': 17, 'implicitWidth': 80.5625, 'layer.effect': null, 'layer.enabled': false, 'layer.format': 6408, 'layer.mipmap': false, 'layer.samplerName': source, 'layer.smooth': false, 'layer.sourceRect': QRectF(0, 0, 0, 0), 'layer.textureSize': QSize(-1, -1), 'layer.wrapMode': 0, 'opacity': 1, 'parent': QQuickRectangle_QML_0(0x29857d0), 'resources': [object Object], 'rotation': 0, 'scale': 1, 'smooth': true, 'state': , 'states': [object Object], 'transform': [object Object], 'transformOrigin': 4, 'transitions': [object Object], 'visible': true, 'visibleChildren': [object Object], 'width': 80.5625, 'x': 139.71875, 'y': 171, 'z': 0, }