Attached property VS Q_EXTENDED: add custom properties to a general QML Control Item

[nico88desmo]

Dear all,

I'm looking for add properties to a generic QML Control Item

Supposing I have a class similar to this one:

class ExtraProperties : public QObject {
    Q_OBJECT

public:
    Q_PROPERTY(QString placeholderText READ getPlaceholderText WRITE setPlaceholderText NOTIFY placeholderTextChanged)
    Q_PROPERTY(QString helperText READ getHelperText WRITE setHelperText NOTIFY helperTextChanged)

private:
    QString placeholderText;
    QString helperText;

public:
    explicit ExtraProperties(QObject* parent = nullptr);

    QString getPlaceholderText() const;
    void setPlaceholderText(const QString& newPlaceholderText);

    QString getHelperText() const;
    void setHelperText(const QString& newHelperText);

signals:
    void placeholderTextChanged();
    void helperTextChanged();
};

I'd like to adding these two properties (placeholderText and helperText) to some QML components such as:

• TextEdit
• SpinBox
• ecc..

In Qt docs, I see there are mainly two possibilities to reach this target:

1. using Q_EXTEND
   This is the solution I'd prefer, however this isn't feasible because I haven't access to QQuickTextEdit headers, because they are private; so this code couldn't work (following this example)

   struct QLineEditForeign {
      Q_GADGET
      QML_FOREIGN(QQuickTextEdit) <--- KO, no headers to QuickTextEdit
      QML_NAMED_ELEMENT(TextEdit)
      QML_EXTENDED(ExtraProperties)
   };

2. using attached-properties
   The problem of attaching properties is that I'm not able to use them outside of item, for example:

   class ExtraPropertiesAtt : public QObject {
      Q_OBJECT
      QML_ATTACHED(ExtraProperties)
      QML_ELEMENT
   public:
      static ExtraProperties* qmlAttachedProperties(QObject *object) {
         return new ExtraProperties(object);
      }
   };

From QML then

• CustomItem.qml

Item {
   ...
   ExtraPropertiesAtt.placeholderText: "Sample"
   ...
}

• Main.qml

import CustomItem

Window {
   CustomItem {
      ExtraPropertiesAtt.placeholderText: "Test" <--- KO
   }
}

So, are there any other ways to achieve this goal?

Thanks,
Nicola

[GrecKo]

@nico88desmo How does the "KO" occur in your last snippet?

[nico88desmo]

@GrecKo from my first test code, it seems that CustomItem's placeholderText value is set equals to Item's placeholderText, ignoring the assignment in Main.qml.

That's why I wrote KO; it's quite strange... unless I'm doing some other errors in other code parts.

[nico88desmo]

@nico88desmo said in Attached property VS Q_EXTENDED: add custom properties to a general QML Control Item:

@GrecKo from my first test code, it seems that CustomItem's placeholderText value is set equals to Item's placeholderText, ignoring the assignment in Main.qml.

That's why I wrote KO; it's quite strange... unless I'm doing some other errors in other code parts.

@GrecKo I've rechecked the code, and effectively the problem was that in my real code (I've posted just a snippet in order to no put boilerplate code inside forum page), Item is inside a plugin and Main.qml is in the main application.

The problem was quite stupid: plugin wasn't recompiled so Main.qml uses an old Item's version.

Now attached property works as expected