property-override.qdoc

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// Copyright (C) 2026 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
 
/*!
\ingroup qmllint-warnings-and-errors
 
\title Property override
\brief [property-override] Wrong usage of override, final, and virtual keywords.
 
\qmllintwarningcategory property-override
 
\section1 Member does not override anything
 
\section2 What happened?
You marked a property as \c{override} without overriding anything. The base type of
the current component has no property of the same name marked as \c{virtual}.
 
\section2 Why is that bad?
The QML engine throws a runtime error when it encounters such a property.
 
\section2 Example
\qml
import QtQuick
 
Item {
    component Base: Item { virtual property int myProperty; }
    Base {
        override property int myP: 42
    }
}
\endqml
 
To fix this warning, you can:
\list
\li Remove the \c{override}-marker.
\li Double-check that the property name matches the name of a \c{virtual} or \c{override}
property in the base type of the current component.
\endlist
 
\qml
import QtQuick
 
Item {
    component Base: Item { virtual property int myProperty; }
    Base {
        property int myP: 42 // solution 1: remove override
        override property int myProperty: 42 // solution 2: fix spelling
    }
}
\endqml
 
\section1 Member shadows final member
 
\section2 What happened?
You shadowed a property which is marked as final.
 
\section2 Why is that bad?
Properties are marked as final to prevent overriding and shadowing.
The QML engine throws a runtime error when it encounters the shadowing property.
 
\section2 Example
\qml
import QtQuick
 
Item {
    component Base: Item { final property int myFinal; }
    Base {
        property int myFinal: 42
    }
}
\endqml
 
To fix this warning, you can:
\list
\li Rename the shadowing or shadowed property.
\li Replace the \c{final} marker with \c{virtual} or \c{override} and add missing \c{override}
to the overriding property.
\endlist
 
\qml
import QtQuick
 
Item {
    // solution 1: rename the property
    component Base: Item { final property int myFinal; }
    Base {
        property int myFinal2: 42
    }
 
    // solution 2: replace the final marker and add override
    component Base2: Item { virtual property int myFinal; }
    Base2 {
        override property int myFinal: 42
    }
}
\endqml
 
\section1 Member overrides final member
 
\section2 What happened?
You overrode a property which is marked as final.
 
\section2 Why is that bad?
Properties marked as \c{final} prevent overriding and shadowing.
The QML engine throws a runtime error when it encounters the overriding property.
 
\section2 Example
\qml
import QtQuick
 
Item {
    component Base: Item { final property int myFinal; }
    Base {
        override property int myFinal: 42
    }
}
\endqml
 
To fix this warning, you can:
\list
\li Rename the shadowing or shadowed property, and remove the \c{override} marker.
\li Replace the \c{final} marker with \c{virtual} from the overridden property.
\endlist
 
\qml
import QtQuick
 
Item {
    // solution 1: remove override and rename
    component Base: Item { final property int myFinal; }
    Base {
        property int myFinal2: 42
    }
 
    // solution 2: replace final marker with virtual
    component Base2: Item { virtual property int myFinal; }
    Base2 {
        override property int myFinal: 42
    }
}
\endqml
 
\section1 Member shadows member
 
\section2 What happened?
You shadowed a \c{virtual} or \c{override} property without using \c{final}
or \c{override}.
 
\section2 Why is that bad?
Properties that shadow \c{virtual} properties need a \c{override} or \c{final} marker.
The QML engine throws a runtime warning when it encounters such a property.
 
\section2 Example
\qml
import QtQuick
 
Item {
    component Base: Item { virtual property int myProperty; }
    Base {
        property int myProperty: 42
    }
}
\endqml
 
To fix this warning, make the shadowing property \c{override} or \c{final}.
 
\qml
import QtQuick
 
Item {
    component Base: Item { virtual property int myProperty; }
    Base {
        override property int myProperty: 42 // could also be final
    }
}
\endqml
 
\section1 Member overrides a non-virtual member
 
\section2 What happened?
You overrode a property that was not marked as \c{virtual} or \c{override}.
 
\section2 Why is that bad?
Properties that can be overridden need to declare it via \c{virtual} or \c{override}.
The QML engine throws a runtime error when it encounters the overridden property missing
a \c{virtual} or \c{override} marker.
 
\section2 Example
\qml
import QtQuick
 
Item {
    component Base: Item { property int myProperty; }
    Base {
        override property int myProperty: 42
    }
}
\endqml
 
To fix this warning, rename the overriding property or mark the overridden property
as \c{virtual} or \c{override}.
 
\qml
import QtQuick
 
Item {
    component Base: Item { virtual property int myProperty; }
    Base {
        override property int myProperty: 42
    }
}
\endqml
 
\section1 Property already exists in base type
 
\section2 What happened?
You shadowed a property without using as \c{virtual}, \c{override}, or \c{final}.
 
\section2 Why is that bad?
Properties that can be overridden need to declare it via \c{virtual} or \c{override}.
The QML engine warns at runtime when it encounters the shadowing property.
 
\section2 Example
\qml
import QtQuick
 
Item {
    component Base: Item { property int myProperty; }
    Base {
        property int myProperty: 42
    }
}
\endqml
 
To fix this warning, rename the shadowing or shadowed property, or add the missing
\c{virtual}, \c{override}, or \c{final} markers.
 
\qml
import QtQuick
 
Item {
    // solution 1: rename one of the properties
    component Base: Item { property int myProperty; }
    Base {
        property int myProperty2: 42
    }
 
    // solution 2: add missing markers
    component Base2: Item { virtual property int myProperty; }
    Base2 {
        final property int myProperty: 42 // could also be override
    }
}
\endqml
*/