uncreatable-type.qdoc

Go to the documentation of this file.

// Copyright (C) 2023 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
 
/*!
\ingroup qmllint-warnings-and-errors
 
\title Uncreatable type
\brief [uncreatable-type] Types that can't be created.
 
\qmllintwarningcategory uncreatable-type
 
\section1 Namespace must start with an upper case letter
 
\section2 What happened?
You used a QML object from a lower-case namespace.
 
\section2 Why is this bad?
The QML language forbids lower-case namespaces.
 
\section2 Example
\qml
import QtQuick as quick
 
quick.Item { ... }
 
\endqml
To fix the warning, rename the namespace to start with a capital letter:
\qml
import QtQuick as Quick
 
Quick.Item { ... }
 
\endqml
 
\section1 Singleton type is not creatable
 
\section2 What happened?
You tried to instantiate a QML object from a \l{qml-singleton.html}{singleton type}.
 
\section2 Why is this bad?
The QML language forbids instantiations of singletons.
 
\section2 Example
\qml
import QtQuick
 
Item {
    Qt { // note: Qt is a singleton type
        id: qt
    }
 
    property string someProperty: qt.uiLanguage
}
 
\endqml
To fix the warning, use the singleton directly without instantiating it:
\qml
import QtQuick
 
Item {
    property string someProperty: Qt.uiLanguage
}
 
\endqml
 
\section1 Type is not creatable
 
\section2 What happened?
You tried to instantiate a QML object from an
\l{QML_UNCREATABLE}{uncreatable type}.
 
\section2 Why is this bad?
Uncreatable types are specifically marked to forbid instantiations.
You might be misusing a type that should only be used as an attached type or
as an interface.
 
\section2 Example
 
\section3 Attached type misuse
\qml
import QtQuick
 
Item {
    Keys {
        onPressed: function (key) { ... }
    }
}
 
\endqml
To fix the warning, use the \c Keys attached type instead of instantiating it:
\qml
import QtQuick
 
Item {
    Keys.onPressed: function (key) { ... }
}
 
\endqml
 
\section3 Interface misuse
\qml
import QtQuick
 
Item {
    property PointerHandler myHandler: PointerHandler {}
}
 
\endqml
To fix the warning, use a more specific derived type like \c TapHandler:
\qml
import QtQuick
 
Item {
    property PointerHandler myHandler: TapHandler {}
}
 
\endqml
 
*/