incompatible-type.qdoc

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// Copyright (C) 2023 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
 
/*!
\page qmllint-warnings-and-errors-incompatible-type.html
\ingroup qmllint-warnings-and-errors
 
\title Incompatible type
\brief [incompatible-type] An object, value, or expression is used on an incompatible type.
 
\qmllintwarningcategory incompatible-type
 
\section1 Cannot assign to default property of incompatible type
 
\section2 What happened?
You assigned an object to a
\l{qtqml-syntax-objectattributes.html#default-properties}{default property}
of an incompatible type.
 
\section2 Why is this bad?
The QML engine will not be able to assign the object at runtime.
 
\section2 Example
\qml
import QtQuick
 
Item {
    component MyType: QtObject {
        default property list<Item> myDefaultProperty
    }
 
    MyType {
        QtObject {} // note: QtObject does not inherit from Item
    }
}
 
\endqml
To fix this warning, bind a compatible type to the property or, if
you are the author of the default property, change the type in
the definition:
\qml
import QtQuick
 
Item {
    component MyType: QtObject {
        default property list<Item> myDefaultProperty
    }
 
    MyType {
        Item {}
    }
 
    component AlternativeMyType: QtObject {
        default property list<QtObject> myDefaultProperty
    }
 
    AlternativeMyType {
        QtObject {} // is ok for AlternativeMyType
    }
}
 
\endqml
 
\section1 On-binding for property has wrong type
 
\section2 What happened?
You used an invalid
\l{qtqml-cppintegration-definetypes.html#property-modifier-types}{property modifier type}.
 
\section2 Why is this bad?
The QML engine will not be able to use the property modifier type at runtime.
 
\section2 Example
\qml
import QtQuick
 
Item {
    property int xxx
    Item on xxx { ... }
}
 
\endqml
To fix this warning, remove the \c on or use a valid
\l{qtqml-cppintegration-definetypes.html#property-modifier-types}{property modifier type}:
\qml
import QtQuick
 
Item {
    property int xxx
    Item { ... }
 
    // Alternative: use a valid property modifier type
    NumberAnimation on xxx { ... }
}
 
\endqml
 
\section1 Construction from string is deprecated; Use structured value type construction instead
 
\section2 What happened?
You constructed a QML_STRUCTURED_VALUE using a string.
 
\section2 Why is this bad?
This is deprecated and prone to typos.
 
\section2 Example
\qml
import QtQuick
 
Item {
    property point p: "5, 6"
}
 
\endqml
To fix this warning, populate the structured value type as explained in the
QML_STRUCTURED_VALUE description instead of binding a string to the property:
 
\qml
import QtQuick
 
Item {
    property point p: ({ x: 5, y: 6 })
}
 
\endqml
 
\section1 Function without return type annotation returns
 
\section2 What happened?
You returned a value from a function without return type annotation.
 
\section2 Why is this bad?
You annotated the function to not return anything so the function should not return anything.
The QML tooling will not be able to process the method and the QML engine will ignore the
returned value in a future Qt version.
 
\section2 Example
\qml
import QtQuick
 
Item {
    function f(x: int) {
        ...
        return x
    }
}
 
\endqml
To fix this warning, adapt the function signature to the new return type or remove the return value:
\qml
import QtQuick
 
Item {
    function f(x: int): int {
        ...
        return x
    }
    function alternativeF(x: int) {
        ...
        return
    }
}
 
\endqml
 
\section1 Cannot assign binding/object/literal
 
\section2 What happened?
You bound an object, literal, or expression to a property of an incompatible type.
 
\section2 Why is this bad?
The QML engine will not be able to assign the object, literal, or expression at runtime.
 
\section2 Example
\qml
import QtQuick
 
Item {
    property date xxx: 42
}
 
\endqml
To fix this warning, bind an object, value, or expression of a compatible type:
\qml
import QtQuick
 
Item {
    property date xxx: new Date()
}
 
\endqml
 
*/