non-list-property.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-non-list-property.html
\ingroup qmllint-warnings-and-errors
 
\title Non-List Property
\brief Multiple values were assigned to a non-list property.
 
\section1 Cannot Assign Multiple Objects To A Default Non-List Property
 
\section2 What happened?
A \l{Default Properties}{default property} has multiple bindings but the default
property type is not a list type and only expects one binding.
 
\section2 Why is this bad?
All the bindings to the default property, except the last one, will be ignored. This most likely
hints that the default property should instead be a list, or that there are too many bindings to
the same property.
 
\section2 Example
 
Let's declare a component \c{MyComponent} that has one default non-list property, and then lets
bind three items to that default property:
\qml
import QtQuick
 
Item {
    component MyComponent: QtObject {
        default property Item helloWorld
    }
    MyComponent {
        // first item bound to default property:
        Item { objectName: "first" } // will warn: Cannot assign multiple objects to a default non-list property [non-list-property]
        // second item bound to default property:
        Item { objectName: "second" } // not ok: default property was bound already
        // third item bound to default property:
        Item { objectName: "third" } // not ok: default property was bound already
 
        Component.onCompleted: console.log(helloWorld.objectName) // prints "third"
    }
}
 
\endqml
You can fix this warning by replacing the default property by a list:
\qml
import QtQuick
 
Item {
    component MyComponent: QtObject {
        default property list<Item> helloWorld
    }
    MyComponent {
        // first item bound to default property:
        Item { objectName: "first" } // ok: binding a first item to the list
        // second item bound to default property:
        Item { objectName: "second" } // ok: binding a second item to the list
        // third item bound to default property:
        Item { objectName: "third" } // ok: binding a third item to the list
    }
}
\endqml
You can also fix this warning by removing all the unwanted bindings, in case the default property
is not supposed to be a list:
\qml
import QtQuick
 
Item {
    component MyComponent: QtObject {
        default property Item helloWorld
    }
    MyComponent {
        Item { objectName: "first" } // ok: just one item bound to default property
    }
    MyComponent {
        Item { objectName: "second" } // ok: just one item bound to default property
    }
    MyComponent {
        Item { objectName: "third" } // ok: just one item bound to default property
    }
}
\endqml
*/