required.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 Component is missing a required property
\brief [required] A component's required property was not bound.
 
\qmllintwarningcategory required
 
\section1 Component is missing a required property
 
\section2 What happened?
The \l{QML Object Attributes#required-properties}{required property} of a component was not set.
 
 
\section2 Why is this bad?
QML applications where components miss required properties will misbehave: they will not
start at all if a missing required property is detected statically. Dynamically created components
with missing required properties will not be created at runtime: they will be null instead.
 
\section2 Example
\qml
import QtQuick
 
Item {
    component RepeatMe: Item {
        required property int index;
        required property int helloWorld;
    }
 
    RepeatMe {} // not ok: required properties index and helloWorld not set
 
    Repeater {
        model: 10
        RepeatMe {} // not ok: required property index set by Repeater, but not helloWorld
    }
}
\endqml
To fix this warning, set the required properties:
\qml
import QtQuick
 
Item {
    component RepeatMe: Item {
        required property int index;
        required property int helloWorld;
    }
 
    RepeatMe {
        index: 0
        helloWorld: 42
    } // ok: all required properties were set
 
    Repeater {
        model: 10
        RepeatMe {
            helloWorld: index * 2 + 1
        } // ok: all required properties were set: index by the Repeater and helloWorld by the user
    }
}
\endqml
 
\sa {QML Coding Conventions#required-properties}{QML Coding Conventions - Required Properties}
*/