- Qt 6.9
- Qt Qml
- QML Lint Warning and Errors
- Readonly property
- Qt 6.9.1 Reference Documentation

# Readonly property

This warning category is spelled `[read-only-property]` by qmllint.

## Cannot assign to read-only property

### What happened?

A read-only property was written.

### Why is this bad?

The QML engine will throw a Type Error when it sees the write to a read-only property.

### Example

     import QtQuick

     Item {
         id: root
         readonly property int someNumber: 10

         Component.onCompleted: {
             someNumber = 20  // not ok: TypeError: Cannot assign to read-only property
         }
     }

To fix this warning, remove the write to the read-only property, write to another non-read-only property, or remove the readonly modifier if you are the author of the property definition.

See also Read-Only Properties.