"Invalid property assignment:.. read-only property" in Qml
I'm attempting to use a list property in Qml for an underlying C++ object. I would like to be able to read and write it. The documentation for QQmlListProperty says that only the READ function is implemented, and is used for reading and writing the object.
QML invalid property assignment
The MapBrush class is a subclass of QObject and has Q_PROPERTY(QQmlListProperty<MapVertex> vertices READ vertices) declared as a property as per the documentation examples, and both (and more) are registered as QML types:
"Invalid property assignment: "mouseArea2" is a read-only property"
I am, in particular, confused by the fact that only mouseArea2 triggers this message - all three mouse areas seem to be closely parallel, so I'd normally expect that if any one of them had a defect, all three would have that same defect. I would guess that the problem has to be in either main.qml or Page1Form.ui.qml. Here they are: mail.qml
"Read-only property" error when using QQmlListProperty ...
You are making the overlay images are read only. @Q_PROPERTY(QQmlListProperty<OverlayImage> overlayImages READ overlayImages)@ You need to add the write function for this. Have look at how to declare Q_PROPERTY with read, write, signals etc.
QML Object Attributes
Read-only properties must be assigned a static value or a binding expression on initialization. After a read-only property is initialized, you cannot change its static value or binding expression anymore. For example, the code in the Component.onCompleted block below is invalid:
Readonly property
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 ...
Invalid property assignment: "horizontalCenter" is a read-only property
qrc:/Basic.qml:72:47: Invalid property assignment: "horizontalCenter" is a read-only property anchors.horizontalCenter: parent.horizontalCenter A minimal Qt Quick example works: import QtQuick 2.14 import QtQuick.Window 2.12 Window { width: 400 height: 400 visible: true Rectangle { anchors.fill: parent color: "transparent" border.color ...
read-only property in qml
The value never changes inside the QML. it is set once druing the opengl initialization and read in by one of the qt quick controls - slider maximumValue. When i assign value to the slider , i am getting 0. This is not correct. It seems that the Qt property system is getting initialized before the back-end opengl initialization
QT / C++ and QML Cheatsheet (with a bit of JS too)
QML Notes and Tips. Misc Tips Invalid property assignment: "___" is a read-only property. Make sure you are not accidentally using JSON style syntax with a colon. E.g., if filling in the border properties on Rectangle, it is border {}, NOT border: {} Having an element fill its parent
[Solved]Create a read only property in qml
In Qt Quick 2, you can actually declare readonly property like this: @readonly property string modelType: object.stringModel@ In this case you would not be able to modify it after creation. If you need to modify it inside Whatever.qml you could instead create an internal property and declare a public readonly alias to it.
COMMENTS
I'm attempting to use a list property in Qml for an underlying C++ object. I would like to be able to read and write it. The documentation for QQmlListProperty says that only the READ function is implemented, and is used for reading and writing the object.
The MapBrush class is a subclass of QObject and has Q_PROPERTY(QQmlListProperty<MapVertex> vertices READ vertices) declared as a property as per the documentation examples, and both (and more) are registered as QML types:
I am, in particular, confused by the fact that only mouseArea2 triggers this message - all three mouse areas seem to be closely parallel, so I'd normally expect that if any one of them had a defect, all three would have that same defect. I would guess that the problem has to be in either main.qml or Page1Form.ui.qml. Here they are: mail.qml
You are making the overlay images are read only. @Q_PROPERTY(QQmlListProperty<OverlayImage> overlayImages READ overlayImages)@ You need to add the write function for this. Have look at how to declare Q_PROPERTY with read, write, signals etc.
Read-only properties must be assigned a static value or a binding expression on initialization. After a read-only property is initialized, you cannot change its static value or binding expression anymore. For example, the code in the Component.onCompleted block below is invalid:
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 ...
qrc:/Basic.qml:72:47: Invalid property assignment: "horizontalCenter" is a read-only property anchors.horizontalCenter: parent.horizontalCenter A minimal Qt Quick example works: import QtQuick 2.14 import QtQuick.Window 2.12 Window { width: 400 height: 400 visible: true Rectangle { anchors.fill: parent color: "transparent" border.color ...
The value never changes inside the QML. it is set once druing the opengl initialization and read in by one of the qt quick controls - slider maximumValue. When i assign value to the slider , i am getting 0. This is not correct. It seems that the Qt property system is getting initialized before the back-end opengl initialization
QML Notes and Tips. Misc Tips Invalid property assignment: "___" is a read-only property. Make sure you are not accidentally using JSON style syntax with a colon. E.g., if filling in the border properties on Rectangle, it is border {}, NOT border: {} Having an element fill its parent
In Qt Quick 2, you can actually declare readonly property like this: @readonly property string modelType: object.stringModel@ In this case you would not be able to modify it after creation. If you need to modify it inside Whatever.qml you could instead create an internal property and declare a public readonly alias to it.