<![CDATA[Q_PROPERTY]]>Hello I want to use a variable from .qml file in a .cpp file. I want to do something according to value of (which is in .qml file) isCamRezistans in C++. So I want to put it's value into m_isCamRezistans. For that I use Q_PROPERTY as follows:

class CAN : public QObject
{
   Q_OBJECT

public:
   Q_PROPERTY(quint32 bitrate MEMBER m_bitrate WRITE setBitrate NOTIFY bitrateChanged)
   Q_PROPERTY(bool isCamRezistans MEMBER m_isCamRezistans READ m_isCamRezistans)

private:
   quint32 bitrate;
   bool m_isCamRezistans

Q_PROPERTY(quint32 bitrate MEMBER m_bitrate WRITE setBitrate NOTIFY bitrateChanged) does not give any errors. However, Q_PROPERTY(bool isCamRezistans MEMBER m_isCamRezistans READ m_isCamRezistans)
gives "error: expression cannot be used as a function." How can I solve that? Also do I need to use NOTIFY and signal slot mechanism in here? Or once I use Q_PROPERTY and READ, will the value be automatically updated?

]]>https://forum.qt.io/topic/126851/q_propertyRSS for NodeWed, 09 Sep 2026 16:27:26 GMTFri, 21 May 2021 06:03:24 GMT60<![CDATA[Reply to Q_PROPERTY on Fri, 21 May 2021 06:16:23 GMT]]>@Gunkut said in Q_PROPERTY:

READ m_isCamRezistans

READ requires a function not a variable, see https://doc.qt.io/qt-5/properties.html

]]>https://forum.qt.io/post/660825https://forum.qt.io/post/660825Fri, 21 May 2021 06:16:23 GMT<![CDATA[Reply to Q_PROPERTY on Fri, 21 May 2021 06:32:16 GMT]]>@jsulm I see in that case can I only use MEMBER and not NOTIFY? Would a change in qml variable directly change the member variable? Such as using:

Q_PROPERTY(QString text MEMBER m_text )

instead of :

Q_PROPERTY(QString text MEMBER m_text NOTIFY textChanged)
]]>https://forum.qt.io/post/660831https://forum.qt.io/post/660831Fri, 21 May 2021 06:32:16 GMT<![CDATA[Reply to Q_PROPERTY on Fri, 21 May 2021 06:26:15 GMT]]>@Gunkut From the documentation I linked: "A READ accessor function is required if no MEMBER variable was specified". So, you don't have to provide READ at all.

]]>https://forum.qt.io/post/660830https://forum.qt.io/post/660830Fri, 21 May 2021 06:26:15 GMT<![CDATA[Reply to Q_PROPERTY on Fri, 21 May 2021 06:24:23 GMT]]>@Gunkut

Because I will have many variables and writing a function for each of them looks inefficient

Assuming you use QtCreator:

  • Right mouse click on Q_PROPERTY
  • Select Refactor
  • Select Generate Missing Q_PROPERTY Members
]]>https://forum.qt.io/post/660829https://forum.qt.io/post/660829Fri, 21 May 2021 06:24:23 GMT<![CDATA[Reply to Q_PROPERTY on Fri, 21 May 2021 06:20:09 GMT]]>Okay so is there an easier way to get values of qml variables. Because I will have many variables and writing a function for each of them looks inefficient.

]]>https://forum.qt.io/post/660826https://forum.qt.io/post/660826Fri, 21 May 2021 06:20:09 GMT<![CDATA[Reply to Q_PROPERTY on Fri, 21 May 2021 06:16:23 GMT]]>@Gunkut said in Q_PROPERTY:

READ m_isCamRezistans

READ requires a function not a variable, see https://doc.qt.io/qt-5/properties.html

]]>https://forum.qt.io/post/660825https://forum.qt.io/post/660825Fri, 21 May 2021 06:16:23 GMT