Cpp to JS: function with struct as parameter

[Slei]

Hey,

I'm currentlry trying to emit an js function on cpp

js: testTextMessage(msg: TextMessage)

c++:

.h

struct TextMessage
{
  int sentTime;
  QString messageText;
};

Q_DECLARE_METATYPE(TextMessage)

 Q_INVOKABLE void testTextMessage(TextMessage msg);

.cpp
in an Widget Ctor where the QWebEngine is created:

qRegisterMetaType<TextMessage>("TextMessage");

Call:

TextMessage msg;
msg.messageText = "Frohen Joghurt mit Bier";
msg.sentTime = 13374;

emit testTextMessage(msg);

But i get following error when emitting:

"Uncaught TypeError: Cannot read property 'messageText' of null", source: qrc:///web/index.html (929)

can anyone help?

[JonB]

@Slei
Not my area quite so excuse if dumb question, but are we supposed to see the implementation code for your testTextMessage(TextMessage msg), because somewhere your msg is null?

[Slei]

the implementation of this function is JS side and it only creates and console output with the struct data

[Slei]

I still haven't really found any solution to this.
Has anyone any idea what might be the issue here?

[kkoehne]

Where do you execute your JS? As part of a QWebEnginePage , as the category 'QtWebEngine' hints at?

If so, the direct export of types with qRegisterMetaType doesn't work. Web pages are rendered in a separate process, isolated from the rest of your program. You need something like QWebChannel to communicate back and forth ...

[Slei]

@kkoehne said in Cpp to JS: function with struct as parameter:

You need something like QWebChannel to communicate back and forth ...

I think I already work with QWebEngine. Communitcating with simple parameters works fine(Q Types and built in types)
But I'm not fully sure how I can support user-defined types.

[kkoehne]

@Slei , can you post some complete example code?

THere's no direct way to expose a C++ type to JS inside a QWebEnginePage - you'd need to recreate the type yourself using JS.

If you however want to expose your type in QML/JS, see http://doc.qt.io/qt-5/qtqml-cppintegration-definetypes.html for a full overview of the various types.

[Slei]

// the webengine view widget
m_wev = new QWebEngineView(this);
QWebChannel* channel = new QWebChannel(m_wev);

channel->registerObject(QString("ChatWidget"), this);
m_wev->page()->setWebChannel(channel);


m_wev->load(QUrl("qrc:///web/index.html"));
m_wev->show();

is the way I'm creating the webcontent widget

and the rest is as written in my initial post.

I just want to send a struct to the Js from c++.
It does work with a QList<QString>, QString etc.

I think the other obvious solution might be using json and creating it myself, but i just wanna know if Qt might serialize it itself when I register my struct/class correctly

[Slei]

Here they suggest to use qRegisterMetaType:

https://stackoverflow.com/questions/34818557/how-to-register-a-class-for-use-it-in-a-qwebchannel-signal-in-qt

Which seems not to work for me

[Slei]

but i've also found the following issue:

https://bugreports.qt.io/browse/QTBUG-61515

[Slei]

Ok my solution to this:

I manually create a QJsonObject for my custom type and send it as parameter, on the js everything stayed the same since js already deserializes the data