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

Unsolved Cpp to JS: function with struct as parameter