String passing from JavaScript to Qt/C++ object

Question

I'm stuck on a QtWebKit bridge issue on Windows and I ran out of options. I don't have access to the exact code used but its something like below.

C++

class MyObject : QWidget {
    Q_OBJECT

public:
    QString data() const;
    void setData(QString);
    Q_PROPERTY(QString data READ data WRITE setData)
};
/* ... */
MyObject myObject;
frame->addToJavaScriptWindowObject("myObject", &myObject);

JavaScript

function drop(e) {
    var url = e.dataTransfer.getData('url');
    //alert(url);   // Displays url correctly
    myObject.data = url;    // Assigns url to C++ object myObject
}

The alert box correctly displays the string value, e.g. 10.10.0.1. The parameter on setData gives me the string "1". If I then view then memory at that address, I see the full url in memory (formatted as UTF-32 (4 bytes per character)), but whatever I try (toStdString, toAscii, utf16 - just to get sensible data) I do not seem to be able to get/use the whole string.

I event thought that maybe the debugger is playing a trick on me, so I pass the data to the method that actually needs this data (which also used a QString) it all might work - but sadly no.

Even if I make MyObject::setData Q_INVOKABLE and call setData directly I get the same behaviour:

myObject.setData(url);  // Assigns url to C++ object myObject

If I just pass the data as literal, all DOES work correctly, like

myObject.setData('10.10.0.1');

or

myObject.data = '10.10.0.1';

I do not understand why passing a literal works but a variable not, the 'url' variable should be a string type.

score 0 · Accepted Answer · edited May 23 '17 at 11:47

I'm partly there. String passing works as expected. However, the C++ object is embedded on a webpage and wraps an ActiveX (ActiveQt) object. For this, I've seen some pages where you create a class that inherits from a QWebPage. There you have a createPlugins method that asks the QUiLoader to construct the widget for you (alternatively you use the Qt Metatype system). And my C++ object is registered. When I use this custom WebPage on my WebView (using setPage), the strings are passed in wrongly. When I disable calling setPage, the strings passed correctly.

So string passing works (in some conditions).

I've created a new issue for this: Qt Webkit bridge ActiveQt string

String passing from JavaScript to Qt/C++ object

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