Edit: Please make sure to look into the comments. While this is a rather old post, thankfully, still constructive comments are raised that point out important aspects. Unfortunately, my time does not permit to properly update the post nor did it permit me to play with Qt/QML for quite some time. So, I just refer to the comments below. Thanks a lot to the commenters.

The following snippets show how one can easily interact with the clipboard from QML code with the help of a tiny C++ wrapper / adapter. This code should work for all QML versions.

The C++ code is very simple and straight forward:

#ifndef QMLCLIPBOARDADAPTER_H
#define QMLCLIPBOARDADAPTER_H

#include <QApplication>
#include <QClipboard>
#include <QObject>

class QmlClipboardAdapter : public QObject
{
    Q_OBJECT
public:
    explicit QmlClipboardAdapter(QObject *parent = 0) : QObject(parent) {
        clipboard = QApplication::clipboard();
    }

    Q_INVOKABLE void setText(QString text){
        clipboard->setText(text, QClipboard::Clipboard);
        clipboard->setText(text, QClipboard::Selection);
    }

private:
    QClipboard *clipboard;
};

#endif // QMLCLIPBOARDADAPTER_H

Registration of our adapter is done as usual in the main.cpp file:

#include <QtDeclarative>
...
#include "qmlclipboardadapter.h"

Q_DECL_EXPORT int main(int argc, char *argv[])
{
    ...
    qmlRegisterType("meepasswords", 1, 0, "QClipboard");
    ...
}

And finally the clipboard can be used from QML code:

...
import meepasswords 1.0
...
    QClipboard{
        id: clipboard
    }
...
    onAccepted: clipboard.setText("foo")
...

Note that this implementation is a write-only clipboard. Though, modifying the above code to enable a read-write clipboard is straight forward.