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How to save the image in clipboard in variable and restore it to clipboard later?



  • I connect a slot to the dataChanged signal of QClipboard to store the image in the clipboard to a variable mimedata(reference):

    void MyWin::clipboardDataChanged()
    {
        const QMimeData * m=QApplication::clipboard()->mimeData();
        mimedata = new QMimeData();
        
        foreach(QString format, m->formats())
        {
            QByteArray data = m->data(format);
            if(format.startsWith("application/x-qt"))
            {
                int index1 = format.indexOf('"') + 1;
                int index2 = format.indexOf('"', index1);
                format = format.mid(index1, index2 - index1);
            }
            mimedata->setData(format, data);
        }
    }
    

    And restore mimedata to clipboard as follows:

    void MyWin::onrestore()
    {
         QApplication::clipboard()->setMimeData(mimedata);
    }
    

    However, the data set to the clipboard seems corrupted. If I paste from the clipboard to Paint, it says "The information on the Clipboard can't be inserted into Paint." I printed the format of the data in the clipboard, i.e., "application/x-qt-image". So I think it is not a format that is supported by other applications. Is this a bug of Qt?


  • Qt Champions 2019

    Why do you modify the format? What do you try to achieve in the first place?



  • I just use the code in the reference link which is said the correct way to copy mime data. But that does not matter, even if I do not modify the format, the result is the same.


  • Qt Champions 2019

    Is still don't see a point on what you're trying to do - do you want to put something into the clipboard ord do you want to read from? Currently you read data from the clipboard, modify it in a strange way and later set it back - what's the reason for this?



  • I just want to save the clipboard, then restore it later in case its content is changed.


  • Qt Champions 2019

    Then don't modify the mime-data and simply copy it over.



  • Simply copying it over does not help. I think qt should return the format like application/x-qt-image;value="image/bmp", so my code will change the format to "image/bmp" before setting it back to clipboard. But it only returns "application/x-qt-image", which is not a standard mime type, and my code does not change the format actually. I'm on Windows. Don't know if it is the case on Linux. I think it should be bug of Qt.


  • Qt Champions 2019

    application/x-qt-image is only a qt-internal format, when you iterate over the available formats you will also find the others - there is absolutely no need to modify them and I still don't understand why you want to restore the clipboard.



  • "application/x-qt-image" is the only format when I press the Print-Screen key to take a screenshot. This problem seems related to the bug:https://bugreports.qt.io/browse/QTBUG-4110. Qt Experts, can you confirm it?



  • You can use auto image = qvariant_cast<QImage>(m->imageData()); to get a QImage from an application/x-qt-image mime and you can do whatever you want with that.
    For example you can use:

    QByteArray imageData;
    QBuffer imageBuffer(&imageData);
    imageBuffer.open(QIODevice::WriteOnly);
    if(image->save(&imageBuffer,"PNG")){
        mime = new QMimeData;
        mime->setData(QStringLiteral("image/png"),imageData);
        QApplication::clipboard()->setMimeData(mime);
    }
    


  • I've tried your code, unfortunately, it does not work. After I press the Print-Screen key and go to MS Paint, the "Paste“ button is enabled, which means there is something in the clipboard that can be pasted. After I run your code and go to Paint again, the "Paste" button is disabled. So the data in clipboard is corrupted.



  • Actually, it's much easier than I was thinking, you can load images in the clipboard just by using QApplication::clipboard()->setPixmap or QApplication::clipboard()->setImage.
    For example:

    #include <QApplication>
    #include <QPushButton>
    #include <QClipboard>
    #include <QPixmap>
    int main(int argc, char *argv[])
    {
        QApplication app(argc,argv);
        QPushButton quitButton(QStringLiteral("SaveImage"));
        QObject::connect(&quitButton,&QPushButton::clicked,[&quitButton](){
            QApplication::clipboard()->setPixmap(quitButton.grab());
        });
        quitButton.show();
        return app.exec();
    }
    


  • Yes, it has no problem to set a QImage or QPixmap to clipboard. But it has problem getting the image from clipboard and setting it back to clipboard. And I want to restore every component in the clipboard not just image, which means I must copy the mimedata.



  • @yetanotherqtfan said in How to save the image in clipboard in variable and restore it to clipboard later?:

    And I want to restore every component in the clipboard not just image

    "application/x-qt-image" is the only format when I press the Print-Screen key to take a screenshot.

    I don't think I follow



  • For the print-screen case, there is only one format "application/x-qt-image". But in most cases,e.g., copying images and text in a word document, there would be more components in the clipboard. In the print-screen case, you can copy the clipboard image to a QImage object then set it to clipboard later. But for other cases, you may get a null image. Even you get a valid QImage, setting it back to clipboard will destroy other components in it. So the general method would be copying the mimedata object, and this would fail even for the print-screen case.



  • Something like this?

    bool skipOne = false;
        QObject::connect(app.clipboard(),&QClipboard::dataChanged,[&skipOne](){
            if(skipOne){
                skipOne=false;
                return;
            }
            const QMimeData* mime = QApplication::clipboard()->mimeData();
            const QStringList formats = mime->formats();
            const int imageIdx = formats.indexOf(QLatin1String("application/x-qt-image"));
            if(imageIdx<0)
                return;
            const QImage image = qvariant_cast<QImage>(mime->imageData());
            if(image.isNull())
                return;
            QMimeData* adjMime = new QMimeData;
            adjMime->setImageData(image);
            for(int i=0;i<formats.size();++i){
                if(i==imageIdx)
                    continue;
                adjMime->setData(formats.at(i),mime->data(formats.at(i)));
            }
            skipOne=true;
            QApplication::clipboard()->setMimeData(adjMime);
        });
    


  • @VRonin said in How to save the image in clipboard in variable and restore it to clipboard later?:

    dat

    I will try your latest code. But all my attempts in setting the QMimeData failed.


  • Qt Champions 2019

    @VRonin said in How to save the image in clipboard in variable and restore it to clipboard later?:

    "application/x-qt-image" is the only format when I press the Print-Screen key to take a screenshot.

    I don't think I follow

    The problem is that @yetanotherqtfan does not understand that this is the one and only format you will get from Qt since when the data is retrieved from the native clipboard and there is image data it will be converted to this internal mime-format. And the other way round so there is absolutely no need to replace the mime-type (it's even counter-productive - see https://code.woboq.org/qt5/qtbase/src/plugins/platforms/windows/qwindowsmime.cpp.html#1140 )



  • @Christian-Ehrlicher I have one question. I tried to save the transparent image to clipboard but it's not working on windows but on ubuntu. I am not sure why. When I used setImage or setPixmap, the image was always opaque even it has transparency. How can I fix this?


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