Thumbnails in QFileDialog

scrand

Is there an easy way to make the QFileDialog show image thumbnails? (These are for common formats, like JPG and PNG). I have googled this extensively, and I cant find a good solution. If I run my code on Windows, it uses the Windows native file dialog, which has thumbnails. But if I run it on Linux, I don't get thumbnails. There are thumbnails in the file browsers (e.g., Nemo or Dolphin), so they exist. But in the "Open File" dialog, I just get gray rectangles. Is there an easy option I'm missing that will give me thumbnails? (And if not, is there some deep design philosophy reason this basic functionality is missing from QFileDialog?)

If this isn't builtin to QFileDialog (for whatever reason), is there an easy way to write a QStyledItemDelegate that will display a thumbnail? (I have little knowledge/experience with delegates, other than I know that they exist).

Thanks!

SGaist

Hi,

Which Linux distribution is it ?
Which desktop environment ?
Are you using the distribution provided Qt ?

scrand

Currently I'm on Linux Mint with a Plasma desktop. But I see the same issue on other configurations, like Mint with Cinnamon and Fedora with Gnome. The built-in QFileDialog just seems to lack support for thumbnails.

Thanks!

SGaist

The QStyledItemDelegate road it is then.

As an educated guess, I would say that the quick way is to return the content of the image for the decoration role.

For the long run, you should check if you have a thumbnail that has been generated for the file and use that.

scrand

So I've learned a few things. One, I was using "ssh -X" into my dev account (which is on Plasma) from a Plasma workspace. I got the Qt dialog from that. But if I physically login to the dev account on Plasma, it uses the Plasma dialog, which has thumbnails. So that's something. But it looks like anything GNOME-based still doesn't work.

I think I should be able to get the path and file name from the QModelIndex. And Linux caches thumbnails in ~/.cache/thumbnails, and uses an MD5 sum of the full path and filename as the name of the thumbnail. So I should be able to figure out the correct filename for a thumbnail, and use that as my thumbnail if it exists.

So not really knowing what I'm doing, it looks like my approach is:

Subclass QStyledItemDelegate, and get the thumbnail.
Subclass QFileDialog and use the delegate.

Delegate class:

class ThumbnailDelegate : public QStyledItemDelegate
{
    Q_OBJECT
public:
    explicit ThumbnailDelegate(QObject *parent = nullptr) : QStyledItemDelegate(parent){
            QString sFile, sThumbnail;
            sFile = getFilenameFromModelIndex();
            sThumbnail = getThumbnailFilename(sFile);
            if(QFileInfo::exists(sThumbnail))
            {
                pxThumbnail = sThumbnail;
                //Make the DisplayRole use pxThumbnail
            }
    };

protected:
    QString getFilenameFromModelIndex(void); //!< Extracts the full path and filename of the file from the QModelIndex
    QString getThumbnailFilename(QString filename); //!< Computes thumbnail filename from full path.

    QPixmap pxThumbnail; //!< Pixmap of the thumbnail
};

File dialog class:

class ThumbnailFileDialog : public QFileDialog
{
    Q_OBJECT
public:
    explicit ThumbnailFileDialog(QWidget *parent = nullptr) : QFileDialog(parent){
        delegate = new ThumbnailDelegate(this);
        setItemDelegate(delegate);
    }

protected:
    ThumbnailDelegate *delegate;

};

But I can't figure out how I:

//Make the DisplayRole use pxThumbnail

Do I need to re-implement "paint()"? Or is there a simpler way to do that?

SGaist

No need for the QFileDialog subclass, just set the delegate on it.

As for your delegate, that's correct you need to implement the paint method.

What you are currently doing in the constructor is wrong. You don't have one delegate per file, it's one delegate period.