[Qt5] Set Default Suffix

[Salads]

I made a small program that saves a file, but people who use Ubuntu say that they can't properly save the file without manually putting a file extension in the save file name. I tried using the setDefaultSuffix function though I don't see how it would fit with the getSaveFileName function that I'm using.

Here's my code for the save button:

void MainWindow::on_save_clicked()
{
    if (pngData.isEmpty())
    {
        QPixmap noSaveData(":/graphic/noSaveData.png");
        ui->preview->setStyleSheet("background: transparent ;");
        ui->preview->setPixmap(noSaveData);
        return;
    }
    QString filename = QFileDialog::getSaveFileName(this, ("Save Skin"), "C:/Users/", ("PNG Image (*.png)"));
    QFile file(filename);
    file.open(QIODevice::WriteOnly);
    file.write(pngData);
    file.close();
}

void MainWindow::on_save_clicked()
{
    if (pngData.isEmpty())
    {
        QPixmap noSaveData(":/graphic/noSaveData.png");
        ui->preview->setStyleSheet("background: transparent ;");
        ui->preview->setPixmap(noSaveData);
        return;
    }
    QString filename = QFileDialog::getSaveFileName(this, ("Save Skin"), "C:/Users/", ("PNG Image (*.png)"));
    QFile file(filename);
    file.open(QIODevice::WriteOnly);
    file.write(pngData);
    file.close();
}

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