Disable file name box in QFileDialog

I used a QFileDialog to open a browser. Here is my code:

QString filePath = QFileDialog::getSaveFileName(this,
                                               "Export Xml", "PluginPythonQt",
                                                "Xml files (*.xml)");

When excute it will show a dialog like this:

I want to disable the "File name:" box in the picture or prevent user to enter a new name. How can i do that ? Thanks.