drag and drop multi document interface sample code

dnd_mdi.py

import os, sys
from PySide2.QtWidgets import QTextEdit, QApplication, QMainWindow, QMdiArea, QMdiSubWindow, QMessageBox

class MainWindow(QMainWindow):
    def __init__(self, parent=None):
        super().__init__(parent)
        self.setCentralWidget(MdiArea())

class MdiArea(QMdiArea):
    def __init__(self, parent=None):
        super(MdiArea, self).__init__(parent)
        self.setAcceptDrops(True)
    
    def dragEnterEvent(self, event):
        event.acceptProposedAction()

    def dropEvent(self, event):
        txts = []
        for url in event.mimeData().urls():
            if (url.scheme()=='file') & (url.path().endswith('.txt')):
                sub = QMdiSubWindow()
                sub.setWidget(QTextEdit())
                sub.setWindowTitle(os.path.basename(url.path()))
                self.addSubWindow(sub)
                sub.show()

            else:
                dialog = QMessageBox()
                dialog.setWindowTitle("Error: Invalid File")
                dialog.setText("Only .txt files are accepted")
                dialog.setIcon(QMessageBox.Warning)
                dialog.exec_()
                return

if __name__ == "__main__":
    app = QApplication(sys.argv)
    win = MainWindow()
    win.show()
    sys.exit(app.exec_())