How to implement a simple QFileDialog in a QGIS plugin

Question

I'm building a QGIS plugin which only requires user interaction to select a save location for an output file. I used Plugin Builder to create a template and assumed I could simply replace the template dialog with a QFileDialog object. Here's the relevant code:

def run(self):
    """Run method that performs all the real work"""

    # Create the dialog with elements (after translation) and keep reference
    # Only create GUI ONCE in callback, so that it will only load when the plugin is started
    if self.first_start == True:
        self.first_start = False
        self.dlg = QFileDialog(self.iface)
        self.dlg.setFileMode(QFileDialog.AnyFile)
        self.dlg.setNameFilter(self.tr("Zip files (*.zip)"))
        # self.dlg = GiftWrapDialog()

    # show the dialog
    self.dlg.show()
    # Run the dialog event loop
    result = self.dlg.exec_()
    # See if OK was pressed
    if result:
        # Do something useful here - delete the line containing pass and
        # substitute with your code.
        pass

This code throws an error when I try to run the plugin:

TypeError: arguments did not match any overloaded call:   QFileDialog(QWidget, Union[Qt.WindowFlags, Qt.WindowType]): argument 1 has unexpected type 'QgisInterface'   QFileDialog(parent: QWidget = None, caption: str = '', directory: str = '', filter: str = ''): argument 1 has unexpected type 'QgisInterface' 

Is there any way for my plugin to simply show a standard file dialog without having to create my own dialog?

Answer 1

There may be different types of QFileDialog in a QGIS plugin and it is preferable do not put it in run method. In the case of 'getSaveFileName' QFileDialog type, you have a following code snippet of one of my plugins (built with Plugin Builder). The 'select_output_file' function was placed before run method and it is connected to a QPushButton associated to QFileDialog (for placing file name there is also associated a QLineEdit object).

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from PyQt5.QtWidgets import QAction, QFileDialog
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    def add_action(
        self,
        icon_path,
        text,
        callback,
        enabled_flag=True,
        add_to_menu=True,
        add_to_toolbar=True,
        status_tip=None,
        whats_this=None,
        parent=None):
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        self.dlg.lineEdit.clear()
        self.dlg.pushButton.clicked.connect(self.select_output_file)

        okBtn = self.dlg.okButton
        okBtn.clicked.connect(self.input_values)

        return action
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    def select_output_file(self):

        filename = QFileDialog.getSaveFileName(self.dlg, "Select output file ","", '*.tif')
        ext = ".tif"
        ext_filename = filename[0][-4:]

        if ext_filename != ext:
            filename[0] += ext 

        self.dlg.lineEdit.setText(filename[0])
.
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.

In following code snippet you have an example of 'getExistingDirectory' QFileDialog where I also used Plugin Builder to create a template.

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from PyQt5.QtGui import QAction, QIcon, QTableWidgetItem, QFileDialog
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    def add_action(
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        self.dlg.lineEdit.clear()
        self.dlg.pushButton.clicked.connect(self.select_output_directory)
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    def select_output_directory(self):

        folder = str(QFileDialog.getExistingDirectory(self.dlg, "Select Directory"))

        self.dlg.lineEdit.setText(folder)
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