README.md

HowTo: singleinstancedlg

This sample shows how to create a single instance modeless dialog.

Goal:

• learn how how to use findChild in PySide to create a single instance dialog

Explanations

The sample creates a custom PySide dialog and calls setObjectName on it with a unique name. The show_dialog() function only creates a new dialog if findChild cannot find the QDialog with the name specified in setObjectName. The dialog (either found or created) is then shown by calling dialog.show().

Understanding the code

In ui.py, we first create a new custom dialog class.

from qtpy.QtWidgets import QWidget, QDialog, QVBoxLayout, QPushButton
from pymxs import runtime as rt

MAIN_WINDOW = QWidget.find(rt.windows.getMAXHWND())

class PyMaxDialog(QDialog):
    """
    Custom dialog attached to the 3ds Max main window
    """

We define a class variable that will be the unique name of this dialog. We use the filename as a unique name:

    unique_name = __file__

In the constructor we assign a unique name to the dialog:

    def __init__(self, parent):
        super(PyMaxDialog, self).__init__(parent)
        self.setWindowTitle('Single Instance Dialog')

        # keep track of being unique
        self.setObjectName(PyMaxDialog.unique_name)

We then define a show_dialog function that only creates a dialog if an existing one cannot be found:

def show_dialog():
    '''Show the dialog without duplicating it'''
    dialog = MAIN_WINDOW.findChild(QDialog, PyMaxDialog.unique_name)
    if dialog is None:
        dialog = PyMaxDialog(MAIN_WINDOW)
    dialog.show()