New Demo Program - Make windows and PySimpleGUI calls from a thread.

DemoPrograms/Demo_Multithreaded_Delegate_Appear_To_Make_PSG_Calls_From_Thread.py

@@ -0,0 +1,145 @@
+import PySimpleGUI as sg
+import time
+import threading
+
+"""
+    Demo - Multi-threaded - Show Windows and perform other PySimpleGUI calls in what appread to be from a thread
+    
+    Just so that it's clear, you CANNOT make PySimpleGUI calls directly from a thread.  There is ONE exception to this
+    rule.  A thread may call  window.write_event_values which enables it to communicate to a window through the window.read calls.
+
+    The main GUI will not be visible on your screen nor on your taskbar despite running in the background.  The calls you 
+    make, such as popup, or even Window.read will create windows that your user will see.
+    
+    The basic function that you'll use in your thread has this format:
+        make_delegate_call(lambda: sg.popup('This is a popup', i, auto_close=True, auto_close_duration=2, keep_on_top=True, non_blocking=True))
+
+    Everything after the "lambda" looks exactly like a PySimpleGUI call.
+    If you want to display an entire window, then the suggestion is to put it into a function and pass the function to make_delegate_call
+    
+    Note - the behavior of variables may be a bit of a surprise as they are not evaluated until the mainthread processes the event.  This means
+    in the example below that the counter variable being passed to the popup will not appear to be counting correctly.  This is because the
+    value shown will be the value at the time the popup is DISPLAYED, not the value when the make_delegate_call was made. 
+    
+    Copyright 2022 PySimpleGUI
+"""
+
+
+# Design decision was to make the window a global.  You can just as easily pass it to your function after initizing your window
+# But there becomes a problem then of wheere do you place the thread startup code.  Using this global decouples them so that
+# the thread is not started in the function that makes and executes the GUI
+
+window:sg.Window = None
+
+# M""MMMM""M
+# M. `MM' .M
+# MM.    .MM .d8888b. dP    dP 88d888b.
+# MMMb  dMMM 88'  `88 88    88 88'  `88
+# MMMM  MMMM 88.  .88 88.  .88 88
+# MMMM  MMMM `88888P' `88888P' dP
+# MMMMMMMMMM
+#
+# M""""""""M dP                                        dP
+# Mmmm  mmmM 88                                        88
+# MMMM  MMMM 88d888b. 88d888b. .d8888b. .d8888b. .d888b88
+# MMMM  MMMM 88'  `88 88'  `88 88ooood8 88'  `88 88'  `88
+# MMMM  MMMM 88    88 88       88.  ... 88.  .88 88.  .88
+# MMMM  MMMM dP    dP dP       `88888P' `88888P8 `88888P8
+# MMMMMMMMMM
+
+def the_thread():
+    """
+    This is code that is unique to your application.  It wants to "make calls to PySimpleGUI", but it cannot directly do so.
+    Instead it will send the request to make the call to the mainthread that is running the GUI.
+
+    :return:
+    """
+
+    # loop 10 times, each time making 2 different popup calls that indicate they should autoclose and not block the main GUI
+    for i in range(10):
+        time.sleep(.2)
+        make_delegate_call(lambda: sg.popup('This is a popup', i, auto_close=True, auto_close_duration=2, keep_on_top=True, non_blocking=True))
+        make_delegate_call(lambda: sg.popup_scrolled(__file__, sg.get_versions(), auto_close=True, auto_close_duration=1.5, non_blocking=True))
+
+    # when finished and ready to stop, tell the main GUI to exit
+    window.write_event_value('-THREAD EXIT-', None)
+
+
+# -------------------------------------------------------------------------------------------------------- #
+
+# The remainder of the code is part of the overall design pattern.  You should copy this code
+# and use it as the basis for creating this time of delegated PySimpleGUI calls
+
+
+# M""""""'YMM                   oo
+# M  mmmm. `M
+# M  MMMMM  M .d8888b. .d8888b. dP .d8888b. 88d888b.
+# M  MMMMM  M 88ooood8 Y8ooooo. 88 88'  `88 88'  `88
+# M  MMMM' .M 88.  ...       88 88 88.  .88 88    88
+# M       .MM `88888P' `88888P' dP `8888P88 dP    dP
+# MMMMMMMMMMM                           .88
+#                                   d8888P
+# MM"""""""`YM            dP     dP
+# MM  mmmmm  M            88     88
+# M'        .M .d8888b. d8888P d8888P .d8888b. 88d888b. 88d888b.
+# MM  MMMMMMMM 88'  `88   88     88   88ooood8 88'  `88 88'  `88
+# MM  MMMMMMMM 88.  .88   88     88   88.  ... 88       88    88
+# MM  MMMMMMMM `88888P8   dP     dP   `88888P' dP       dP    dP
+# MMMMMMMMMMMM
+
+def make_delegate_call(func):
+    """
+    Make a deletegate call to PySimpleGUI.
+
+    :param func:    A lambda expression most likely.  It's a function that will be called by the mainthread that's executing the GUI
+    :return:
+    """
+    if window is not None:
+        window.write_event_value('-THREAD DELEGATE-', func)
+
+
+#                     oo
+#
+# 88d8b.d8b. .d8888b. dP 88d888b.
+# 88'`88'`88 88'  `88 88 88'  `88
+# 88  88  88 88.  .88 88 88    88
+# dP  dP  dP `88888P8 dP dP    dP
+
+def main():
+    global window
+
+    # create a window.  A key is needed so that the values dictionary will return the thread's value as a key
+    layout = [[sg.Text('Window will not be visible', k='-T-')]]
+
+    # set the window to be both invisible and have no taskbar icon
+    window = sg.Window('Invisible window', layout, no_titlebar=True, alpha_channel=0)
+
+    while True:
+        event, values = window.read()
+        if event in ('Exit', sg.WIN_CLOSED):
+            break
+        # if the event is from the thread, then the value is the function that should be called
+        if event == '-THREAD DELEGATE-':
+            try:
+                values[event]()
+            except Exception as e:
+                sg.popup_error_with_traceback('Error calling your function passed to GUI', event, values, e)
+        elif event == '-THREAD EXIT-':
+            break
+    window.close()
+
+
+# MP""""""`MM   dP                       dP
+# M  mmmmm..M   88                       88
+# M.      `YM d8888P .d8888b. 88d888b. d8888P dP    dP 88d888b.
+# MMMMMMM.  M   88   88'  `88 88'  `88   88   88    88 88'  `88
+# M. .MMM'  M   88   88.  .88 88         88   88.  .88 88.  .88
+# Mb.     .dM   dP   `88888P8 dP         dP   `88888P' 88Y888P'
+# MMMMMMMMMMM                                          88
+#                                                      dP
+
+if __name__ == '__main__':
+    # first your thread will be started
+    threading.Thread(target=the_thread, daemon=True).start()
+    # then startup the main GUI
+    main()