From 8f6db74f8316220f31bb54f4fa1089f305f52be8 Mon Sep 17 00:00:00 2001
From: PySimpleGUI <PySimpleGUI@PySimpleGUI.com>
Date: Mon, 23 Sep 2019 12:10:10 -0400
Subject: [PATCH] New demo program that simulates callbacks using a dictionary

---
 .../Demo_Event_Callback_Simulation.py         | 53 +++++++++++++++++++
 1 file changed, 53 insertions(+)
 create mode 100644 DemoPrograms/Demo_Event_Callback_Simulation.py

diff --git a/DemoPrograms/Demo_Event_Callback_Simulation.py b/DemoPrograms/Demo_Event_Callback_Simulation.py
new file mode 100644
index 00000000..d3642368
--- /dev/null
+++ b/DemoPrograms/Demo_Event_Callback_Simulation.py
@@ -0,0 +1,53 @@
+import PySimpleGUI as sg
+# import PySimpleGUIQt as sg
+# import PySimpleGUIWx as sg
+
+'''
+    Event Callback Simulation
+    
+    This design pattern simulates callbacks for events.  
+    This is NOT the "normal" way things work in PySimpleGUI and is an architecture that is actively discouraged
+    Unlike tkinter, Qt, etc, PySimpleGUI does not utilize callback
+    functions as a mechanism for communicating when button presses or other events happen.
+    BUT, should you want to quickly convert some existing code that does use callback functions, then this
+    is one way to do a "quick and dirty" port to PySimpleGUI.
+'''
+
+# The callback functions
+# These callbacks all display a message in a non-blocking way and immediately return
+def button1(event, values):
+    sg.popup_quick_message('Button 1 callback', background_color='red', text_color='white')
+
+def button2(event, values):
+    sg.popup_quick_message('Button 2 callback', background_color='green', text_color='white')
+
+def catch_all(event, values):
+    sg.popup_quick_message(f'An unplanned event = "{event}" happend', background_color='blue', text_color='white', auto_close_duration=6)
+
+# Lookup dictionary that maps event to function to call. In this case, only 2 event have defined callbacks
+func_dict = {'1':button1, '2':button2}
+
+# Layout the design of the GUI
+layout = [[sg.Text('Please click a button')],
+          [sg.Button('1'), sg.Button('2'), sg.Button('Not defined', key='-MY-KEY-'), sg.Quit()]]
+
+# Show the Window to the user
+window = sg.Window('Button callback example', layout)
+
+# Event loop. Read buttons, make callbacks
+while True:
+    # Read the Window
+    event, values = window.read()
+    # Lookup event in function dictionary and call the function, passing in the event and values variables
+    try:
+        func_dict[event](event, values)   # Call function with event and values
+    except:
+        catch_all(event, values)
+    # See if should close the window
+    if event in ('Quit', None):         # normally this is done IMMEDIATELY after the read
+        break
+
+window.close()
+
+# All done!
+sg.popup_auto_close('Done... this window auto closes')
\ No newline at end of file