New demo to show how to make Multline element input justification correct

DemoPrograms/Demo_Multiline_Elem_Input_Justification.py

@@ -0,0 +1,46 @@
+"""
+    Multline Element - Input Justification
+
+    The justification of text for the Multiline element defaults to Left Justified
+    Because of the way tkinter's widget works, setting the justification when creating the element
+    is not enough to provide the correct justification.
+
+    The demo shows you the technique to achieve justified input
+
+    Key points:
+        * Enable events on the multiline
+        * Add 2 lines of code to your event loop
+            * If get mline element event
+                * Set the contents of the multline to be the correct justificaiton
+
+    Copyright 2021 PySimpleGUI
+"""
+
+import PySimpleGUI as sg
+
+def main():
+    justification = 'l'     # start left justified
+
+    layout = [[sg.Text('Multiline Element Input Justification')],
+              [sg.Multiline(size=(40,10), key='-MLINE-', justification=justification, enable_events=True, autoscroll=True)],
+               # We'll be fancy and allow user to choose which justification to use in the demo
+              [sg.Radio('Left', 0, True, k='-L-'), sg.Radio('Center', 0, k='-C-'),sg.Radio('Right', 0, k='-R-'),],
+              [sg.Button('Go'), sg.Button('Exit')]]
+
+    window = sg.Window('Window Title', layout, keep_on_top=True, resizable=True, finalize=True)
+
+    while True:             # Event Loop
+        event, values = window.read()
+        if event == sg.WIN_CLOSED or event == 'Exit':
+            break
+        # Get desired justication from radio buttons. You don't need this if you know your justification already
+        justification = 'l' if values['-L-'] else 'r' if values['-R-'] else 'c'
+
+        # This is the important bit of code. It sets the current contents of the multiline to be the correct justification
+        if event == '-MLINE-':
+            window['-MLINE-'].update(values['-MLINE-'][:-1], justification=justification)
+
+    window.close()
+
+if __name__ == '__main__':
+    main()