theme_previewer changes. (#21)

* theme_previewer changes.
User can now choose a theme by clicking on the OK button of
the previewed theme. The function returns the theme name.

e.g.

    new_theme = sg.preview_all_look_and_feel_themes(scrollable=True,columns=8)
    if new_theme:
        sg.theme(new_theme)

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: RoboPickle

FreeSimpleGUI/__init__.py

@@ -9109,6 +9109,7 @@ def theme_previewer(columns=12, scrollable=False, scroll_area_size=(None, None),
     """
     Displays a "Quick Reference Window" showing all of the different Look and Feel settings that are available.
     They are sorted alphabetically.  The legacy color names are mixed in, but otherwise they are sorted into Dark and Light halves
+    If one of the "OK" buttons are pressed then that theme name is returned.
 
     :param columns:          The number of themes to display per row
     :type columns:           int
@@ -9138,10 +9139,10 @@ def theme_previewer(columns=12, scrollable=False, scroll_area_size=(None, None),
 
     win_bg = 'black'
 
-    def sample_layout():
+    def sample_layout(theme_name):
         return [
             [Text('Text element'), InputText('Input data here', size=(10, 1))],
-            [Button('Ok'), Button('Disabled', disabled=True), Slider((1, 10), orientation='h', size=(5, 15))],
+            [Button('Ok', key=f"choose_{theme_name}", tooltip=f"Choose {theme_name}"), Button('Disabled', disabled=True), Slider((1, 10), orientation='h', size=(5, 15))],
         ]
 
     names = list_of_look_and_feel_values()
@@ -9161,7 +9162,7 @@ def sample_layout():
         if not count % columns:
             col_layout += [row]
             row = []
-        row += [Frame(theme_name, sample_layout() if not web else [[T(theme_name)]] + sample_layout(), pad=(2, 2))]
+        row += [Frame(theme_name, sample_layout(theme_name) if not web else [[T(theme_name)]] + sample_layout(theme_name), pad=(2, 2))]
     if row:
         col_layout += [row]
 
@@ -9188,8 +9189,10 @@ def sample_layout():
         modal=True,
     )
     window['-COL-'].expand(True, True, True)  # needed so that col will expand with the window
-    window.read(close=True)
+    event, values = window.read(close=True)
     theme(current_theme)
+    if event and event.startswith('choose_'):
+        return event[7:]
 
 
 preview_all_look_and_feel_themes = theme_previewer