Provide for splash screens.

README.md

@@ -1036,7 +1036,11 @@ See `demos/plot.py` for an example of multi-screen design, or
 
 ## 4.2 Constructor
 
-This takes no arguments.
+This takes one optional argument.
+ * `writer=None` In general a `Screen` must have at least on active widget. In
+ the special case where there are none (e.g. a splash screen), a `Writer`
+ instance should be passed. Application code should close the splash screen by
+ issuing `Screen.back()`.
 
 ## 4.3 Callback methods
 

gui/core/ugui.py

@@ -477,7 +477,7 @@ class Screen:
     def shutdown(cls):
         cls.is_shutdown.set()  # Tell monitor() to shutdown
 
-    def __init__(self):
+    def __init__(self, writer=None):
         self.lstactive = []  # Controls which respond to Select button
         self.selected_obj = None  # Index of currently selected object
         self.displaylist = []  # All displayable objects
@@ -491,6 +491,8 @@ class Screen:
             asyncio.create_task(self._garbage_collect())
         Screen.current_screen = self
         self.parent = None
+        if writer is not None:  # Special case of no active widgets (e.g. popup message)
+            DummyWidget(writer, self)  # Invisible active widget
 
     def _do_open(self, old_screen):  # Window overrides
         dev = display.usegrey(False)
@@ -621,7 +623,7 @@ class Window(Screen):
         fgcolor=None,
         writer=None,
     ):
-        Screen.__init__(self)
+        Screen.__init__(self, writer)
         self.row = row
         self.col = col
         self.height = height
@@ -629,8 +631,6 @@ class Window(Screen):
         self.draw_border = draw_border
         self.fgcolor = fgcolor if fgcolor is not None else color_map[FG]
         self.bgcolor = bgcolor if bgcolor is not None else color_map[BG]
-        if writer is not None:  # Special case of popup message
-            DummyWidget(writer, self)  # Invisible active widget
 
     def _do_open(self, old_screen):
         dev = display.usegrey(False)
@@ -898,8 +898,8 @@ class DummyWidget(Widget):
             window.col + 1,
             4,
             4,
-            window.fgcolor,
-            window.bgcolor,
+            None,
+            None,
             False,
             None,
             True,

gui/demos/screen_change.py

@@ -1,7 +1,7 @@
 # screen_change.py Minimal micro-gui demo showing a Button causing a screen change.
 
 # Released under the MIT License (MIT). See LICENSE.
-# Copyright (c) 2021 Peter Hinch
+# Copyright (c) 2021-2025 Peter Hinch
 
 # hardware_setup must be imported before other modules because of RAM use.
 import hardware_setup  # Create a display instance
@@ -13,41 +13,62 @@ from gui.core.writer import CWriter
 # Font for CWriter
 import gui.fonts.arial10 as font
 from gui.core.colors import *
+import asyncio
+import time
 
 # Defining a button in this way enables it to be re-used on
 # multiple Screen instances. Note that a Screen class is
 # passed, not an instance.
-def fwdbutton(wri, row, col, cls_screen, text='Next'):
+def fwdbutton(wri, row, col, cls_screen, text="Next"):
     def fwd(button):
         Screen.change(cls_screen)  # Callback
 
-    Button(wri, row, col, callback = fwd,
-           fgcolor = BLACK, bgcolor = GREEN,
-           text = text, shape = RECTANGLE)
+    Button(wri, row, col, callback=fwd, fgcolor=BLACK, bgcolor=GREEN, text=text, shape=RECTANGLE)
+
 
 wri = CWriter(ssd, font, GREEN, BLACK, verbose=False)
 
 # This screen overlays BaseScreen.
 class BackScreen(Screen):
-
     def __init__(self):
         super().__init__()
-        Label(wri, 2, 2, 'New screen.')
+        Label(wri, 2, 2, "New screen.")
         CloseButton(wri)
 
 
+# The splash screen is a special case of a Screen with no active widgets.
+class SplashScreen(Screen):
+    def __init__(self):
+        super().__init__(wri)  # No sctive widgets: must pass writer
+        Label(wri, 10, 10, "Splash screen")
+        Label(wri, 40, 10, "Please wait", fgcolor=YELLOW)
+
+    def after_open(self):  # Cle after a period
+        asyncio.create_task(self.close_me())
+
+    async def close_me(self):
+        await asyncio.sleep(3)
+        Screen.back()
+
+
 class BaseScreen(Screen):
-
     def __init__(self):
 
         super().__init__()
-        Label(wri, 2, 2, 'Base screen.')
+        Label(wri, 2, 2, "Base screen.")
         fwdbutton(wri, 40, 2, BackScreen)
         CloseButton(wri)
+        self.splash_done = False
+
+    def after_open(self):
+        if not self.splash_done:  # Only show splash on initial opening.
+            Screen.change(SplashScreen)
+        self.splash_done = True
 
 
 def test():
-    print('Screen change demo.')
+    print("Screen change demo.")
     Screen.change(BaseScreen)  # Pass class, not instance!
 
+
 test()