Set default background color for widgets on iOS (#3009)

Simplifies the implementation of background color on iOS so that the default background color for most widgets is transparent, allowing the default window background to be visible.

changes/767.bugfix.rst

@@ -0,0 +1 @@
+On iOS, the default background color is now TRANSPARENT for Box, Canvas, ImageView, Label, ProgressBar, ScrollContainer and Slider widgets.

iOS/src/toga_iOS/widgets/base.py

@@ -2,7 +2,6 @@
 
 from toga_iOS.colors import native_color
 from toga_iOS.constraints import Constraints
-from toga_iOS.libs import UIColor
 
 
 class Widget:
@@ -88,20 +87,7 @@ def set_color(self, color):
         pass
 
     def set_background_color(self, color):
-        # By default, background color can't be changed
-        pass
-
-    # TODO: check if it's safe to make this the default implementation.
-    def set_background_color_simple(self, value):
-        if value:
-            self.native.backgroundColor = native_color(value)
-        else:
-            try:
-                # systemBackgroundColor() was introduced in iOS 13
-                # We don't test on iOS 12, so mark the other branch as nocover
-                self.native.backgroundColor = UIColor.systemBackgroundColor()
-            except AttributeError:  # pragma: no cover
-                self.native.backgroundColor = UIColor.whiteColor
+        self.native.backgroundColor = None if color is None else native_color(color)
 
     # INTERFACE
     def add_child(self, child):

iOS/src/toga_iOS/widgets/box.py

@@ -19,9 +19,6 @@ def create(self):
         # Add the layout constraints
         self.add_constraints()
 
-    def set_background_color(self, value):
-        self.set_background_color_simple(value)
-
     def rehint(self):
         self.interface.intrinsic.width = at_least(0)
         self.interface.intrinsic.height = at_least(0)

iOS/src/toga_iOS/widgets/button.py

@@ -68,10 +68,7 @@ def set_color(self, color):
             )
 
     def set_background_color(self, color):
-        if color == TRANSPARENT or color is None:
-            self.native.backgroundColor = None
-        else:
-            self.native.backgroundColor = native_color(color)
+        super().set_background_color(None if color in {None, TRANSPARENT} else color)
 
     def set_font(self, font):
         self.native.titleLabel.font = font._impl.native

iOS/src/toga_iOS/widgets/imageview.py

@@ -1,6 +1,4 @@
-from toga.colors import TRANSPARENT
 from toga.widgets.imageview import rehint_imageview
-from toga_iOS.colors import native_color
 from toga_iOS.libs import UIImageView, UIViewContentMode
 from toga_iOS.widgets.base import Widget
 
@@ -17,12 +15,6 @@ def create(self):
 
         self.add_constraints()
 
-    def set_background_color(self, color):
-        if color == TRANSPARENT or color is None:
-            self.native.backgroundColor = native_color(TRANSPARENT)
-        else:
-            self.native.backgroundColor = native_color(color)
-
     def set_image(self, image):
         if image:
             self.native.image = image._impl.native

iOS/src/toga_iOS/widgets/label.py

@@ -3,7 +3,6 @@
 from rubicon.objc import CGRect, NSInteger, NSMakeRect, objc_method, send_super
 from travertino.size import at_least
 
-from toga.colors import TRANSPARENT
 from toga_iOS.colors import native_color
 from toga_iOS.libs import (
     NSLineBreakByClipping,
@@ -47,12 +46,6 @@ def set_text_align(self, value):
     def set_color(self, value):
         self.native.textColor = native_color(value)
 
-    def set_background_color(self, color):
-        if color == TRANSPARENT or color is None:
-            self.native.backgroundColor = native_color(TRANSPARENT)
-        else:
-            self.native.backgroundColor = native_color(color)
-
     def set_font(self, font):
         self.native.font = font._impl.native
 

iOS/src/toga_iOS/widgets/multilinetextinput.py

@@ -141,9 +141,6 @@ def set_color(self, value):
         self.native.textColor = color
         self.placeholder_label.textColor = color
 
-    def set_background_color(self, color):
-        self.set_background_color_simple(color)
-
     def set_text_align(self, value):
         self.native.textAlignment = NSTextAlignment(value)
 

iOS/src/toga_iOS/widgets/numberinput.py

@@ -117,9 +117,6 @@ def set_font(self, font):
     def set_color(self, color):
         self.native.textColor = native_color(color)
 
-    def set_background_color(self, color):
-        self.set_background_color_simple(color)
-
     def rehint(self):
         # Height of a text input is known.
         fitting_size = self.native.systemLayoutSizeFittingSize(CGSize(0, 0))

iOS/src/toga_iOS/widgets/scrollcontainer.py

@@ -68,9 +68,6 @@ def content_refreshed(self, container):
 
         self.native.contentSize = NSMakeSize(width, height)
 
-    def set_background_color(self, value):
-        self.set_background_color_simple(value)
-
     def rehint(self):
         self.interface.intrinsic.width = at_least(self.interface._MIN_WIDTH)
         self.interface.intrinsic.height = at_least(self.interface._MIN_HEIGHT)

iOS/src/toga_iOS/widgets/selection.py

@@ -89,9 +89,6 @@ def set_text_align(self, value):
     def set_color(self, color):
         self.native.textColor = native_color(color)
 
-    def set_background_color(self, color):
-        self.set_background_color_simple(color)
-
     def set_font(self, font):
         self.native.font = font._impl.native
 

iOS/src/toga_iOS/widgets/textinput.py

@@ -138,9 +138,6 @@ def set_text_align(self, value):
     def set_color(self, color):
         self.native.textColor = native_color(color)
 
-    def set_background_color(self, color):
-        self.set_background_color_simple(color)
-
     def set_font(self, font):
         self.native.font = font._impl.native
 

testbed/tests/widgets/test_button.py

@@ -101,6 +101,9 @@ async def test_press(widget, probe):
 
 async def test_background_color_transparent(widget, probe):
     "Buttons treat background transparency as a color reset."
+    del widget.style.background_color
+    original_background_color = probe.background_color
+
     widget.style.background_color = TRANSPARENT
-    await probe.redraw("Button background color should be transparent")
-    assert_color(probe.background_color, None)
+    await probe.redraw("Button background color should be reset to the default color")
+    assert_color(probe.background_color, original_background_color)