Set default background color for widgets on iOS

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

@@ -89,21 +89,17 @@ def set_color(self, color):
         # By default, color can't be changed
         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)
+    def set_background_color(self, color, is_native_color=False):
+        if is_native_color:
+            self.native.backgroundColor = color
         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
+            default_background_color = getattr(self, "_default_background_color", None)
+            if default_background_color is None:
+                default_background_color = UIColor.systemBackgroundColor()
+
+            self.native.backgroundColor = (
+                default_background_color if color is None else native_color(color)
+            )
 
     # INTERFACE
     def add_child(self, child):

iOS/src/toga_iOS/widgets/box.py

@@ -1,7 +1,7 @@
 from rubicon.objc import objc_property
 from travertino.size import at_least
 
-from toga_iOS.libs import UIView
+from toga_iOS.libs import UIColor, UIView
 from toga_iOS.widgets.base import Widget
 
 
@@ -19,12 +19,10 @@ def create(self):
         self.native.interface = self.interface
         self.native.impl = self
 
+        self._default_background_color = UIColor.clearColor
         # 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

@@ -38,6 +38,7 @@ def create(self):
 
         self._icon = None
 
+        self._default_background_color = None
         # Add the layout constraints
         self.add_constraints()
 
@@ -68,10 +69,10 @@ 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 native_color(color)),
+            is_native_color=True,
+        )
 
     def set_font(self, font):
         self.native.titleLabel.font = font._impl.native

iOS/src/toga_iOS/widgets/canvas.py

@@ -15,7 +15,7 @@
 )
 from travertino.size import at_least
 
-from toga.colors import BLACK, TRANSPARENT, color
+from toga.colors import BLACK, TRANSPARENT, color as toga_color
 from toga.constants import Baseline, FillRule
 from toga_iOS.colors import native_color
 from toga_iOS.images import nsdata_to_bytes
@@ -70,6 +70,8 @@ def create(self):
         self.native.interface = self.interface
         self.native.impl = self
 
+        self._default_background_color = UIColor.clearColor
+
         # Add the layout constraints
         self.add_constraints()
 
@@ -260,7 +262,7 @@ def _line_height(self, font):
     def measure_text(self, text, font):
         # We need at least a fill color to render, but that won't change the size.
         sizes = [
-            self._render_string(line, font, fill_color=color(BLACK)).size()
+            self._render_string(line, font, fill_color=toga_color(BLACK)).size()
             for line in text.splitlines()
         ]
         return (

iOS/src/toga_iOS/widgets/imageview.py

@@ -1,7 +1,5 @@
-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.libs import UIColor, UIImageView, UIViewContentMode
 from toga_iOS.widgets.base import Widget
 
 
@@ -15,13 +13,9 @@ def create(self):
         self.native.setTranslatesAutoresizingMaskIntoConstraints_(False)
         self.native.setAutoresizesSubviews_(False)
 
-        self.add_constraints()
+        self._default_background_color = UIColor.clearColor
 
-    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)
+        self.add_constraints()
 
     def set_image(self, image):
         if image:

iOS/src/toga_iOS/widgets/label.py

@@ -3,11 +3,11 @@
 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,
     NSTextAlignment,
+    UIColor,
     UILabel,
 )
 from toga_iOS.widgets.base import Widget
@@ -38,6 +38,8 @@ def create(self):
         # We shouldn't ever word wrap; if faced with that option, clip.
         self.native.lineBreakMode = NSLineBreakByClipping
 
+        self._default_background_color = UIColor.clearColor
+
         # Add the layout constraints
         self.add_constraints()
 
@@ -47,12 +49,6 @@ def set_alignment(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_alignment(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/progressbar.py

@@ -2,7 +2,7 @@
 
 from travertino.size import at_least
 
-from toga_iOS.libs import CGSize, UIProgressView, UIProgressViewStyle
+from toga_iOS.libs import CGSize, UIColor, UIProgressView, UIProgressViewStyle
 from toga_iOS.widgets.base import Widget
 
 # Implementation notes
@@ -41,6 +41,8 @@ def create(self):
         self.native = UIProgressView.alloc().initWithProgressViewStyle_(
             UIProgressViewStyle.Default
         )
+        self._default_background_color = UIColor.clearColor
+
         self.add_constraints()
 
         self._running = False

iOS/src/toga_iOS/widgets/scrollcontainer.py

@@ -2,7 +2,7 @@
 from travertino.size import at_least
 
 from toga_iOS.container import Container
-from toga_iOS.libs import UIScrollView
+from toga_iOS.libs import UIColor, UIScrollView
 from toga_iOS.widgets.base import Widget
 
 
@@ -31,6 +31,8 @@ def create(self):
         self.native.impl = self
         self.native.delegate = self.native
 
+        self._default_background_color = UIColor.clearColor
+
         # UIScrollView doesn't have a native ability to disable a scrolling direction;
         # it's handled by controlling the scrollable area.
         self._allow_horizontal = True
@@ -68,9 +70,6 @@ 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

@@ -83,9 +83,6 @@ def set_alignment(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/slider.py

@@ -2,6 +2,7 @@
 from travertino.size import at_least
 
 from toga_iOS.libs import (
+    UIColor,
     UIControlEventTouchCancel,
     UIControlEventTouchDown,
     UIControlEventTouchUpInside,
@@ -49,6 +50,8 @@ def create(self):
         self.native.interface = self.interface
         self.native.impl = self
 
+        self._default_background_color = UIColor.clearColor
+
         # Dummy values used during initialization.
         self.value = 0
         self.min_value = 0

iOS/src/toga_iOS/widgets/textinput.py

@@ -138,9 +138,6 @@ def set_alignment(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)