Enforce min layout size as window size

android/src/toga_android/container.py

@@ -1,32 +1,40 @@
 from .libs.android.widget import RelativeLayout, RelativeLayout__LayoutParams
+from .widgets.base import Scalable
 
 
-class Container:
+class Container(Scalable):
     def init_container(self, native_parent):
-        self.width = self.height = 0
-
         context = native_parent.getContext()
+        self.native_parent = native_parent
+        self.init_scale(context)
+        self.native_width = self.native_height = 0
+        self.content = None
+
         self.native_content = RelativeLayout(context)
         native_parent.addView(self.native_content)
 
-        self.dpi = context.getResources().getDisplayMetrics().densityDpi
-        # Toga needs to know how the current DPI compares to the platform default,
-        # which is 160: https://developer.android.com/training/multiscreen/screendensities
-        self.baseline_dpi = 160
-        self.scale = self.dpi / self.baseline_dpi
+    @property
+    def width(self):
+        return self.scale_out(self.native_width)
+
+    @property
+    def height(self):
+        return self.scale_out(self.native_height)
 
     def set_content(self, widget):
         self.clear_content()
         if widget:
             widget.container = self
+            self.content = widget
 
     def clear_content(self):
-        if self.interface.content:
-            self.interface.content._impl.container = None
+        if self.content:
+            self.content.container = None
+            self.content = None
 
     def resize_content(self, width, height):
-        if (self.width, self.height) != (width, height):
-            self.width, self.height = (width, height)
+        if (self.native_width, self.native_height) != (width, height):
+            self.native_width, self.native_height = (width, height)
             if self.interface.content:
                 self.interface.content.refresh()
 
@@ -37,8 +45,8 @@ def refreshed(self):
         # meaning of the (int, int) constructor.
         lp = self.native_content.getLayoutParams()
         layout = self.interface.content.layout
-        lp.width = max(self.width, layout.width)
-        lp.height = max(self.height, layout.height)
+        lp.width = max(self.native_width, self.scale_in(layout.width))
+        lp.height = max(self.native_height, self.scale_in(layout.height))
         self.native_content.setLayoutParams(lp)
 
     def add_content(self, widget):

android/src/toga_android/widgets/base.py

@@ -1,4 +1,7 @@
-from abc import abstractmethod
+from abc import ABC, abstractmethod
+from decimal import ROUND_HALF_EVEN, ROUND_UP, Decimal
+
+from travertino.size import at_least
 
 from toga.constants import CENTER, JUSTIFY, LEFT, RIGHT, TRANSPARENT
 
@@ -7,6 +10,7 @@
 from ..libs.android.graphics import PorterDuff__Mode, PorterDuffColorFilter, Rect
 from ..libs.android.graphics.drawable import ColorDrawable, InsetDrawable
 from ..libs.android.view import Gravity, View
+from ..libs.android.widget import RelativeLayout__LayoutParams
 
 
 def _get_activity(_cache=[]):
@@ -30,7 +34,30 @@ def _get_activity(_cache=[]):
     return _cache[0]
 
 
-class Widget:
+class Scalable:
+    SCALE_DEFAULT_ROUNDING = ROUND_HALF_EVEN
+
+    def init_scale(self, context):
+        # The baseline DPI is 160:
+        # https://developer.android.com/training/multiscreen/screendensities
+        self.scale = context.getResources().getDisplayMetrics().densityDpi / 160
+
+    # Convert CSS pixels to native pixels
+    def scale_in(self, value, rounding=SCALE_DEFAULT_ROUNDING):
+        return self.scale_round(value * self.scale, rounding)
+
+    # Convert native pixels to CSS pixels
+    def scale_out(self, value, rounding=SCALE_DEFAULT_ROUNDING):
+        if isinstance(value, at_least):
+            return at_least(self.scale_out(value.value, rounding))
+        else:
+            return self.scale_round(value / self.scale, rounding)
+
+    def scale_round(self, value, rounding):
+        return int(Decimal(value).to_integral(rounding))
+
+
+class Widget(ABC, Scalable):
     # Some widgets are not generally focusable, but become focusable if there has been a
     # keyboard event since the last touch event. To avoid this complicating the tests,
     # these widgets disable programmatic focus entirely by setting focusable = False.
@@ -43,7 +70,18 @@ def __init__(self, interface):
         self._container = None
         self.native = None
         self._native_activity = _get_activity()
+        self.init_scale(self._native_activity)
         self.create()
+
+        # Some widgets, e.g. TextView, may throw an exception if we call measure()
+        # before setting LayoutParams.
+        self.native.setLayoutParams(
+            RelativeLayout__LayoutParams(
+                RelativeLayout__LayoutParams.WRAP_CONTENT,
+                RelativeLayout__LayoutParams.WRAP_CONTENT,
+            )
+        )
+
         # Immediately re-apply styles. Some widgets may defer style application until
         # they have been added to a container.
         self.interface.style.reapply()
@@ -74,19 +112,7 @@ def container(self, container):
         for child in self.interface.children:
             child._impl.container = container
 
-        self.rehint()
-
-    @property
-    def viewport(self):
-        return self._container
-
-    # Convert CSS pixels to native pixels
-    def scale_in(self, value):
-        return int(round(value * self.container.scale))
-
-    # Convert native pixels to CSS pixels
-    def scale_out(self, value):
-        return int(round(value / self.container.scale))
+        self.refresh()
 
     def get_enabled(self):
         return self.native.isEnabled()
@@ -107,7 +133,9 @@ def set_tab_index(self, tab_index):
     # APPLICATOR
 
     def set_bounds(self, x, y, width, height):
-        self.container.set_content_bounds(self, x, y, width, height)
+        self.container.set_content_bounds(
+            self, *map(self.scale_in, (x, y, width, height))
+        )
 
     def set_hidden(self, hidden):
         if hidden:
@@ -170,12 +198,21 @@ def insert_child(self, index, child):
     def remove_child(self, child):
         child.container = None
 
+    # TODO: consider calling requestLayout or forceLayout here
+    # (https://github.com/beeware/toga/issues/1289#issuecomment-1453096034)
     def refresh(self):
+        intrinsic = self.interface.intrinsic
+        intrinsic.width = intrinsic.height = None
         self.rehint()
+        assert intrinsic.width is not None, self
+        assert intrinsic.height is not None, self
+
+        intrinsic.width = self.scale_out(intrinsic.width, ROUND_UP)
+        intrinsic.height = self.scale_out(intrinsic.height, ROUND_UP)
 
     @abstractmethod
     def rehint(self):
-        pass
+        ...
 
 
 def align(value):

android/src/toga_android/widgets/button.py

@@ -35,10 +35,6 @@ def set_background_color(self, value):
         self.set_background_filter(value)
 
     def rehint(self):
-        # Like other text-viewing widgets, Android crashes when rendering
-        # `Button` unless it has its layout params set. Guard for that case.
-        if not self.native.getLayoutParams():
-            return
         self.native.measure(
             View__MeasureSpec.UNSPECIFIED,
             View__MeasureSpec.UNSPECIFIED,

android/src/toga_android/widgets/canvas.py

@@ -1,5 +1,7 @@
 import math
 
+from travertino.size import at_least
+
 from ..libs import activity
 from ..libs.android.graphics import (
     DashPathEffect,
@@ -214,3 +216,7 @@ def get_image_data(self):
 
     def set_on_resize(self, handler):
         self.interface.factory.not_implemented("Canvas.on_resize")
+
+    def rehint(self):
+        self.interface.intrinsic.width = at_least(0)
+        self.interface.intrinsic.height = at_least(0)

android/src/toga_android/widgets/detailedlist.py

@@ -204,9 +204,6 @@ def scroll():
         Handler().post(PythonRunnable(scroll))
 
     def rehint(self):
-        # Android can crash when rendering some widgets until they have their layout params set. Guard for that case.
-        if not self.native.getLayoutParams():
-            return
         self.native.measure(
             View__MeasureSpec.UNSPECIFIED,
             View__MeasureSpec.UNSPECIFIED,

android/src/toga_android/widgets/internal/pickers.py

@@ -40,11 +40,6 @@ def create(self):
 
     def rehint(self):
         self.interface.intrinsic.width = at_least(300)
-        # Refuse to call measure() if widget has no container, i.e., has no LayoutParams.
-        # On Android, EditText's measure() throws NullPointerException if the widget has no
-        # LayoutParams.
-        if not self.native.getLayoutParams():
-            return
         self.native.measure(
             View__MeasureSpec.UNSPECIFIED, View__MeasureSpec.UNSPECIFIED
         )

android/src/toga_android/widgets/label.py

@@ -56,10 +56,6 @@ def set_text(self, value):
         self.native.setText(value)
 
     def rehint(self):
-        # Refuse to rehint an Android TextView if it has no LayoutParams yet.
-        # Calling measure() on an Android TextView w/o LayoutParams raises NullPointerException.
-        if not self.native.getLayoutParams():
-            return
         # Ask the Android TextView first for its minimum possible height.
         # This is the height with word-wrapping disabled.
         self.native.measure(

android/src/toga_android/widgets/progressbar.py

@@ -91,10 +91,6 @@ def set_value(self, value):
         self.native.setProgress(int(value * self.TOGA_SCALE))
 
     def rehint(self):
-        # Android can crash when rendering some widgets until
-        # they have their layout params set. Guard for that case.
-        if not self.native.getLayoutParams():
-            return
         self.native.measure(
             View__MeasureSpec.UNSPECIFIED,
             View__MeasureSpec.UNSPECIFIED,

android/src/toga_android/widgets/scrollcontainer.py

@@ -1,3 +1,5 @@
+from decimal import ROUND_DOWN
+
 from travertino.size import at_least
 
 from ..container import Container
@@ -65,7 +67,10 @@ def create(self):
 
     def set_bounds(self, x, y, width, height):
         super().set_bounds(x, y, width, height)
-        self.resize_content(width, height)
+        self.resize_content(
+            self.scale_in(width, ROUND_DOWN),
+            self.scale_in(height, ROUND_DOWN),
+        )
 
     def get_vertical(self):
         return self.vScrollListener.is_scrolling_enabled

android/src/toga_android/widgets/switch.py

@@ -44,8 +44,6 @@ def set_value(self, value):
         self.native.setChecked(bool(value))
 
     def rehint(self):
-        if not self.native.getLayoutParams():
-            return
         self.native.measure(
             View__MeasureSpec.UNSPECIFIED, View__MeasureSpec.UNSPECIFIED
         )

android/src/toga_android/widgets/table.py

@@ -229,11 +229,6 @@ def set_font(self, font):
             self.change_source(self.interface.data)
 
     def rehint(self):
-        # Android can crash when rendering some widgets until
-        # they have their layout params set. Guard for that case.
-        if not self.native.getLayoutParams():
-            return
-
         self.native.measure(
             View__MeasureSpec.UNSPECIFIED,
             View__MeasureSpec.UNSPECIFIED,

android/src/toga_android/widgets/textinput.py

@@ -118,11 +118,6 @@ def _on_lose_focus(self):
 
     def rehint(self):
         self.interface.intrinsic.width = at_least(self.interface._MIN_WIDTH)
-        # Refuse to call measure() if widget has no container, i.e., has no LayoutParams.
-        # On Android, EditText's measure() throws NullPointerException if the widget has no
-        # LayoutParams.
-        if not self.native.getLayoutParams():
-            return
         self.native.measure(
             View__MeasureSpec.UNSPECIFIED, View__MeasureSpec.UNSPECIFIED
         )

android/src/toga_android/window.py

@@ -1,3 +1,5 @@
+from decimal import ROUND_UP
+
 from .container import Container
 from .libs.android import R__id
 from .libs.android.view import ViewTreeObserver__OnGlobalLayoutListener
@@ -62,6 +64,20 @@ def hide(self):
         # A no-op, as the window cannot be hidden.
         pass
 
+    def refreshed(self):
+        if self.native_width and self.native_height:
+            layout = self.interface.content.layout
+            available_width = self.scale_out(self.native_width, ROUND_UP)
+            available_height = self.scale_out(self.native_height, ROUND_UP)
+            if (layout.width > available_width) or (layout.height > available_height):
+                # Show the sizes in terms of CSS pixels.
+                print(
+                    f"Warning: Window content {(layout.width, layout.height)} "
+                    f"exceeds available space {(available_width, available_height)}"
+                )
+
+        super().refreshed()
+
     def get_visible(self):
         # The window is always visible
         return True

changes/2020.bugfix.rst

@@ -0,0 +1 @@
+The minimum window size is now correctly recomputed and enforced if window content changes.