Cocoa ScrollContainer at 100%, including container rework.

cocoa/src/toga_cocoa/constraints.py

@@ -100,10 +100,9 @@ def container(self, value):
             self.container.native.addConstraint(self.height_constraint)
 
     def update(self, x, y, width, height):
-        if self.container:
-            # print(f"UPDATE CONSTRAINTS {self.widget} in {self.container} {width}x{height}@{x},{y}")
-            self.left_constraint.constant = x
-            self.top_constraint.constant = y
+        # print(f"UPDATE CONSTRAINTS {self.widget} in {self.container} {width}x{height}@{x},{y}")
+        self.left_constraint.constant = x
+        self.top_constraint.constant = y
 
-            self.width_constraint.constant = width
-            self.height_constraint.constant = height
+        self.width_constraint.constant = width
+        self.height_constraint.constant = height

cocoa/src/toga_cocoa/containers.py

@@ -0,0 +1,104 @@
+from rubicon.objc import objc_method
+
+from .libs import (
+    NSLayoutAttributeBottom,
+    NSLayoutAttributeLeft,
+    NSLayoutAttributeRight,
+    NSLayoutAttributeTop,
+    NSLayoutConstraint,
+    NSLayoutRelationGreaterThanOrEqual,
+    NSView,
+)
+
+
+class TogaView(NSView):
+    @objc_method
+    def isFlipped(self) -> bool:
+        # Default Cocoa coordinate frame is around the wrong way.
+        return True
+
+
+class BaseContainer:
+    def __init__(self, on_refresh=None):
+        self.on_refresh = on_refresh
+        # macOS always renders at 96dpi. Scaling is handled
+        # transparently at the level of the screen compositor.
+        self.dpi = 96
+        self.baseline_dpi = self.dpi
+
+    def refreshed(self):
+        if self.on_refresh:
+            self.on_refresh()
+
+
+class MinimumContainer(BaseContainer):
+    def __init__(self):
+        """A container for evaluating the minumum possible size for a layout"""
+        super().__init__()
+        self.width = 0
+        self.height = 0
+
+
+class Container(BaseContainer):
+    def __init__(
+        self,
+        min_width=100,
+        min_height=100,
+        layout_native=None,
+        on_refresh=None,
+    ):
+        """
+        :param min_width: The minimum width to enforce on the container
+        :param min_height: The minimum height to enforce on the container
+        :param layout_native: The native widget that should be used to provide
+            size hints to the layout. This will usually be the container widget
+            itself; however, for widgets like ScrollContainer where the layout
+            needs to be computed based on a different size to what will be
+            rendered, the source of the size can be different.
+        :param on_refresh: The callback to be notified when this container's
+            layout is refreshed.
+        """
+        super().__init__(on_refresh=on_refresh)
+        self.native = TogaView.alloc().init()
+        self.layout_native = self.native if layout_native is None else layout_native
+
+        # Enforce a minimum size based on the content size.
+        # This is enforcing the *minimum* size; the container might actually be
+        # bigger. If the window is resizable, using >= allows the window to
+        # be dragged larger; if not resizable, it enforces the smallest
+        # size that can be programmatically set on the window.
+        self._min_width_constraint = NSLayoutConstraint.constraintWithItem_attribute_relatedBy_toItem_attribute_multiplier_constant_(  # noqa: E501
+            self.native,
+            NSLayoutAttributeRight,
+            NSLayoutRelationGreaterThanOrEqual,
+            self.native,
+            NSLayoutAttributeLeft,
+            1.0,
+            min_width,
+        )
+        self.native.addConstraint(self._min_width_constraint)
+
+        self._min_height_constraint = NSLayoutConstraint.constraintWithItem_attribute_relatedBy_toItem_attribute_multiplier_constant_(  # noqa: E501
+            self.native,
+            NSLayoutAttributeBottom,
+            NSLayoutRelationGreaterThanOrEqual,
+            self.native,
+            NSLayoutAttributeTop,
+            1.0,
+            min_height,
+        )
+        self.native.addConstraint(self._min_height_constraint)
+
+    @property
+    def width(self):
+        return self.layout_native.frame.size.width
+
+    @property
+    def height(self):
+        return self.layout_native.frame.size.height
+
+    def set_min_width(self, width):
+        self._min_width_constraint.constant = width
+
+    def set_min_height(self, height):
+        self._min_height_constraint.constant = height

cocoa/src/toga_cocoa/libs/foundation.py

@@ -35,6 +35,11 @@
 NSNotification = ObjCClass("NSNotification")
 NSNotification.declare_property("object")
 
+######################################################################
+# NSRunLoop.h
+NSRunLoop = ObjCClass("NSRunLoop")
+NSRunLoop.declare_class_property("currentRunLoop")
+
 ######################################################################
 # NSURL.h
 NSURL = ObjCClass("NSURL")

cocoa/src/toga_cocoa/widgets/base.py

@@ -34,7 +34,7 @@ def container(self):
     @container.setter
     def container(self, container):
         if self.container:
-            assert container is None, f"Widget {self} already has a container"
+            assert container is None, f"{self} already has a container"
 
             # Existing container should be removed
             self.constraints.container = None
@@ -53,11 +53,7 @@ def container(self, container):
 
     @property
     def viewport(self):
-        return self._viewport
-
-    @viewport.setter
-    def viewport(self, viewport):
-        self._viewport = viewport
+        return self._container
 
     def get_enabled(self):
         return self.native.isEnabled
@@ -106,11 +102,7 @@ def set_tab_index(self, tab_index):
     # INTERFACE
 
     def add_child(self, child):
-        if self.viewport:
-            # we are the top level NSView
-            child.container = self
-        else:
-            child.container = self.container
+        child.container = self.container
 
     def insert_child(self, index, child):
         self.add_child(child)

cocoa/src/toga_cocoa/widgets/box.py

@@ -1,17 +1,10 @@
 from travertino.size import at_least
 
-from toga_cocoa.libs import NSView, objc_method
+from toga_cocoa.containers import TogaView
 
 from .base import Widget
 
 
-class TogaView(NSView):
-    @objc_method
-    def isFlipped(self) -> bool:
-        # Default Cocoa coordinate frame is around the wrong way.
-        return True
-
-
 class Box(Widget):
     def create(self):
         self.native = TogaView.alloc().init()

cocoa/src/toga_cocoa/widgets/optioncontainer.py

@@ -1,7 +1,8 @@
+from rubicon.objc import objc_method
 from travertino.size import at_least
 
-from toga_cocoa.libs import NSObject, NSTabView, NSTabViewItem, objc_method
-from toga_cocoa.window import CocoaViewport
+from toga_cocoa.containers import Container
+from toga_cocoa.libs import NSObject, NSTabView, NSTabViewItem
 
 from ..libs import objc_property
 from .base import Widget
@@ -52,20 +53,18 @@ def add_content(self, index, text, widget):
             text (str): The text for the option container
             widget: The widget or widget tree that belongs to the text.
         """
-        widget.viewport = CocoaViewport(widget.native)
-
-        for child in widget.interface.children:
-            child._impl.container = widget
+        container = Container()
+        widget.container = container
 
         item = NSTabViewItem.alloc().init()
         item.label = text
 
         # Turn the autoresizing mask on the widget widget
         # into constraints. This makes the widget fill the
         # available space inside the OptionContainer.
-        widget.native.translatesAutoresizingMaskIntoConstraints = True
+        container.native.translatesAutoresizingMaskIntoConstraints = True
 
-        item.view = widget.native
+        item.view = container.native
         self.native.insertTabViewItem(item, atIndex=index)
 
     def remove_content(self, index):

cocoa/src/toga_cocoa/widgets/scrollcontainer.py

@@ -1,17 +1,18 @@
 from rubicon.objc import SEL, objc_method, objc_property
 from travertino.size import at_least
 
+from toga_cocoa.containers import Container
 from toga_cocoa.libs import (
     NSColor,
     NSMakePoint,
     NSMakeRect,
     NSNoBorder,
     NSNotificationCenter,
+    NSRunLoop,
     NSScrollView,
     NSScrollViewDidEndLiveScrollNotification,
     NSScrollViewDidLiveScrollNotification,
 )
-from toga_cocoa.window import CocoaViewport
 
 from .base import Widget
 
@@ -22,14 +23,6 @@ class TogaScrollView(NSScrollView):
 
     @objc_method
     def didScroll_(self, note) -> None:
-        # print(
-        #     f"SCROLL frame={self.impl.native.frame.size.width}x{self.impl.native.frame.size.height}"
-        #     f" @ {self.impl.native.frame.origin.x}x{self.impl.native.frame.origin.y}, "
-        #     f"doc={self.impl.native.documentView.frame.size.width}x{self.impl.native.documentView.frame.size.height}"
-        #     f" @ {self.impl.native.documentView.frame.origin.x}x{self.impl.native.documentView.frame.origin.y}, "
-        #     f"content={self.impl.native.contentView.frame.size.width}x{self.impl.native.contentView.frame.size.height}"
-        #     f" @ {self.impl.native.contentView.frame.origin.x}x{self.impl.native.contentView.frame.origin.y}, "
-        # )
         self.interface.on_scroll(None)
 
 
@@ -43,8 +36,14 @@ def create(self):
         self.native.borderType = NSNoBorder
         self.native.backgroundColor = NSColor.windowBackgroundColor
 
-        self.native.translatesAutoresizingMaskIntoConstraints = False
-        self.native.autoresizesSubviews = True
+        # The container for the document bases its layout on the
+        # size of the content view. It can only exceed the size
+        # of the contentView if scrolling is enabled in that axis.
+        self.document_container = Container(
+            layout_native=self.native.contentView,
+            on_refresh=self.content_refreshed,
+        )
+        self.native.documentView = self.document_container.native
 
         NSNotificationCenter.defaultCenter.addObserver(
             self.native,
@@ -63,26 +62,36 @@ def create(self):
         self.add_constraints()
 
     def set_content(self, widget):
-        if widget:
-            self.native.documentView = widget._impl.native
-            widget._impl.viewport = CocoaViewport(self.native.documentView)
+        # If there's existing content, clear its container
+        if self.interface.content:
+            self.interface.content._impl.container = None
 
-            for child in widget.children:
-                child._impl.container = widget._impl
-        else:
-            self.native.documentView = None
+        # If there's new content, set the container of the content
+        if widget:
+            widget.container = self.document_container
 
     def set_bounds(self, x, y, width, height):
-        # print("SET BOUNDS", x, y, width, height)
         super().set_bounds(x, y, width, height)
-        # Restrict dimensions of content to dimensions of ScrollContainer
-        # along any non-scrolling directions. Set dimensions of content
-        # to its layout dimensions along the scrolling directions.
+
+        # Setting the bounds changes the constraints, but that doesn't mean
+        # the constraints have been fully applied. Let the NSRunLoop tick once
+        # to ensure constraints are applied.
+        NSRunLoop.currentRunLoop.runUntilDate(None)
+
+        # Now that we have an updated size for the ScrollContainer, re-evaluate
+        # the size of the document content
+        if self.interface._content:
+            self.interface._content.refresh()
+
+    def content_refreshed(self):
+        width = self.native.frame.size.width
+        height = self.native.frame.size.height
+
         if self.interface.horizontal:
-            width = self.interface.content.layout.width
+            width = max(self.interface.content.layout.width, width)
 
         if self.interface.vertical:
-            height = self.interface.content.layout.height
+            height = max(self.interface.content.layout.height, height)
 
         self.native.documentView.frame = NSMakeRect(0, 0, width, height)
 

cocoa/src/toga_cocoa/widgets/splitcontainer.py

@@ -1,9 +1,9 @@
+from rubicon.objc import objc_method, objc_property
 from travertino.size import at_least
 
-from toga_cocoa.libs import NSObject, NSSize, NSSplitView, objc_method
-from toga_cocoa.window import CocoaViewport
+from toga_cocoa.containers import Container
+from toga_cocoa.libs import NSObject, NSSize, NSSplitView
 
-from ..libs import objc_property
 from .base import Widget
 
 
@@ -64,17 +64,15 @@ def create(self):
 
     def add_content(self, position, widget, flex):
         # TODO: add flex option to the implementation
-        widget.viewport = CocoaViewport(widget.native)
-
-        for child in widget.interface.children:
-            child._impl.container = widget
+        container = Container()
+        widget.container = container
 
         # Turn the autoresizing mask on the widget into constraints.
         # This makes the widget fill the available space inside the
         # SplitContainer.
         # FIXME Use Constraints to enforce min width and height of the widgets otherwise width of 0 is possible.
-        widget.native.translatesAutoresizingMaskIntoConstraints = True
-        self.native.addSubview(widget.native)
+        container.native.translatesAutoresizingMaskIntoConstraints = True
+        self.native.addSubview(container.native)
 
     def set_direction(self, value):
         self.native.vertical = value