Implement InheritedWidget

@@ -4,6 +4,7 @@
 
 - Implement InlineSpan and WidgetSpan
 - Fix Theme.withFont factory
+- Implement InheritedWidget
 
 ## 1.3.17
 

@@ -16,6 +16,7 @@
 
 library widget;
 
+import 'dart:collection';
 import 'dart:math' as math;
 import 'dart:typed_data';
 

@@ -158,13 +158,11 @@ class Page {
             maxHeight: pageFormat.height - _margin.vertical);
 
     final Theme calculatedTheme = theme ?? document.theme ?? Theme.base();
-    final Map<Type, Inherited> inherited = <Type, Inherited>{};
-    inherited[calculatedTheme.runtimeType] = calculatedTheme;
     final Context context = Context(
       document: document.document,
       page: _pdfPage,
       canvas: canvas,
-        inherited: inherited);
+    ).inheritFrom(calculatedTheme);
     if (_build != null) {
       final Widget child = _build(context);
       layout(child, context, constraints);

@@ -113,15 +113,13 @@ class MultiPage extends Page {
             ? (pageFormat.height - _margin.vertical)
             : (pageFormat.width - _margin.horizontal));
     final Theme calculatedTheme = theme ?? document.theme ?? Theme.base();
-    final Map<Type, Inherited> inherited = <Type, Inherited>{};
-    inherited[calculatedTheme.runtimeType] = calculatedTheme;
     Context context;
     double offsetEnd;
     double offsetStart;
     int index = 0;
     int sameCount = 0;
     final Context baseContext =
-        Context(document: document.document, inherited: inherited);
+        Context(document: document.document).inheritFrom(calculatedTheme);
     final List<Widget> children = _buildList(baseContext);
     WidgetContext widgetContext;
 

@@ -18,7 +18,19 @@ part of widget;
 
 @immutable
 class Context {
-  const Context({
+  factory Context({
+    @required PdfDocument document,
+    PdfPage page,
+    PdfGraphics canvas,
+  }) =>
+      Context._(
+        document: document,
+        page: page,
+        canvas: canvas,
+        inherited: HashMap<Type, Inherited>(),
+      );
+
+  const Context._({
     @required this.document,
     this.page,
     this.canvas,
@@ -30,7 +42,7 @@ class Context {
 
   final PdfGraphics canvas;
 
-  final Map<Type, Inherited> inherited;
+  final HashMap<Type, Inherited> inherited;
 
   final PdfDocument document;
 
@@ -45,8 +57,8 @@ class Context {
       {PdfPage page,
       PdfGraphics canvas,
       Matrix4 ctm,
-      Map<Type, Inherited> inherited}) {
-    return Context(
+      HashMap<Type, Inherited> inherited}) {
+    return Context._(
         document: document,
         page: page ?? this.page,
         canvas: canvas ?? this.canvas,
@@ -54,7 +66,8 @@ class Context {
   }
 
   Context inheritFrom(Inherited object) {
-    final Map<Type, Inherited> inherited = this.inherited;
+    final HashMap<Type, Inherited> inherited =
+        HashMap<Type, Inherited>.of(this.inherited);
     inherited[object.runtimeType] = object;
     return copyWith(inherited: inherited);
   }
@@ -172,3 +185,53 @@ abstract class MultiChildWidget extends Widget {
 
   final List<Widget> children;
 }
+
+class InheritedWidget extends Widget {
+  InheritedWidget({this.build, this.inherited});
+
+  final BuildCallback build;
+
+  final Inherited inherited;
+
+  Context _context;
+
+  Widget _child;
+
+  @override
+  void layout(Context context, BoxConstraints constraints,
+      {bool parentUsesSize = false}) {
+    if (_context == null) {
+      // final Inherited inherited = build(context);
+      if (inherited != null) {
+        _context = context.inheritFrom(inherited);
+      }
+    }
+
+    _context ??= context;
+    _child ??= build(_context);
+
+    if (_child != null) {
+      _child.layout(_context, constraints, parentUsesSize: parentUsesSize);
+      assert(_child.box != null);
+      box = _child.box;
+    } else {
+      box = PdfRect.fromPoints(PdfPoint.zero, constraints.smallest);
+    }
+  }
+
+  @override
+  void paint(Context context) {
+    assert(_context != null);
+    super.paint(_context);
+
+    if (_child != null) {
+      final Matrix4 mat = Matrix4.identity();
+      mat.translate(box.x, box.y);
+      context.canvas
+        ..saveContext()
+        ..setTransform(mat);
+      _child.paint(_context);
+      context.canvas.restoreContext();
+    }
+  }
+}

@@ -70,6 +70,53 @@ void main() {
     ));
   });
 
+  test('Theme Page 1', () {
+    final Theme theme = Theme.withFont(base: roboto);
+
+    pdf.addPage(Page(
+      theme: theme,
+      build: (Context context) => Center(
+        child: Text('Hello'),
+      ),
+    ));
+  });
+
+  test('Theme Page 2', () {
+    final Theme theme = Theme.base().copyWith(
+      tableHeader: TextStyle(font: openSansBold),
+      tableCell: TextStyle(font: roboto),
+    );
+
+    pdf.addPage(Page(
+      theme: theme,
+      build: (Context context) => Center(
+        child: Table.fromTextArray(context: context, data: [
+          ['Header', '123'],
+          ['Cell', '456']
+        ]),
+      ),
+    ));
+  });
+
+  test('Theme Page 3', () {
+    pdf.addPage(Page(
+      build: (Context context) => Center(
+        child: Column(
+          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
+          children: <Widget>[
+            Text('Hello default'),
+            InheritedWidget(
+              inherited: Theme.withFont(
+                base: roboto,
+              ),
+              build: (Context context) => Text('Hello themed'),
+            ),
+          ],
+        ),
+      ),
+    ));
+  });
+
   tearDownAll(() {
     final File file = File('widgets-theme.pdf');
     file.writeAsBytesSync(pdf.save());