[flutter_markdown] Pass parent TextStyle down to MarkdownElementBuilder.visitElementAfter

packages/flutter_markdown/CHANGELOG.md

@@ -1,5 +1,9 @@
-## NEXT
+## 0.6.15
 
+* Introduce a new `MarkdownElementBuilder.visitElementAfterWithContext()` method passing the widget `BuildContext` and
+  the parent texts' `TextStyle`.  
+  This should allow custom syntax implementations to get data from the current context, as well as properly style any
+  text, e.g. a color syntax can make parts of a headline colored, while still keeping the font size of the headline.
 * Aligns Dart and Flutter SDK constraints.
 
 ## 0.6.14

packages/flutter_markdown/lib/src/builder.dart

@@ -74,6 +74,13 @@ class _InlineElement {
 
 /// A delegate used by [MarkdownBuilder] to control the widgets it creates.
 abstract class MarkdownBuilderDelegate {
+  /// Returns the [BuildContext] of the [MarkdownWidget].
+  ///
+  /// The context will be passed down to the
+  /// [MarkdownElementBuilder.visitElementBefore] method and allows elements to
+  /// get information from the context.
+  BuildContext get context;
+
   /// Returns a gesture recognizer to use for an `a` element with the given
   /// text, `href` attribute, and title.
   GestureRecognizer createLink(String text, String? href, String title);
@@ -451,8 +458,12 @@ class MarkdownBuilder implements md.NodeVisitor {
       }
 
       if (builders.containsKey(tag)) {
-        final Widget? child =
-            builders[tag]!.visitElementAfter(element, styleSheet.styles[tag]);
+        final Widget? child = builders[tag]!.visitElementAfterWithContext(
+          delegate.context,
+          element,
+          styleSheet.styles[tag],
+          parent.style,
+        );
         if (child != null) {
           current.children[0] = child;
         }

packages/flutter_markdown/lib/src/widget.dart

@@ -70,13 +70,33 @@ abstract class MarkdownElementBuilder {
   /// If you needn't build a widget, return null.
   Widget? visitText(md.Text text, TextStyle? preferredStyle) => null;
 
+  /// Called when an Element has been reached, after its children have been
+  /// visited.
+  ///
+  /// If [MarkdownWidget.styleSheet] has a style of this tag, will passing
+  /// to [preferredStyle].
+  ///
+  /// If parent element has [TextStyle]'s set, it will be passed as
+  /// [parentStyle].
+  ///
+  /// If you needn't build a widget, return null.
+  Widget? visitElementAfterWithContext(
+    BuildContext context,
+    md.Element element,
+    TextStyle? preferredStyle,
+    TextStyle? parentStyle,
+  ) {
+    return visitElementAfter(element, preferredStyle);
+  }
+
   /// Called when an Element has been reached, after its children have been
   /// visited.
   ///
   /// If [MarkdownWidget.styleSheet] has a style of this tag, will passing
   /// to [preferredStyle].
   ///
   /// If you needn't build a widget, return null.
+  @Deprecated('Use visitElementAfterWithContext() instead.')
   Widget? visitElementAfter(md.Element element, TextStyle? preferredStyle) =>
       null;
 }

packages/flutter_markdown/pubspec.yaml

@@ -4,7 +4,7 @@ description: A Markdown renderer for Flutter. Create rich text output,
   formatted with simple Markdown tags.
 repository: https://github.com/flutter/packages/tree/main/packages/flutter_markdown
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+flutter_markdown%22
-version: 0.6.14
+version: 0.6.15
 
 environment:
   sdk: ">=2.17.0 <3.0.0"

packages/flutter_markdown/test/custom_syntax_test.dart

@@ -3,7 +3,7 @@
 // found in the LICENSE file.
 
 import 'package:flutter/gestures.dart';
-import 'package:flutter/widgets.dart';
+import 'package:flutter/material.dart';
 import 'package:flutter_markdown/flutter_markdown.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:markdown/markdown.dart' as md;
@@ -83,6 +83,34 @@ void defineTests() {
         expect(widgetSpan.child, isInstanceOf<Container>());
       },
     );
+
+    testWidgets(
+      'visitElementAfterWithContext is handled correctly',
+      (WidgetTester tester) async {
+        await tester.pumpWidget(
+          boilerplate(
+            Markdown(
+              data: r'# This is a header with some \color1{color} in it',
+              extensionSet: md.ExtensionSet.none,
+              inlineSyntaxes: <md.InlineSyntax>[InlineTextColorSyntax()],
+              builders: <String, MarkdownElementBuilder>{
+                'inlineTextColor': InlineTextColorElementBuilder(),
+              },
+            ),
+          ),
+        );
+
+        final RichText textWidget = tester.widget(find.byType(RichText));
+        final TextSpan rootSpan = textWidget.text as TextSpan;
+        final TextSpan firstSpan = rootSpan.children![0] as TextSpan;
+        final TextSpan secondSpan = rootSpan.children![1] as TextSpan;
+        final TextSpan thirdSpan = rootSpan.children![2] as TextSpan;
+
+        expect(secondSpan.style!.color, Colors.red);
+        expect(secondSpan.style!.fontSize, firstSpan.style!.fontSize);
+        expect(secondSpan.style!.fontSize, thirdSpan.style!.fontSize);
+      },
+    );
   });
 
   testWidgets(
@@ -225,3 +253,54 @@ class ContainerBuilder2 extends MarkdownElementBuilder {
     );
   }
 }
+
+// Note: The implementation of inline span is incomplete, it does not handle
+// bold, italic, ... text with a colored block.
+// This would not work: `\color1{Text with *bold* text}`
+class InlineTextColorSyntax extends md.InlineSyntax {
+  InlineTextColorSyntax() : super(r'\\color([1-9]){(.*?)}');
+
+  @override
+  bool onMatch(md.InlineParser parser, Match match) {
+    final String colorId = match.group(1)!;
+    final String textContent = match.group(2)!;
+    final md.Element node = md.Element.text(
+      'inlineTextColor',
+      textContent,
+    )..attributes['color'] = colorId;
+
+    parser.addNode(node);
+
+    parser.addNode(
+      md.Text(''),
+    );
+    return true;
+  }
+}
+
+class InlineTextColorElementBuilder extends MarkdownElementBuilder {
+  @override
+  Widget visitElementAfterWithContext(
+      BuildContext context,
+      md.Element element,
+      TextStyle? preferredStyle,
+      TextStyle? parentStyle,
+      ) {
+    final String innerText = element.textContent;
+    final String color = element.attributes['color'] ?? '';
+
+    final Map<String, Color> contentColors = <String, Color>{
+      '1': Colors.red,
+      '2': Colors.green,
+      '3': Colors.blue,
+    };
+    final Color? contentColor = contentColors[color];
+
+    return RichText(
+      text: TextSpan(
+        text: innerText,
+        style: parentStyle?.copyWith(color: contentColor),
+      ),
+    );
+  }
+}