[Material] Theme-able TextStyles for AlertDialog (#25339)

* Themable elevation on dialogs.

* AlertDialogs Title/Content text styles

* Themable elevation on dialogs.

AlertDialogs Title/Content text styles

* finish merging change

* fixing tests

* Docs fixes

* Change const to final to fix analyzer errors

* Fix analyzer errors

* Remove dart:ui import

* Hans Comments

packages/flutter/lib/src/material/dialog.dart

@@ -3,7 +3,6 @@
 // found in the LICENSE file.
 
 import 'dart:async';
-import 'dart:ui';
 
 import 'package:flutter/foundation.dart';
 import 'package:flutter/widgets.dart';
@@ -204,8 +203,10 @@ class AlertDialog extends StatelessWidget {
     Key key,
     this.title,
     this.titlePadding,
+    this.titleTextStyle,
     this.content,
     this.contentPadding = const EdgeInsets.fromLTRB(24.0, 20.0, 24.0, 24.0),
+    this.contentTextStyle,
     this.actions,
     this.backgroundColor,
     this.elevation,
@@ -232,6 +233,12 @@ class AlertDialog extends StatelessWidget {
   /// [actions].
   final EdgeInsetsGeometry titlePadding;
 
+  /// Style for the text in the [title] of this [AlertDialog].
+  ///
+  /// If null, [DialogTheme.titleTextStyle] is used, if that's null, defaults to
+  /// [ThemeData.textTheme.title].
+  final TextStyle titleTextStyle;
+
   /// The (optional) content of the dialog is displayed in the center of the
   /// dialog in a lighter font.
   ///
@@ -248,6 +255,12 @@ class AlertDialog extends StatelessWidget {
   /// to separate the content from the other edges of the dialog.
   final EdgeInsetsGeometry contentPadding;
 
+  /// Style for the text in the [content] of this [AlertDialog].
+  ///
+  /// If null, [DialogTheme.contentTextStyle] is used, if that's null, defaults
+  /// to [ThemeData.textTheme.subhead].
+  final TextStyle contentTextStyle;
+
   /// The (optional) set of actions that are displayed at the bottom of the
   /// dialog.
   ///
@@ -287,6 +300,8 @@ class AlertDialog extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     assert(debugCheckHasMaterialLocalizations(context));
+    final ThemeData theme = Theme.of(context);
+    final DialogTheme dialogTheme = DialogTheme.of(context);
     final List<Widget> children = <Widget>[];
     String label = semanticLabel;
 
@@ -294,7 +309,7 @@ class AlertDialog extends StatelessWidget {
       children.add(Padding(
         padding: titlePadding ?? EdgeInsets.fromLTRB(24.0, 24.0, 24.0, content == null ? 20.0 : 0.0),
         child: DefaultTextStyle(
-          style: Theme.of(context).textTheme.title,
+          style: titleTextStyle ?? dialogTheme.titleTextStyle ?? theme.textTheme.title,
           child: Semantics(child: title, namesRoute: true),
         ),
       ));
@@ -314,7 +329,7 @@ class AlertDialog extends StatelessWidget {
         child: Padding(
           padding: contentPadding,
           child: DefaultTextStyle(
-            style: Theme.of(context).textTheme.subhead,
+            style: contentTextStyle ?? dialogTheme.contentTextStyle ?? theme.textTheme.subhead,
             child: content,
           ),
         ),

packages/flutter/lib/src/material/dialog_theme.dart

@@ -18,6 +18,10 @@ import 'theme.dart';
 /// When Shape is `null`, the dialog defaults to a [RoundedRectangleBorder] with
 /// a border radius of 2.0 on all corners.
 ///
+/// [titleTextStyle] and [contentTextStyle] are used in [AlertDialogs].
+/// If null, they default to [ThemeData.textTheme.title] and [ThemeData.textTheme.subhead],
+/// respectively.
+///
 /// See also:
 ///
 ///  * [Dialog], a material dialog that can be customized using this [DialogTheme].
@@ -25,9 +29,18 @@ import 'theme.dart';
 ///    application.
 class DialogTheme extends Diagnosticable {
   /// Creates a dialog theme that can be used for [ThemeData.dialogTheme].
-  const DialogTheme({ this.backgroundColor, this.elevation, this.shape });
+  const DialogTheme({
+    this.backgroundColor,
+    this.elevation,
+    this.shape,
+    this.titleTextStyle,
+    this.contentTextStyle,
+  });
 
   /// Default value for [Dialog.backgroundColor].
+  ///
+  /// If null, [ThemeData.dialogBackgroundColor] is used, if that's null,
+  /// defaults to [Colors.white].
   final Color backgroundColor;
 
   /// Default value for [Dialog.elevation].
@@ -38,13 +51,31 @@ class DialogTheme extends Diagnosticable {
   /// Default value for [Dialog.shape].
   final ShapeBorder shape;
 
+  /// Used to configure the [DefaultTextStyle] for the [AlertDialog.title] widget.
+  ///
+  /// If null, defaults to [ThemeData.textTheme.title].
+  final TextStyle titleTextStyle;
+
+  /// Used to configure the [DefaultTextStyle] for the [AlertDialog.content] widget.
+  ///
+  /// If null, defaults to [ThemeData.textTheme.subhead].
+  final TextStyle contentTextStyle;
+
   /// Creates a copy of this object but with the given fields replaced with the
   /// new values.
-  DialogTheme copyWith({ Color backgroundColor, double elevation, ShapeBorder shape }) {
+  DialogTheme copyWith({
+    Color backgroundColor,
+    double elevation,
+    ShapeBorder shape,
+    TextStyle titleTextStyle,
+    TextStyle contentTextStyle,
+  }) {
     return DialogTheme(
       backgroundColor: backgroundColor ?? this.backgroundColor,
       elevation: elevation ?? this.elevation,
       shape: shape ?? this.shape,
+      titleTextStyle: titleTextStyle ?? this.titleTextStyle,
+      contentTextStyle: contentTextStyle ?? this.contentTextStyle,
     );
   }
 
@@ -64,6 +95,8 @@ class DialogTheme extends Diagnosticable {
       backgroundColor: Color.lerp(a?.backgroundColor, b?.backgroundColor, t),
       elevation: lerpDouble(a?.elevation, b?.elevation, t),
       shape: ShapeBorder.lerp(a?.shape, b?.shape, t),
+      titleTextStyle: TextStyle.lerp(a?.titleTextStyle, b?.titleTextStyle, t),
+      contentTextStyle: TextStyle.lerp(a?.contentTextStyle, b?.contentTextStyle, t)
     );
   }
 
@@ -79,7 +112,9 @@ class DialogTheme extends Diagnosticable {
     final DialogTheme typedOther = other;
     return typedOther.backgroundColor == backgroundColor
         && typedOther.elevation == elevation
-        && typedOther.shape == shape;
+        && typedOther.shape == shape
+        && typedOther.titleTextStyle == titleTextStyle
+        && typedOther.contentTextStyle == contentTextStyle;
   }
 
   @override
@@ -88,5 +123,7 @@ class DialogTheme extends Diagnosticable {
     properties.add(DiagnosticsProperty<Color>('backgroundColor', backgroundColor));
     properties.add(DiagnosticsProperty<ShapeBorder>('shape', shape, defaultValue: null));
     properties.add(DiagnosticsProperty<double>('elevation', elevation));
+    properties.add(DiagnosticsProperty<TextStyle>('titleTextStyle', titleTextStyle, defaultValue: null));
+    properties.add(DiagnosticsProperty<TextStyle>('contentTextStyle', contentTextStyle, defaultValue: null));
   }
 }

packages/flutter/test/material/dialog_test.dart

@@ -5,6 +5,7 @@
 import 'dart:ui';
 
 import 'package:flutter/material.dart';
+import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:matcher/matcher.dart';
 
@@ -39,6 +40,10 @@ Material _getMaterialFromDialog(WidgetTester tester) {
   return tester.widget<Material>(find.descendant(of: find.byType(AlertDialog), matching: find.byType(Material)));
 }
 
+RenderParagraph _getTextRenderObjectFromDialog(WidgetTester tester, String text) {
+  return tester.element<StatelessElement>(find.descendant(of: find.byType(AlertDialog), matching: find.text(text))).renderObject;
+}
+
 const ShapeBorder _defaultDialogShape = RoundedRectangleBorder(borderRadius: BorderRadius.all(Radius.circular(2.0)));
 
 void main() {
@@ -116,6 +121,40 @@ void main() {
     expect(materialWidget.elevation, customElevation);
   });
 
+  testWidgets('Custom Title Text Style', (WidgetTester tester) async {
+    const String titleText = 'Title';
+    const TextStyle titleTextStyle = TextStyle(color: Colors.pink);
+    const AlertDialog dialog = AlertDialog(
+      title: Text(titleText),
+      titleTextStyle: titleTextStyle,
+      actions: <Widget>[ ],
+    );
+    await tester.pumpWidget(_appWithAlertDialog(tester, dialog));
+
+    await tester.tap(find.text('X'));
+    await tester.pumpAndSettle();
+
+    final RenderParagraph title = _getTextRenderObjectFromDialog(tester, titleText);
+    expect(title.text.style, titleTextStyle);
+  });
+
+  testWidgets('Custom Content Text Style', (WidgetTester tester) async {
+    const String contentText = 'Content';
+    const TextStyle contentTextStyle = TextStyle(color: Colors.pink);
+    const AlertDialog dialog = AlertDialog(
+      content: Text(contentText),
+      contentTextStyle: contentTextStyle,
+      actions: <Widget>[ ],
+    );
+    await tester.pumpWidget(_appWithAlertDialog(tester, dialog));
+
+    await tester.tap(find.text('X'));
+    await tester.pumpAndSettle();
+
+    final RenderParagraph content = _getTextRenderObjectFromDialog(tester, contentText);
+    expect(content.text.style, contentTextStyle);
+  });
+
   testWidgets('Custom dialog shape', (WidgetTester tester) async {
     const RoundedRectangleBorder customBorder =
       RoundedRectangleBorder(borderRadius: BorderRadius.all(Radius.circular(16.0)));

packages/flutter/test/material/dialog_theme_test.dart

@@ -39,20 +39,28 @@ Material _getMaterialFromDialog(WidgetTester tester) {
   return tester.widget<Material>(find.descendant(of: find.byType(AlertDialog), matching: find.byType(Material)));
 }
 
+RenderParagraph _getTextRenderObjectFromDialog(WidgetTester tester, String text) {
+  return tester.element<StatelessElement>(find.descendant(of: find.byType(AlertDialog), matching: find.text(text))).renderObject;
+}
+
 void main() {
-  testWidgets('Dialog Theme implements debugFillDescription', (WidgetTester tester) async {
+  testWidgets('Dialog Theme implements debugFillProperties', (WidgetTester tester) async {
     final DiagnosticPropertiesBuilder builder = DiagnosticPropertiesBuilder();
     const DialogTheme(
       backgroundColor: Color(0xff123456),
       elevation: 8.0,
       shape: null,
+      titleTextStyle: TextStyle(color: Color(0xffffffff)),
+      contentTextStyle: TextStyle(color: Color(0xff000000))
     ).debugFillProperties(builder);
     final List<String> description = builder.properties
         .where((DiagnosticsNode n) => !n.isFiltered(DiagnosticLevel.info))
         .map((DiagnosticsNode n) => n.toString()).toList();
     expect(description, <String>[
       'backgroundColor: Color(0xff123456)',
-      'elevation: 8.0'
+      'elevation: 8.0',
+      'titleTextStyle: TextStyle(inherit: true, color: Color(0xffffffff))',
+      'contentTextStyle: TextStyle(inherit: true, color: Color(0xff000000))',
     ]);
   });
 
@@ -128,4 +136,106 @@ void main() {
       skip: !Platform.isLinux,
     );
   });
-}
+
+  testWidgets('Custom Title Text Style - Constructor Param', (WidgetTester tester) async {
+    const String titleText = 'Title';
+    const TextStyle titleTextStyle = TextStyle(color: Colors.pink);
+    const AlertDialog dialog = AlertDialog(
+      title: Text(titleText),
+      titleTextStyle: titleTextStyle,
+      actions: <Widget>[ ],
+    );
+
+    await tester.pumpWidget(_appWithAlertDialog(tester, dialog));
+    await tester.tap(find.text('X'));
+    await tester.pumpAndSettle();
+
+    final RenderParagraph title = _getTextRenderObjectFromDialog(tester, titleText);
+    expect(title.text.style, titleTextStyle);
+  });
+
+  testWidgets('Custom Title Text Style - Dialog Theme', (WidgetTester tester) async {
+    const String titleText = 'Title';
+    const TextStyle titleTextStyle = TextStyle(color: Colors.pink);
+    const AlertDialog dialog = AlertDialog(
+      title: Text(titleText),
+      actions: <Widget>[ ],
+    );
+    final ThemeData theme = ThemeData(dialogTheme: const DialogTheme(titleTextStyle: titleTextStyle));
+
+    await tester.pumpWidget(_appWithAlertDialog(tester, dialog, theme: theme));
+    await tester.tap(find.text('X'));
+    await tester.pumpAndSettle();
+
+    final RenderParagraph title = _getTextRenderObjectFromDialog(tester, titleText);
+    expect(title.text.style, titleTextStyle);
+  });
+
+  testWidgets('Custom Title Text Style - Theme', (WidgetTester tester) async {
+    const String titleText = 'Title';
+    const TextStyle titleTextStyle = TextStyle(color: Colors.pink);
+    const AlertDialog dialog = AlertDialog(
+      title: Text(titleText),
+      actions: <Widget>[ ],
+    );
+    final ThemeData theme = ThemeData(textTheme: const TextTheme(title: titleTextStyle));
+
+    await tester.pumpWidget(_appWithAlertDialog(tester, dialog, theme: theme));
+    await tester.tap(find.text('X'));
+    await tester.pumpAndSettle();
+
+    final RenderParagraph title = _getTextRenderObjectFromDialog(tester, titleText);
+    expect(title.text.style.color, titleTextStyle.color);
+  });
+
+  testWidgets('Custom Content Text Style - Constructor Param', (WidgetTester tester) async {
+    const String contentText = 'Content';
+    const TextStyle contentTextStyle = TextStyle(color: Colors.pink);
+    const AlertDialog dialog = AlertDialog(
+      content: Text(contentText),
+      contentTextStyle: contentTextStyle,
+      actions: <Widget>[ ],
+    );
+
+    await tester.pumpWidget(_appWithAlertDialog(tester, dialog));
+    await tester.tap(find.text('X'));
+    await tester.pumpAndSettle();
+
+    final RenderParagraph content = _getTextRenderObjectFromDialog(tester, contentText);
+    expect(content.text.style, contentTextStyle);
+  });
+
+  testWidgets('Custom Content Text Style - Dialog Theme', (WidgetTester tester) async {
+    const String contentText = 'Content';
+    const TextStyle contentTextStyle = TextStyle(color: Colors.pink);
+    const AlertDialog dialog = AlertDialog(
+      content: Text(contentText),
+      actions: <Widget>[ ],
+    );
+    final ThemeData theme = ThemeData(dialogTheme: const DialogTheme(contentTextStyle: contentTextStyle));
+
+    await tester.pumpWidget(_appWithAlertDialog(tester, dialog, theme: theme));
+    await tester.tap(find.text('X'));
+    await tester.pumpAndSettle();
+
+    final RenderParagraph content = _getTextRenderObjectFromDialog(tester, contentText);
+    expect(content.text.style, contentTextStyle);
+  });
+
+  testWidgets('Custom Content Text Style - Theme', (WidgetTester tester) async {
+    const String contentText = 'Content';
+    const TextStyle contentTextStyle = TextStyle(color: Colors.pink);
+    const AlertDialog dialog = AlertDialog(
+      content: Text(contentText),
+      actions: <Widget>[ ],
+    );
+    final ThemeData theme = ThemeData(textTheme: const TextTheme(subhead: contentTextStyle));
+
+    await tester.pumpWidget(_appWithAlertDialog(tester, dialog, theme: theme));
+    await tester.tap(find.text('X'));
+    await tester.pumpAndSettle();
+
+    final RenderParagraph content = _getTextRenderObjectFromDialog(tester, contentText);
+    expect(content.text.style.color, contentTextStyle.color);
+  });
+}
\ No newline at end of file