Add IconThemeData adjustment to ListTile trailing element (#11858)

* Add IconThemeData adjustment to ListTile trailing element (makes consistent with leading element)

* Add test for ListTile theme changes

* Pull out and share IconThemeData variable between leading and trailing

* remove extra comma

* fix style nit

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

@@ -387,9 +387,13 @@ class ListTile extends StatelessWidget {
     // Overall, the list tile is a Row() with these children.
     final List<Widget> children = <Widget>[];
 
+    IconThemeData iconThemeData;
+    if (leading != null || trailing != null)
+      iconThemeData = new IconThemeData(color: _iconColor(theme, tileTheme));
+
     if (leading != null) {
       children.add(IconTheme.merge(
-        data: new IconThemeData(color: _iconColor(theme, tileTheme)),
+        data: iconThemeData,
         child: new Container(
           margin: const EdgeInsetsDirectional.only(end: 16.0),
           width: 40.0,
@@ -424,10 +428,14 @@ class ListTile extends StatelessWidget {
     ));
 
     if (trailing != null) {
-      children.add(new Container(
+      children.add(IconTheme.merge(
+        data: iconThemeData,
+        child: new Container(
           margin: const EdgeInsetsDirectional.only(start: 16.0),
+          width: 40.0,
           alignment: FractionalOffsetDirectional.centerEnd,
           child: trailing,
+        ),
       ));
     }
 

packages/flutter/test/material/list_tile_test.dart

@@ -178,6 +178,8 @@ void main() {
   testWidgets('ListTileTheme', (WidgetTester tester) async {
     final Key titleKey = new UniqueKey();
     final Key subtitleKey = new UniqueKey();
+    final Key leadingKey = new UniqueKey();
+    final Key trailingKey = new UniqueKey();
     ThemeData theme;
 
     Widget buildFrame({
@@ -202,7 +204,8 @@ void main() {
                   return new ListTile(
                     enabled: enabled,
                     selected: selected,
-                    leading: const TestIcon(),
+                    leading: new TestIcon(key: leadingKey),
+                    trailing: new TestIcon(key: trailingKey),
                     title: new TestText('title', key: titleKey),
                     subtitle: new TestText('subtitle', key: subtitleKey),
                   );
@@ -217,35 +220,39 @@ void main() {
     const Color green = const Color(0xFF00FF00);
     const Color red = const Color(0xFFFF0000);
 
-    Color iconColor() => tester.state<TestIconState>(find.byType(TestIcon)).iconTheme.color;
+    Color iconColor(Key key) => tester.state<TestIconState>(find.byKey(key)).iconTheme.color;
     Color textColor(Key key) => tester.state<TestTextState>(find.byKey(key)).textStyle.color;
 
-    // A selected ListTile's leading and text get the primary color by default
+    // A selected ListTile's leading, trailing, and text get the primary color by default
     await(tester.pumpWidget(buildFrame(selected: true)));
     await(tester.pump(const Duration(milliseconds: 300))); // DefaultTextStyle changes animate
-    expect(iconColor(), theme.primaryColor);
+    expect(iconColor(leadingKey), theme.primaryColor);
+    expect(iconColor(trailingKey), theme.primaryColor);
     expect(textColor(titleKey), theme.primaryColor);
     expect(textColor(subtitleKey), theme.primaryColor);
 
-    // A selected ListTile's leading and text get the ListTileTheme's selectedColor
+    // A selected ListTile's leading, trailing, and text get the ListTileTheme's selectedColor
     await(tester.pumpWidget(buildFrame(selected: true, selectedColor: green)));
     await(tester.pump(const Duration(milliseconds: 300))); // DefaultTextStyle changes animate
-    expect(iconColor(), green);
+    expect(iconColor(leadingKey), green);
+    expect(iconColor(trailingKey), green);
     expect(textColor(titleKey), green);
     expect(textColor(subtitleKey), green);
 
-    // An unselected ListTile's leading icon gets the ListTileTheme's iconColor
+    // An unselected ListTile's leading and trailing get the ListTileTheme's iconColor
     // An unselected ListTile's title texts get the ListTileTheme's textColor
     await(tester.pumpWidget(buildFrame(iconColor: red, textColor: green)));
     await(tester.pump(const Duration(milliseconds: 300))); // DefaultTextStyle changes animate
-    expect(iconColor(), red);
+    expect(iconColor(leadingKey), red);
+    expect(iconColor(trailingKey), red);
     expect(textColor(titleKey), green);
     expect(textColor(subtitleKey), green);
 
     // If the item is disabled it's rendered with the theme's disabled color.
     await(tester.pumpWidget(buildFrame(enabled: false)));
     await(tester.pump(const Duration(milliseconds: 300)));  // DefaultTextStyle changes animate
-    expect(iconColor(), theme.disabledColor);
+    expect(iconColor(leadingKey), theme.disabledColor);
+    expect(iconColor(trailingKey), theme.disabledColor);
     expect(textColor(titleKey), theme.disabledColor);
     expect(textColor(subtitleKey), theme.disabledColor);
 
@@ -253,7 +260,8 @@ void main() {
     // Even if it's selected.
     await(tester.pumpWidget(buildFrame(enabled: false, selected: true)));
     await(tester.pump(const Duration(milliseconds: 300)));  // DefaultTextStyle changes animate
-    expect(iconColor(), theme.disabledColor);
+    expect(iconColor(leadingKey), theme.disabledColor);
+    expect(iconColor(trailingKey), theme.disabledColor);
     expect(textColor(titleKey), theme.disabledColor);
     expect(textColor(subtitleKey), theme.disabledColor);
   });