Setting icon color to first ListTile in ExpansionTile. Fixes #23053

[jmolins]

In issue #23053, developer reports being unable to set the trailing icon color in the first ListTile of the ExpansionTile.

This behaviour can be seen in the Gallery app. Go to Material > Expand/collapse list control. The trailing arrow does not get the same blue color the title gets.

The problem is the following:

The ExpansionTile sets an IconThemeData before creating the ListTile and sets the color to be used forward. This is the original code:

        children: <Widget>[
          IconTheme.merge(
            data: IconThemeData(color: _iconColor.value),
            child: ListTile(
              onTap: _handleTap,
              leading: widget.leading,
              title: DefaultTextStyle(
                style: Theme.of(context).textTheme.subhead.copyWith(color: titleColor),
                child: widget.title,
              ),
              trailing: widget.trailing ?? RotationTransition(
                turns: _iconTurns,
                child: const Icon(Icons.expand_more),
              ),
            ),
          ),
          ClipRect(
            child: Align(
              heightFactor: _heightFactor.value,
              child: child,
            ),
          ),
        ],

The problem with this code is that the ListTile itself creates another IconThemeData in its build() method. And this new IconThemeData does not take into account the one created outside in the ExpansionTile.

This PR substitutes the IconThemeData by a ListTileTheme that is used natively by the code inside the ListTile to set its style.

Since the ListTileTheme can also provide a text style, it is used to provide the style for the title so it is no longer necessary to create a DefaultTextStyle, that is also removed from the code.

[Hixie]

This looks pretty reasonable.

Can you add a test to make sure we don't accidentally revert this?

[jmolins]

@Hixie, I have added the test as requested.

The test is based on the tests done for ListTile in

flutter/packages/flutter/test/material/list_tile_test.dart

Line 251 in db9fe3f

testWidgets('ListTileTheme', (WidgetTester tester) async {

.

In this case, though, since the ListTileTheme is just above the first ListTile, the tests apply only to this one. The test ensure that the theme in scope is correctly applied to the tile through the ListTileTheme.

[Hixie]

[Hixie]

Thanks for your contribution! I'll land it when the bots go green.

[HansMuller]

Landing this now (finally!).