title: Why i can't use appbartheme to define the title in AppBar class
body: <p>I want to set the appbarTheme for the Appbar but i can't.</p>
  <p>Here is my appbarTheme</p>
  <pre><code>  Widget build(BuildContext context) {
      return MaterialApp(
        title: 'Helo mu baby',
        theme: ThemeData(
          primarySwatch: Colors.green,
          //Some Widget will use accentColor first and use primarySwatch like insure
          accentColor: Colors.amber,
          textTheme: ThemeData.light().textTheme.copyWith(
                 titleLarge: TextStyle(
                    fontFamily: 'OpenSans',
                    fontSize: 18,
                    fontWeight: FontWeight.bold,
                  ),
          ),
          fontFamily: &quot;QuickSand&quot;,
          appBarTheme: AppBarTheme(
            textTheme: ThemeData.light().textTheme.copyWith(
                  titleLarge: TextStyle(
                    color: Colors.indigo,
                    fontFamily: 'OpenSans',
                    fontSize: 45,
                    fontWeight: FontWeight.bold,
                  ),
                ),
          ),
        ),
        home: MyHomeApp(),
      );
    }
  }
  </code></pre>
  <p>Here is my AppBar and i use &quot;titleTextStyle: Theme.of(context).appBarTheme.titleTextStyle&quot; to define the theme but it is not correct.</p>
  <pre><code> Widget build(BuildContext context) {
      return Scaffold(  
        appBar: AppBar(
       titleTextStyle: Theme.of(context).appBarTheme.titleTextStyle,
          //100px
          title: Text(&quot;Helo mu baby&quot;),
          actions: [
            IconButton(
                onPressed: (() {
                  _startAddNewTransaction(context);
                }),
                icon: Icon(Icons.add))
          ],
        ),
  
  </code></pre>