how to add icon in the app bar in flutter

AppBar(  title: Text("Hello Appbar"),  leading: GestureDetector(      onTap: () { /* Write listener code here */ },      child: Icon(        Icons.menu,  // add custom icons also      ),  ),  actions: <Widget>[    Padding(      padding: EdgeInsets.only(right: 20.0),      child: GestureDetector(        onTap: () {},        child: Icon(          Icons.search,          size: 26.0,        ),      )    ),    Padding(      padding: EdgeInsets.only(right: 20.0),      child: GestureDetector(        onTap: () {},        child: Icon(            Icons.more_vert        ),      )    ),  ],),

AppBar(  title: Text("Hello Appbar"),  leading: Icon(    Icons.menu,  ),);