Lost and Found page

lost_and_found.dart

import "package:flutter_web/material.dart";
import "package:flutter_web/cupertino.dart";
import "package:flutter_web_ui/ui.dart" as ui;

// Lines like these are comments (only read by people, ignored by computer)
/// Lines like these (three slashes) explain only the class/function/variable right underneath them

// Any part of a comment in [brackets] are either defined here in this file or 
// can be searched for at https://api.flutter.dev

/// This is a [StatefulWidget]. The gist is that this widget can keep track of variables (ie, "state"), 
/// and change how it looks when those variables change. 
///
/// Here, we will use a variable to keep track of whether the tile is open or not.
class Tile extends StatefulWidget {
	
	/// This method (method = function belonging to an object -- in this case, [StatefulWidget]s) tells Flutter
	/// how to understand the state (variables) of this widget
	///
	/// We define [TileState] later. 
	@override
  TileState createState() => TileState();
}

/// This is a State object. State objects connect state (variables) to a Widget. 
/// All state objects need to extend [State] and refer to the widget they control.
class TileState extends State<Tile> {
	/// Whether this [Tile] should be open or not. 
	/// Starts off closed. 
  bool open = false;
 
	/// This method tells Flutter how the widget should look. This is identical to the build
	/// method of [StatelessWidget], except here we can use the [setState] method of [StatefulWidget]
	/// to tell Flutter we are changing the state of the widget, and the widget will reload 
	/// itself with the new values.
  @override
  Widget build(BuildContext context) => ExpansionPanelList(  // list of [ExpansionPanel]s. 
		children: [
			ExpansionPanel(  // a panel that can open and close
				isExpanded: open,  // whether it is opened or not. Can be changed by changing [open].
				headerBuilder: (_, __) => ListTile(  // generic layout Widget -- really helpful
					title: Text("Lost"),
					leading: IconButton(
						icon: Icon(Icons.add),
						// change [open] to its opposite (!open = "opposite of [open]")
						// uses [setState] to tell Flutter to reload the widget. 
						onPressed: () => setState(() => open = !open)
					),
				),
				body: ListTile(  //  body is the thing that expands
					title: Text("Hello")
				)
			),
		]
  );
}

void main() async {
	// This function needs to be called on WEB only!
  await ui.webOnlyInitializePlatform();
	// Actually run the app
  runApp(
		MaterialApp(
			home: Scaffold(
				appBar: AppBar(title: Text("Lost and found")),
				body: ListView(  // scrollable list
					children: [  // elements of the list
						Tile()  // an expanding [Tile], as defined above
					]
				)
			)
		)
  );
}