Futures trong Dart

Future<String> fetchData() {
  return Future.delayed(
    Duration(seconds: 2),
    () => 'Data loaded!',
  );
}
 
void main() {
  print('Start');
  fetchData().then((data) {
    print(data);
  });
  print('End');
}
// Output: Start, End, Data loaded!

Future<String> fetchData() async {
  await Future.delayed(Duration(seconds: 2));
  return 'Data loaded!';
}
 
Future<void> main() async {
  print('Start');
  String data = await fetchData();
  print(data);
  print('End');
}
// Output: Start, Data loaded!, End

Future<String> fetchData() async {
  await Future.delayed(Duration(seconds: 1));
  throw Exception('Network error');
}
 
// Với then/catchError
void example1() {
  fetchData()
    .then((data) => print(data))
    .catchError((error) => print('Error: $error'));
}
 
// Với try/catch
Future<void> example2() async {
  try {
    var data = await fetchData();
    print(data);
  } catch (e) {
    print('Error: $e');
  }
}

Future<int> getValue() {
  return Future.value(42);  // Resolved immediately
}
 
Future<int> getError() {
  return Future.error('Something went wrong');
}

Future<void> main() async {
  var results = await Future.wait([
    fetchUser(),
    fetchPosts(),
    fetchComments(),
  ]);
  
  print('User: ${results[0]}');
  print('Posts: ${results[1]}');
  print('Comments: ${results[2]}');
}

Future<String> server1() async {
  await Future.delayed(Duration(seconds: 3));
  return 'Server 1';
}
 
Future<String> server2() async {
  await Future.delayed(Duration(seconds: 1));
  return 'Server 2';
}
 
Future<void> main() async {
  var fastest = await Future.any([server1(), server2()]);
  print(fastest);  // Server 2
}

Future<void> main() async {
  await fetchData()
    .then((data) => print('Success: $data'))
    .catchError((e) => print('Error: $e'))
    .whenComplete(() => print('Done!'));
}

Future<void> main() async {
  try {
    var result = await fetchData()
        .timeout(Duration(seconds: 5));
    print(result);
  } on TimeoutException {
    print('Request timed out');
  }
}

FutureBuilder<String>(
  future: fetchData(),
  builder: (context, snapshot) {
    if (snapshot.connectionState == ConnectionState.waiting) {
      return CircularProgressIndicator();
    }
    if (snapshot.hasError) {
      return Text('Error: ${snapshot.error}');
    }
    return Text('Data: ${snapshot.data}');
  },
)