Why do Learn Async Programming?

Asynchronous operations make your program non-blocking. You call some async operations and your code it not waiting to complete the operation. Here are some common asynchronous operations:

  1. Fetching data over a network.
  2. Writing data to a database.
  3. Reading data from a file.

Async codes provides the result in form of Future or Stream.

Future example code

      const Duration(seconds: 2),
      () => 'Result after 2 sec',

Future has 2 States

  1. UnCompleted
  2. Completed - Completed can be with value or Completed with error.

Future with Completed Successfully completed state.

Future<String> fetchUserInfo() {
  return Future.delayed(const Duration(seconds: 5), () => "Amit Srivastava");

Future with Completed Error.

Future<void> fetchUserInfo() {
	return Future.delayed(const Duration(seconds: 5),
      () => throw Exception('No User Found...'));

The await  means Async Wait, It means function  executes asynchronously and, when it is done, continue on to the next line of code.

Note: you can't use await without async.

Generally it is recommened during login , register, payments where you need to wait till async code execute and then move to the next line.

Future<String> login(){
	return Future.delayed(const Duration(seconds: 5), ()=>"Login Done ");

void main() async{
	var r = await login();

Note : For Error Handling during await use try catch.

That's all Folks catch you in next tutorial.