Dart's event loop supports most types of asynchronous operations through futures and streams, but those two alone cannot handle every scenario.

For advanced control of futures, reach for a completer.

To start, import dart-async, create a new completer, and give it a type.

The point of a completer is to access its future attribute, which you can programmatically resolve using the complete method.

One common use case for completers is any class which must complete asynchronous setup before completing its primary task.

To start, define a class which initializes a completer.

This one uses a bool to indicate whether the initialization was successful.

Next, add a getter to expose the completer's future.

Now, run your initialization code.

Then, complete your completer and pass a value that matches your type.

Any code that uses this class can now await isReady before calling methods that depend on that setup.

And if an instance of my class has already completed its initialization, isReady will resolve immediately.

Another fun use case for completers is abstracting away streams.

Imagine a class with an input stream and an output stream, and a method that needs to put one value into the input stream and then return the next value that is emitted from the output stream.

The only problem with streams is you don't know when that will happen.

Set up a completer in your method and immediately return its future.

Then, in your listener to the output stream, complete the completer.

This will send that new value through the future returned by the increment method.

Check the DartPad link in the video description for example code, or for more info on completers and all other Flutter development techniques, head to flutter.dev.

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