dart_command 1.1.0

Package to create commands for command pattern

Command

dart_command is a package that will help you to create commands according to Command Pattern as described on The command pattern.

With this package you'll can use command on ListenableBuilder (ChangeNotifier) as well StreamBuilder (Streams).

Usage

We have basicly two ways to use Command. First as inheritance:

class CounterCommand extends Command<int> {
  CounterCommand(super.value);

  @override
  void validate(int currentValue) {
    if (currentValue >= 10) {
      throw 'Value can\'t be more than 10';
    }
  }

  @override
  Future<int> action(currentValue) async {
    final incrrementedValue = currentValue + 1;
    return incrrementedValue;
  }
}

copied to clipboard

And we'll can instantiate like this:

final _counterCommand = CounterCommand(0);

copied to clipboard

And another way by factory:

final _randomNumberCommand = Command.crerate(
    value: 0,
    action: (_) async {
        return Random().nextInt(100);
    },
);

copied to clipboard

Command have a closure called action. This is where you'll do your logic and return te result to command.

Validate

One of the methods you can override is validate(currentValue). It passes the current value and you just do logical validations inside it.

@override
void validate(int currentValue) {
    if (currentValue >= 10) {
        throw 'Value can\'t be more than 10';
    }
}

copied to clipboard

Action

action(currentValue) is the method that'll called when execute() is called. Inside it you must have to put what you want to execute after validate.

@override
Future<int> action(currentValue) async {
    final incrementedValue = currentValue + 1;
    return incrementedValue;
}

copied to clipboard

ListenableBuilder and StreamBuilder

Now you just passa these commands to ListenableBuilder or StreamBuilder.

ListenableBuilder and ValueListenableBuilder usage:

ListenableBuilder(
    listenable: _counterCommand,
    builder: (context, child) {
        return Text(
            'Counte Command as Listenable (ChangeNotify) = ${_counterCommand.value}',
            style: Theme.of(context).textTheme.headlineMedium,
        );
    },
)

copied to clipboard

or

ValueListenableBuilder(
    valueListenable: _counterCommand,
    builder: (context, i, child) {
        return Text(
            'Counte Command as ValueListenable (ChangeNotify) = ${_counterCommand.value}',
            style: Theme.of(context).textTheme.headlineMedium,
        );
    },
),

copied to clipboard

StreamBuilder usage:

StreamBuilder<int>(
    stream: _randomNumberCommand,
    builder: (context, snapshot) {
        return Text(
            'Random number Command as Stream = ${snapshot.data}',
            style: Theme.of(context).textTheme.headlineMedium,
        );
    },
)

copied to clipboard

State

Every command have a state. For every moment that the command is, one state will be. To get state just Command.state

    Created
    Running
    Error
    Completed

copied to clipboard

Value and Error

At any time you can get a value or error from command. To get value just Command.value and for the error do Command.errorWrapper.

The ErrorWrapper have Object with error and the stackTrace.

Execute a command

For the last but not least. To execute the command just call Command.execute() mehtod. This is a asynchronous way to execute the command and you can get the resuult on Builders (Listenable or Stream) or just call .value as describled above.

If you want to get result of command just after Command.execute() you may pass a closure as bellow.

_counterCommand.execute(
    onCompleted: (value) {
        ScaffoldMessenger.of(context).showSnackBar(
            SnackBar(content: Text('Counter: $value')),
        );
    },
    onError: (error) {
        ScaffoldMessenger.of(context).showSnackBar(
            SnackBar(content: Text('Error: ${error.error}')),
        );
    },
)

copied to clipboard

Another way to execute the command is using Command.executeAsync(). It's a Future<T> so, that way you can wating for the result.

Another features

Command have all features that Stream and ValueListenable have. So you can enjoy these features too.