get_command 2.0.0-nullsafety.1

Command class to be used within GetControllers. Encapsulate a async function call to simplify UI updates.

get_command

This library helps providing feedback to the user while executing a controller function. It is intended to be used with the Get library.

Let's create an example to showcase the usage:

1. Create a controller with an async function 'longRunningTask':

import 'package:get/get.dart';

class HomeController extends GetxController {
  final count = 0.obs;

  @override
  void onInit() {
    super.onInit();
  }

  @override
  void onReady() {
    super.onReady();
  }

  @override
  void onClose() {}

  Future<void> longRunningTask() async {
    await Future.delayed(Duration(seconds: 1));
    count.value++;
  }
}

2. Create a simple view

import 'package:flutter/material.dart';
import 'package:get/get.dart';

import '../controllers/home_controller.dart';

class HomeView extends GetView<HomeController> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('HomeView'),
        centerTitle: true,
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Obx(() {
              return Text("Current value: ${controller.count}");
            }),
            ElevatedButton(
                child: const Text("Start long running task"),
                onPressed: controller.longRunningTask),
          ],
        ),
      ),
    );
  }
}

The problem with this code is that user can tap the button again while the longRunningTask function is currently beening executed.

Let's extend the controller to use a GetCommand:

import 'dart:async';

import 'package:get/get.dart';
import 'package:get_command/get_command.dart';

class HomeController extends GetxController {
  final count = 0.obs;
  final GetCommand cmdLongRunningTask = GetCommand();

  HomeController() {
    cmdLongRunningTask.commandFunc = _longRunningTask;
  }

  @override
  void onInit() {
    super.onInit();
  }

  @override
  void onReady() {
    super.onReady();
  }

  @override
  void onClose() {}

  FutureOr<void> _longRunningTask() async {
    await Future.delayed(Duration(seconds: 1));
    count.value++;
  }
}

What changed:

1. A new field final GetCommand cmdLongRunningTask = GetCommand(); has been created.
2. During construction time we set the cmdLongRunningTask.commandFunc = _longRunningTask;. That way we tell the command which function should be executed.

Next we update the HomeView to use the Command:

import 'package:flutter/material.dart';
import 'package:get/get.dart';
import 'package:get_command_example/app/modules/home/controllers/home_controller.dart';

class HomeView extends GetView<HomeController> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('HomeView'),
        centerTitle: true,
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Obx(() {
              return Text("Current value: ${controller.count}");
            }),
            Obx(() {
              return ElevatedButton(
                onPressed: controller.cmdLongRunningTask.canBeExecuted
                    ? controller.cmdLongRunningTask
                    : null,
                child: controller.cmdLongRunningTask.executing
                    ? Row(mainAxisSize: MainAxisSize.min, children: [
                        const Text('Executing'),
                        const CircularProgressIndicator(),
                      ])
                    : const Text('Call computation'),
              );
            }),
          ],
        ),
      ),
    );
  }
}

In this way the button is displayed as disabled during execution and also displays a little animation. A GetCommand is a callable class, you can simply use:

controller.cmdLongRunningTask

instead of

controller.cmdLongRunningTask.commandFunc

In the case your controller function throws an exception, it will be catched and the errorMessage property has a value of catchedException.toString().

If you catch any exception within your controller function, you can provide the error message via

code

Rember to call the dispose() function to release any associated resource: That are subscriptions to the state property and the commandFunc and errorMessageProviderFunc will be set to null.

I Hope that Command class is of any help for you.