get_command

Description:

get command

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:

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++;
}
}

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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),
],
),
),
);
}
}

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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() {
cmdLongRunningTask.dispose();
}


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

A new field final GetCommand cmdLongRunningTask = GetCommand(); has been created.
During construction time we set the cmdLongRunningTask.commandFunc = _longRunningTask;. That way we tell the command which function should be executed.
OnClose() calls cmdLongRunningTask.dispose() to release any resources.

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.exec
: null,
child: controller.cmdLongRunningTask.executing
? Row(mainAxisSize: MainAxisSize.min, children: [
const Text('Executing'),
const CircularProgressIndicator(),
])
: const Text('Call computation'),
);
}),
],
),
),
);
}
}
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In that way the button is displayed as disabled and also a litte animation is displayed.

Use
controller.cmdLongRunningTask.exec
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instead of
controller.cmdLongRunningTask.commandFunc
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to assign the onPressed event handler.
The exec function calls the commandFunc function.
In the case your controller function throws an exception you have three options to handle that:

Automatically: it will be catched and the errorMessage property has a value of catchedException.toString() and the hasErrorMessage property is set to true. Here an example:

Within the _longRunningTask throw an exception:
FutureOr<void> _longRunningTask() async {
await Future.delayed(Duration(seconds: 1));
throw Exception('Ups :-(');
count.value++;
}

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since it is not catched, the Command handles it.
Lets extend the view to display the error message:
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.exec
: null,
child: controller.cmdLongRunningTask.executing
? Row(mainAxisSize: MainAxisSize.min, children: [
const Text('Executing'),
const CircularProgressIndicator(),
])
: const Text('Call computation'),
);
}),
Obx(() {
return Text(
"hasErrorMessage: ${controller.cmdLongRunningTask.hasErrorMessage}");
}),

Obx(() {
return Text(
"errorMessage: ${controller.cmdLongRunningTask.errorMessage}");
}),
],
),
),
);
}
}

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The _longRunningTask() catches the exception and sets the errorMessage via the setState(...):

FutureOr<void> _longRunningTask() async {
try {
await Future.delayed(Duration(seconds: 1));
throw Exception('Ups :-(');
count.value++;
} on Exception catch (e) {
cmdLongRunningTask.setState(
errorMessage: 'Something went wrong, try again.');
}
}
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The GetCommand has a optional errorMessageProviderFunc callback function. The function signature is defined as:

typedef ErrorMessageProvider = FutureOr<String> Function(Exception exception);
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That callback function will be called to get an error message for the given exception.
Let implement such a function within the controller:
I create a dedicated exception:
class OhNoException implements Exception {}
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that will be thrown within the _longRunningTask()function:
FutureOr<void> _longRunningTask() async {
await Future.delayed(Duration(seconds: 1));
throw OhNoException();
count.value++;
}
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I create function that have the ErrorMessageProvider signature:
FutureOr<String> _getErrorMessageFor(Exception exception) {
var errorMessage = '';

switch (exception.runtimeType) {
case OhNoException:
errorMessage = 'Oh no - what a mess, try again.';
break;
default:
errorMessage = 'Something went wrong :-(';
}

return errorMessage;
}
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and assigne that function to the errorMessageProviderFuncproperty of the GetCommand within the constructor:
HomeController() {
cmdLongRunningTask.commandFunc = _longRunningTask;
cmdLongRunningTask.errorMessageProviderFunc = _getErrorMessageFor;
}
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I Hope that GetCommand class is of any help for you.