8. Working with Futures, Tasks, and Isolates | DART Cookbook

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DART Cookbook

By : Ivo Balbaert

4 (2)

DART Cookbook

4 (2)

By: Ivo Balbaert

Overview of this book

If you are a Dart developer looking to sharpen your skills, and get insight and tips on how to put that knowledge into practice, then this book is for you. You should also have a basic knowledge of HTML, and how web applications with browser clients and servers work, in order to build dynamic Dart applications.

Preface

Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Free Chapter

1. Working with Dart Tools

1. Working with Dart Tools

Introduction

Configuring the Dart environment

Setting up the checked and production modes

Rapid Dart Editor troubleshooting

Hosting your own private pub mirror

Using Sublime Text 2 as an IDE

Compiling your app to JavaScript

Debugging your app in JavaScript for Chrome

Using the command-line tools

Solving problems when pub get fails

Shrinking the size of your app

Making a system call

Using snapshotting

Getting information from the operating system

2. Structuring, Testing, and Deploying an Application

2. Structuring, Testing, and Deploying an Application

Introduction

Exiting from an app

Parsing command-line arguments

Structuring an application

Using a library from within your app

Microtesting your code with assert

Unit testing a Polymer web app

Adding logging to your app

Documenting your app

Profiling and benchmarking your app

Publishing and deploying your app

Using different settings in the checked and production modes

3. Working with Data Types

3. Working with Data Types

Introduction

Concatenating strings

Using regular expressions

Strings and Unicode

Using complex numbers

Creating an enum

Flattening a list

Generating a random number within a range

Getting a random element from a list

Working with dates and times

Improving performance in numerical computations

Using SIMD for enhanced performance

4. Object Orientation

4. Object Orientation

Introduction

Testing and converting types

Comparing two objects

Using a factory constructor

Building a singleton

Using reflection

Using mixins

Using annotations

Using the call method

Using noSuchMethod

Making toJSON and fromJSON methods in your class

Creating common classes for client and server apps

5. Handling Web Applications

5. Handling Web Applications

Introduction

Responsive design

Sanitizing HTML

Using a browser's local storage

Using application cache to work offline

Preventing an onSubmit event from reloading the page

Dynamically inserting rows in an HTML table

Using CORS headers

Using keyboard events

Enabling drag-and-drop

Enabling touch events

Creating a Chrome app

Structuring a game project

Using WebGL in your app

Authorizing OAuth2 to Google services

Talking with JavaScript

Using JavaScript libraries

6. Working with Files and Streams

6. Working with Files and Streams

Introduction

Reading and processing a file line by line

Writing to a file

Searching in a file

Concatenating files

Downloading a file

Working with blobs

Transforming streams

7. Working with Web Servers

7. Working with Web Servers

Introduction

Creating a web server

Posting JSON-formatted data

Receiving data on the web server

Serving files with http_server

Using sockets

Using WebSockets

Using secure sockets and servers

Using a JSON web service

8. Working with Futures, Tasks, and Isolates

8. Working with Futures, Tasks, and Isolates

Introduction

Writing a game loop

Error handling with Futures

Scheduling tasks using Futures

Running a recurring function

Using isolates in the Dart VM

Using isolates in web apps

Using multiple cores with isolates

Using the Worker Task framework

9. Working with Databases

9. Working with Databases

Introduction

Storing data locally with IndexedDB

Using Lawndart to write offline web apps

Storing data in MySQL

Storing data in PostgreSQL

Storing data in Oracle

Storing data in MongoDB

Storing data in RethinkDB

10. Polymer Dart Recipes

10. Polymer Dart Recipes

Introduction

Data binding with polymer.dart

Binding and repeating over a list

Binding to a map

Using custom attributes and template conditionals

Binding to an input text field or a text area

Binding to a checkbox

Binding to radio buttons

Binding to a selected field

Event handling

Polymer elements with JavaScript interop

Extending DOM elements

Working with custom elements

Automatic node finding

Internationalizing a Polymer app

11. Working with Angular Dart

11. Working with Angular Dart

Introduction

Setting up an Angular app

Using a controller

Using a component

Using formatters as filters

Creating a view

Using a service

Deploying your app

Index

Index

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Error handling with Futures

This recipe shows you how to handle errors comprehensively when working with Futures. The accompanying code future_errors.dart (inside the bin map in the future_errors project) illustrates the different possibilities; however, this is not a real project, so it is not meant to be run as is.

Getting ready

When the function that returns a Future value completes successfully (calls back) signaled in the code by then, a callback function handleValue is executed that receives the value returned. If an error condition took place, the callback handleError handles it. Let's say this function is getFuture(), with Future as the result and a return value of type T, then this becomes equivalent to the following code:

Future<T> future = getFuture();
future.then(handleValue)
.catchError(handleError);

handleValue(val) {
  // processing the value
}

handleError(err) {
  // handling the error
}

The highlighted code is sometimes also written as follows, only to make the return...

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