Dart编程：跨平台开发实战指南

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"Dart for Hipsters - 谷歌Dart开发技术教程，跨平台开发技术，支持PC、安卓、IOS、Pad等平台。" Dart是谷歌推出的一种面向现代Web应用的编程语言，旨在提供高效、简洁和易用的语法，以及强大的工具集。这本书《Dart for Hipsters》由Chris Strom编写，是一本针对Dart初学者和有一定经验的开发者的技术教程，旨在通过轻松易懂的方式介绍Dart语言，并深入探讨其在跨平台开发中的应用。书中可能涵盖了以下几个关键知识点： 1. **Dart语言基础**：包括Dart的基本语法、数据类型（如动态和静态类型、类与对象、接口等）、控制流（条件语句、循环）以及异常处理。 2. **函数式编程**：Dart支持函数式编程特性，如高阶函数、函数作为一等公民、闭包等。书中可能会阐述如何利用这些特性来编写更简洁、可读性强的代码。 3. **异步编程**：Dart的异步处理非常强大，通过Future和async/await关键字可以轻松处理异步操作，这在Web应用中尤其重要。书中的“isolates”部分可能详细介绍了多线程编程，这对于高性能应用来说是必不可少的。 4. **Web开发框架**：Dart的Flutter框架用于构建跨平台移动和桌面应用，而AngularDart则适用于Web开发。书里可能会讲解如何使用这些框架创建用户界面，以及它们的核心概念和最佳实践。 5. **dart2js编译器**：Dart代码可以被编译成JavaScript，使得它能在浏览器中运行。作者可能讨论了dart2js的工作原理，以及如何优化性能。 6. **开发工具**：Dart SDK包含了一整套开发工具，如Dart Editor和IntelliJ IDEA插件，这些工具可以帮助开发者提高生产力。书中会介绍如何使用这些工具进行调试、测试和性能分析。 7. **跨平台开发**：Dart不仅限于Web，还可以用于开发Android、iOS、甚至是桌面应用。书里会阐述如何利用Dart的跨平台能力来构建多平台应用程序。 8. **未来发展方向**：书中提及了对Dart未来版本特性的讨论，可能涉及即将添加的新功能或改进，帮助读者了解Dart的演进趋势。 9. **实战案例**：作者可能会通过实际项目或示例代码，展示Dart在不同场景下的应用，帮助读者将理论知识转化为实践经验。通过阅读《Dart for Hipsters》，读者不仅可以掌握Dart语言的基础知识，还能了解到如何在实际开发中充分利用Dart的优势，实现高效的跨平台应用开发。这本书对于想要提升Dart技能的开发者来说，是一份不可多得的资源。

CHAPTER

Project: Your First Dart Application

Most programming books start with a “Hello World!” sample. I say, screw that

—we’re all hipsters here. Let’s start coding!

Since Dart is written, above all else, to be familiar, we should not be too far

out of our depths diving right in. Let’s jump straight to something more fun:

an Ajax-powered website. Any true hipster has an extensive collection of

comic books (am I right? I’m not the only one, am I?), so let’s consider a

simple Dart application that manipulates the contents of that collection via

a REST-like interface.

At some point, this may prove too much of a whirlwind. Have no fear, we will

go into details in subsequent chapters.

1.1 The Back End

Sample code for this chapter can be found in the “your_first_dart_app” branch

https://github.com/eee-c/dart-comics

. As hipsters, we’re already using Node.js, so

the back end requires Node.js and npm. Instructions are contained in the

project’s README.

Being REST-like, the application should support the following:

•

GET /comics

(return a list of comic books)

•

GET /comics/42

(return a single comic book)

•

PUT /comics/42

(update a comic book entry)

•

POST /comics

(create a new comic book in the collection)

•

DELETE /comics/42

(delete a comic book)

We will not worry too much about the details of the back end beyond that.

report erratum • discuss

www.it-ebooks.info

As we will see in Chapter 10, Libraries, on page 83, there is a lot of power in

those

#import

statements. For now, we can simply think of them as a means

for pulling in functionality outside of the core Dart behavior.

All Dart applications use

main()

as the entry point for execution. Simply writing

code and expecting it to run, as we do in JavaScript, will not work here. It

might seem C-like at first, but does it honestly make sense that code lines

strewn across any number of source files and HTML will all start executing

immediately? The

main()

entry point is more than convention; it is a best

practice enforced by the language.

As for the

load_comics()

function, we take it piece by piece. We need to identify

the DOM element to which the list will attach (

#comics-list

). Next we need an

Ajax call to fill in that DOM element. To accomplish both of those things, our

first bit of Dart code might look like the following:

your_first_dart_app/_load_comics.dart

load_comics() {

var list_el = document.query('#comics-list');

ajax_populate_list(list_el);

}

Aside from the obvious omission of the

function

keyword, this example might

be JavaScript code! We will cover more differences in Chapter 3, Functional

Programming in Dart, on page 19. Still in Dart are the semicolons and curly

braces that we know and love—the language designers have certainly made

the language at least superficially familiar.

Note: Unlike in JavaScript, semicolons are not optional in Dart.

In addition to being familiar, this code is easy to read and understand at a

glance. There are no weird, legacy DOM methods. We use

document.query()

for

an element rather than

document.findByElementId()

. And we use the familiar CSS

selector of

#comics-list

, just as we have grown accustomed to in jQuery.

Having found the UL we want to populate, let’s see how to make an Ajax

request. As in JavaScript, we create a new XHR object, add a handler for

when the request loads, and then open and send the request.

your_first_dart_app/_ajax_populate_list.dart

ajax_populate_list(container) {

var req = new XMLHttpRequest();

req.on.load.add((event) {

var list = JSON.parse(req.responseText);

container.innerHTML = graphicNovelsTemplate(list);

});

6 • Chapter 1. Project: Your First Dart Application

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