AngularJS的学习--TodoMVC的分析

最近一段时间一直在看AngularJS，趁着一点时间总结一下。

官网地址：http://angularjs.org/

先推荐几个教程

1. AngularJS入门教程 比较基础，是官方Tutorial的翻译。

2. 七步从AngularJS菜鸟到专家 也比较基础，制作了一个在线音乐播放网站。

3. AngularJS开发指南 这个教程比较全面，但我感觉翻译的有些晦涩难懂。

看过这些教程后，觉得AngularJS也懂一点了，就想用它干点事，就分析一下AngularJS写的todomvc吧。

Todomvc官网地址：http://todomvc.com/

项目的目录如下：

bower_components里放了两个文件夹，其中angular文件夹是用来一如angular.js文件的，todomvc-common文件夹里的放入了所有todo项目统一的css\js(只是用来生成左侧内容的，与项目无关)和图片。

js文件夹是大头，里面放了相应的controller(控制器)\directive(指令)\service(服务)和app.js。

test文件夹里放的是测试用的代码，不分析。

index.html是项目的view页面。

先来看一下app.js

/*global angular */
/*jshint unused:false */
'use strict';

/**
 * The main TodoMVC app module
 *
 * @type {angular.Module}
 */
var todomvc = angular.module('todomvc', []);

就是定义了一个模块todomvc

再看一下services下的todoStorage.js

/*global todomvc */
'use strict';

/**
 * Services that persists and retrieves TODOs from localStorage
 */
todomvc.factory('todoStorage', function () {
    // todos JSON字符串存储的唯一标识
    var STORAGE_ID = 'todos-angularjs';

    return {
        // 从localStorage中取出todos，并解析成JSON对象
        get: function () {
            return JSON.parse(localStorage.getItem(STORAGE_ID) || '[]');
        },

        // 将todos对象转化成JSON字符串，并存入localStorage
        put: function (todos) {
            localStorage.setItem(STORAGE_ID, JSON.stringify(todos));
        }
    };
});

使用factory方法创建了todoStorage的service方法，这个service方法的本质就是返回了两个方法get和put，两者都是用了JSON2和HTML5的特性。get将todos的内容从localStorage中取出，并解析成JSON，put将todos转化成JSON字符串，并存储到localStorage中。

再看一下directives下面的两个指令文件。

todoFocus.js

/*global todomvc */
'use strict';

/**
 * Directive that places focus on the element it is applied to when the expression it binds to evaluates to true
 */
todomvc.directive('todoFocus', function todoFocus($timeout) {
    return function (scope, elem, attrs) {
        // 为todoFocus属性的值添加监听
        scope.$watch(attrs.todoFocus, function (newVal) {
            if (newVal) {
                $timeout(function () {
                    elem[0].focus();
                }, 0, false);
            }
        });
    };
});

返回function的参数中，elem就是包含该指令的元素的数组，attrs是元素的所有属性、属性名等组成的对象。

其中用到了两个AngularJS的方法

$watch(watchExpression, listener, objectEquality) 注册一个侦听器回调，每当watchExpression变化时，监听回调将被执行。

$timeout(fn[, delay][, invokeApply]) 当timeout的值达到时，执行fn函数。

todoFocus.js创建了todoFocus指令。当一个元素拥有todoFocus属性时，该指令会为该元素的todoFocus属性的值添加监听，如果todoFocus属性的值改变成true，就会执行$timeout(function () {elem[0].focus();}, 0, false);其中的延迟时间为0秒，所以会立即执行elem[0].focus()。

todoEscape.js

/*global todomvc */
'use strict';

/**
 * Directive that executes an expression when the element it is applied to gets
 * an `escape` keydown event.
 */
todomvc.directive('todoEscape', function () {
    var ESCAPE_KEY = 27;
    return function (scope, elem, attrs) {
        elem.bind('keydown', function (event) {
            if (event.keyCode === ESCAPE_KEY) {
                scope.$apply(attrs.todoEscape);
            }
        });
    };
});

todoEscape.js创建了todoEscape指令。当按下Escape键时，执行attrs.todoEscape的表达式。

看一下大头，controllers文件夹中的todoCtrl.js，这个文件略长，我就直接写注释了。

/*global todomvc, angular */
'use strict';

/**
 * The main controller for the app. The controller:
 * - retrieves and persists the model via the todoStorage service
 * - exposes the model to the template and provides event handlers
 */
todomvc.controller('TodoCtrl', function TodoCtrl($scope, $location, todoStorage, filterFilter) {
    // 从localStorage中获取todos
    var todos = $scope.todos = todoStorage.get();

    // 记录新的todo
    $scope.newTodo = '';
    // 记录编辑过的todo
    $scope.editedTodo = null;

    // 当todos的值改变时执行其中的方法
    $scope.$watch('todos', function (newValue, oldValue) {
        // 获取未完成的todos的数目
        $scope.remainingCount = filterFilter(todos, { completed: false }).length;
        // 获取已完成的todos的数目
        $scope.completedCount = todos.length - $scope.remainingCount;
        // 当且仅当$scope.remainingCount为0时，$scope.allChecked为true
        $scope.allChecked = !$scope.remainingCount;
        // 当todos的新值和旧值不相等时，向localStorage中存入todos
        if (newValue !== oldValue) { // This prevents unneeded calls to the local storage
            todoStorage.put(todos);
        }
    }, true);

    if ($location.path() === '') {
        // 如果$location.path()为空，就设置为/
        $location.path('/');
    }

    $scope.location = $location;

    // 当location.path()的值改变时执行其中的方法
    $scope.$watch('location.path()', function (path) {
        // 获取状态的过滤器
        // 如果path为'/active'，过滤器为{ completed: false }
        // 如果path为'/completed'，过滤器为{ completed: true }
        // 否则，过滤器为null
        $scope.statusFilter = (path === '/active') ?
            { completed: false } : (path === '/completed') ?
            { completed: true } : null;
    });

    // 添加一个新的todo
    $scope.addTodo = function () {
        var newTodo = $scope.newTodo.trim();
        if (!newTodo.length) {
            return;
        }

        // 向todos里添加一个todo，completed属性默认为false
        todos.push({
            title: newTodo,
            completed: false
        });

        // 置空
        $scope.newTodo = '';
    };

    // 编辑一个todo
    $scope.editTodo = function (todo) {
        $scope.editedTodo = todo;
        // Clone the original todo to restore it on demand.
        // 保存编辑前的todo，为恢复编辑前做准备
        $scope.originalTodo = angular.extend({}, todo);
    };

    // 编辑todo完成
    $scope.doneEditing = function (todo) {
        // 置空
        $scope.editedTodo = null;
        todo.title = todo.title.trim();

        if (!todo.title) {
            // 如果todo的title为空，则移除该todo
            $scope.removeTodo(todo);
        }
    };

    // 恢复编辑前的todo
    $scope.revertEditing = function (todo) {
        todos[todos.indexOf(todo)] = $scope.originalTodo;
        $scope.doneEditing($scope.originalTodo);
    };

    // 移除todo
    $scope.removeTodo = function (todo) {
        todos.splice(todos.indexOf(todo), 1);
    };

    // 清除已完成的todos
    $scope.clearCompletedTodos = function () {
        $scope.todos = todos = todos.filter(function (val) {
            return !val.completed;
        });
    };

    // 标记所有的todo的状态（true或false）
    $scope.markAll = function (completed) {
        todos.forEach(function (todo) {
            todo.completed = completed;
        });
    };
}); 

最后看一下index.html，这个文件我们一段一段的分析。

<!doctype html>
<html lang="en" ng-app="todomvc" data-framework="angularjs">
    <head>
        <meta charset="utf-8">
        <meta http-equiv="X-UA-Compatible" content="IE=edge">
        <title>AngularJS • TodoMVC</title>
        <link rel="stylesheet" href="bower_components/todomvc-common/base.css">
        <style>[ng-cloak] { display: none; }</style>
    </head>
    <body>
        <section id="todoapp" ng-controller="TodoCtrl">
            <header id="header">
                <h1>todos</h1>
                <form id="todo-form" ng-submit="addTodo()">
                    <input id="new-todo" placeholder="What needs to be done?" ng-model="newTodo" autofocus>
                </form>
            </header>
            <section id="main" ng-show="todos.length" ng-cloak>
                <input id="toggle-all" type="checkbox" ng-model="allChecked" ng-click="markAll(allChecked)">
                <label for="toggle-all">Mark all as complete</label>
                <ul id="todo-list">
                    <li ng-repeat="todo in todos | filter:statusFilter track by $index" ng-class="{completed: todo.completed, editing: todo == editedTodo}">
                        <div class="view">
                            <input class="toggle" type="checkbox" ng-model="todo.completed">
                            <label ng-dblclick="editTodo(todo)">{{todo.title}}</label>
                            <button class="destroy" ng-click="removeTodo(todo)"></button>
                        </div>
                        <form ng-submit="doneEditing(todo)">
                            <input class="edit" ng-trim="false" ng-model="todo.title" todo-escape="revertEditing(todo)" ng-blur="doneEditing(todo)" todo-focus="todo == editedTodo">
                        </form>
                    </li>
                </ul>
            </section>
            <footer id="footer" ng-show="todos.length" ng-cloak>
                <span id="todo-count"><strong>{{remainingCount}}</strong>
                    <ng-pluralize count="remainingCount" when="{ one: 'item left', other: 'items left' }"></ng-pluralize>
                </span>
                <ul id="filters">
                    <li>
                        <a ng-class="{selected: location.path() == '/'} " href="#/">All</a>
                    </li>
                    <li>
                        <a ng-class="{selected: location.path() == '/active'}" href="#/active">Active</a>
                    </li>
                    <li>
                        <a ng-class="{selected: location.path() == '/completed'}" href="#/completed">Completed</a>
                    </li>
                </ul>
                <button id="clear-completed" ng-click="clearCompletedTodos()" ng-show="completedCount">Clear completed ({{completedCount}})</button>
            </footer>
        </section>
        <footer id="info">
            <p>Double-click to edit a todo</p>
            <p>Credits:
                <a href="http://twitter.com/cburgdorf">Christoph Burgdorf</a>,
                <a href="http://ericbidelman.com">Eric Bidelman</a>,
                <a href="http://jacobmumm.com">Jacob Mumm</a> and
                <a href="http://igorminar.com">Igor Minar</a>
            </p>
            <p>Part of <a href="http://todomvc.com">TodoMVC</a></p>
        </footer>
        <script src="bower_components/todomvc-common/base.js"></script>
        <script src="bower_components/angular/angular.js"></script>
        <script src="js/app.js"></script>
        <script src="js/controllers/todoCtrl.js"></script>
        <script src="js/services/todoStorage.js"></script>
        <script src="js/directives/todoFocus.js"></script>
        <script src="js/directives/todoEscape.js"></script>
    </body>
</html>

首先是在最下面，引入相应的JS，这个就不多说了。

<script src="bower_components/todomvc-common/base.js"></script>
<script src="bower_components/angular/angular.js"></script>
<script src="js/app.js"></script>
<script src="js/controllers/todoCtrl.js"></script>
<script src="js/services/todoStorage.js"></script>
<script src="js/directives/todoFocus.js"></script>
<script src="js/directives/todoEscape.js"></script>

定义style[ng-cloak]，含有ng-cloak属性则不可见。

<style>[ng-cloak] { display: none; }</style>

来看添加todo的html，绑定的model为newTodo，submit的方法是todoCtrl.js中的addTodo()，会添加一条todo，点击Enter，默认触发提交事件，就触发了addTodo()方法，添加了一条todo到todos中。

<form id="todo-form" ng-submit="addTodo()">
    <input id="new-todo" placeholder="What needs to be done?" ng-model="newTodo" autofocus>
</form>

再看展示todos的html

<section id="main" ng-show="todos.length" ng-cloak>
    <input id="toggle-all" type="checkbox" ng-model="allChecked" ng-click="markAll(allChecked)">
    <label for="toggle-all">Mark all as complete</label>
    <ul id="todo-list">
        <li ng-repeat="todo in todos | filter:statusFilter track by $index" ng-class="{completed: todo.completed, editing: todo == editedTodo}">
            <div class="view">
                <input class="toggle" type="checkbox" ng-model="todo.completed">
                <label ng-dblclick="editTodo(todo)">{{todo.title}}</label>
                <button class="destroy" ng-click="removeTodo(todo)"></button>
            </div>
            <form ng-submit="doneEditing(todo)">
                <input class="edit" ng-trim="false" ng-model="todo.title" todo-escape="revertEditing(todo)" ng-blur="doneEditing(todo)" todo-focus="todo == editedTodo">
            </form>
        </li>
    </ul>
</section>

section使用ngShow方法根据todos的长度判断是否显示，加上ng-cloak属性是为了在刚开始时不要显示出AngularJS未处理的页面。可以去掉刷新试一试。

其中id为toggle-all的checkbox绑定到allChecked model上，点击触发markAll(allChecked)，将allChecked的值传入，标记所有的todos。

使用ngRepeat循环产生li标签，todo in todos | filter:statusFilter track by $index，循环todos，用statusFilter过滤，用$index追踪。ngClass绑定了两个class，{completed: todo.completed, editing: todo == editedTodo}，如果todo.completed为true，添加completed class，如果todo==editedTodo，则添加editing class。class为toggle的checkbox绑定到todo.completed。todo标题展示的label绑定了双击事件，双击触发editTodo(todo)，editTodo会将todo赋给editedTodo，然后会触发下面form中的todoFocus指令，这时候form中的input可见。按Esc就触发revertEditing(todo)，恢复到编辑前，按Enter或者失去焦点就触发doneEditing(todo) ，保存编辑后的todo。class为destroy的button绑定了click事件，点击触发removeTodo(todo)，删除掉该条todo。

最后看todos的统计信息展示的html

<footer id="footer" ng-show="todos.length" ng-cloak>
    <span id="todo-count"><strong>{{remainingCount}}</strong>
        <ng-pluralize count="remainingCount" when="{ one: 'item left', other: 'items left' }"></ng-pluralize>
    </span>
    <ul id="filters">
        <li>
            <a ng-class="{selected: location.path() == '/'} " href="#/">All</a>
        </li>
        <li>
            <a ng-class="{selected: location.path() == '/active'}" href="#/active">Active</a>
        </li>
        <li>
            <a ng-class="{selected: location.path() == '/completed'}" href="#/completed">Completed</a>
        </li>
    </ul>
    <button id="clear-completed" ng-click="clearCompletedTodos()" ng-show="completedCount">Clear completed ({{completedCount}})</button>
</footer>

ng-pluralize标签实现了当remainingCount个数为1时，显示 item left，否则显示 items left。

id为filters的ul标签中根据location.path()的内容不同，标记不同的a标签被选中。

id为clear-completed的button添加了点击事件，触发clearCompletedTodos()，清除掉所有已完成的todo。

分析到此结束，如有错误，或者有不明白的地方，请留言~~