AngularJS学习笔记之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。
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。
今天的笔记就先到这里吧，都是些个人心得，希望小伙伴们能够喜欢。
