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。

官网地址：

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：

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。