AngularJS的學習--TodoMVC的分析

最近一段時間一直在看AngularJS，趁着一點時間總結一下。

官網地址：http://angularjs.org/

先推薦幾個教程

1. AngularJS入門教程 比較基礎，是官方Tutorial的翻譯。

2. 七步從AngularJS菜鳥到專家 也比較基礎，制作了一個在線音樂播放網站。

3. AngularJS開發指南 這個教程比較全面，但我感覺翻譯的有些晦澀難懂。

看過這些教程后，覺得AngularJS也懂一點了，就想用它干點事，就分析一下AngularJS寫的todomvc吧。

Todomvc官網地址：http://todomvc.com/

項目的目錄如下：

bower_components里放了兩個文件夾，其中angular文件夾是用來一如angular.js文件的，todomvc-common文件夾里的放入了所有todo項目統一的css\js(只是用來生成左側內容的，與項目無關)和圖片。

js文件夾是大頭，里面放了相應的controller(控制器)\directive(指令)\service(服務)和app.js。

test文件夾里放的是測試用的代碼，不分析。

index.html是項目的view頁面。

 

先來看一下app.js

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

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

就是定義了一個模塊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字符串存儲的唯一標識
    var STORAGE_ID = 'todos-angularjs';

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

        // 將todos對象轉化成JSON字符串，並存入localStorage
        put: function (todos) {
            localStorage.setItem(STORAGE_ID, JSON.stringify(todos));
        }
    };
});

使用factory方法創建了todoStorage的service方法，這個service方法的本質就是返回了兩個方法get和put，兩者都是用了JSON2和HTML5的特性。get將todos的內容從localStorage中取出，並解析成JSON，put將todos轉化成JSON字符串，並存儲到localStorage中。

 

再看一下directives下面的兩個指令文件。

 

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($timeout) {
    return function (scope, elem, attrs) {
        // 為todoFocus屬性的值添加監聽
        scope.$watch(attrs.todoFocus, function (newVal) {
            if (newVal) {
                $timeout(function () {
                    elem[0].focus();
                }, 0, false);
            }
        });
    };
});

返回function的參數中，elem就是包含該指令的元素的數組，attrs是元素的所有屬性、屬性名等組成的對象。

其中用到了兩個AngularJS的方法

$watch(watchExpression, listener, objectEquality) 注冊一個偵聽器回調，每當watchExpression變化時，監聽回調將被執行。

$timeout(fn[, delay][, invokeApply]) 當timeout的值達到時，執行fn函數。

todoFocus.js創建了todoFocus指令。當一個元素擁有todoFocus屬性時，該指令會為該元素的todoFocus屬性的值添加監聽，如果todoFocus屬性的值改變成true，就會執行$timeout(function () {elem[0].focus();}, 0, false);其中的延遲時間為0秒，所以會立即執行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創建了todoEscape指令。當按下Escape鍵時，執行attrs.todoEscape的表達式。

 

看一下大頭，controllers文件夾中的todoCtrl.js，這個文件略長，我就直接寫注釋了。

/*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) {
    // 從localStorage中獲取todos
    var todos = $scope.todos = todoStorage.get();

    // 記錄新的todo
    $scope.newTodo = '';
    // 記錄編輯過的todo
    $scope.editedTodo = null;

    // 當todos的值改變時執行其中的方法
    $scope.$watch('todos', function (newValue, oldValue) {
        // 獲取未完成的todos的數目
        $scope.remainingCount = filterFilter(todos, { completed: false }).length;
        // 獲取已完成的todos的數目
        $scope.completedCount = todos.length - $scope.remainingCount;
        // 當且僅當$scope.remainingCount為0時，$scope.allChecked為true
        $scope.allChecked = !$scope.remainingCount;
        // 當todos的新值和舊值不相等時，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()為空，就設置為/
        $location.path('/');
    }

    $scope.location = $location;

    // 當location.path()的值改變時執行其中的方法
    $scope.$watch('location.path()', function (path) {
        // 獲取狀態的過濾器
        // 如果path為'/active'，過濾器為{ completed: false }
        // 如果path為'/completed'，過濾器為{ completed: true }
        // 否則，過濾器為null
        $scope.statusFilter = (path === '/active') ?
            { completed: false } : (path === '/completed') ?
            { completed: true } : null;
    });

    // 添加一個新的todo
    $scope.addTodo = function () {
        var newTodo = $scope.newTodo.trim();
        if (!newTodo.length) {
            return;
        }

        // 向todos里添加一個todo，completed屬性默認為false
        todos.push({
            title: newTodo,
            completed: false
        });

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

    // 編輯一個todo
    $scope.editTodo = function (todo) {
        $scope.editedTodo = todo;
        // Clone the original todo to restore it on demand.
        // 保存編輯前的todo，為恢復編輯前做准備
        $scope.originalTodo = angular.extend({}, todo);
    };

    // 編輯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為空，則移除該todo
            $scope.removeTodo(todo);
        }
    };

    // 恢復編輯前的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;
        });
    };

    // 標記所有的todo的狀態（true或false）
    $scope.markAll = function (completed) {
        todos.forEach(function (todo) {
            todo.completed = completed;
        });
    };
}); 

 最后看一下index.html，這個文件我們一段一段的分析。

<!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，引入相應的JS，這個就不多說了。

<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>

定義style[ng-cloak]，含有ng-cloak屬性則不可見。

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

來看添加todo的html，綁定的model為newTodo，submit的方法是todoCtrl.js中的addTodo()，會添加一條todo，點擊Enter，默認觸發提交事件，就觸發了addTodo()方法，添加了一條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方法根據todos的長度判斷是否顯示，加上ng-cloak屬性是為了在剛開始時不要顯示出AngularJS未處理的頁面。可以去掉刷新試一試。

其中id為toggle-all的checkbox綁定到allChecked model上，點擊觸發markAll(allChecked)，將allChecked的值傳入，標記所有的todos。

使用ngRepeat循環產生li標簽，todo in todos | filter:statusFilter track by $index，循環todos，用statusFilter過濾，用$index追蹤。ngClass綁定了兩個class，{completed: todo.completed, editing: todo == editedTodo}，如果todo.completed為true，添加completed class，如果todo==editedTodo，則添加editing class。class為toggle的checkbox綁定到todo.completed。todo標題展示的label綁定了雙擊事件，雙擊觸發editTodo(todo)，editTodo會將todo賦給editedTodo，然后會觸發下面form中的todoFocus指令，這時候form中的input可見。按Esc就觸發revertEditing(todo)，恢復到編輯前，按Enter或者失去焦點就觸發doneEditing(todo) ，保存編輯后的todo。class為destroy的button綁定了click事件，點擊觸發removeTodo(todo)，刪除掉該條todo。

最后看todos的統計信息展示的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標簽實現了當remainingCount個數為1時，顯示 item left，否則顯示 items left。

id為filters的ul標簽中根據location.path()的內容不同，標記不同的a標簽被選中。

id為clear-completed的button添加了點擊事件，觸發clearCompletedTodos()，清除掉所有已完成的todo。

 

分析到此結束，如有錯誤，或者有不明白的地方，請留言~~