简单应用举例（1）

## 1   Hello world 这个例子里，2个输入框都被绑定到data model上的observable变量上。“full name”显示的是一个dependent observable，它的值是前面2个输入框的值合并一起的结果。    无论哪个输入框更新，都会看到“full name” 显示结果都会自动更新。查看HTML源代码可以看到我们不需要声明onchange事件。Knockout知道什么时候该更新UI。 **代码: View** ~~~ <p>First name: <input data-bind="value: firstName"/></p> <p>Last name: <input data-bind="value: lastName"/></p> <h2>Hello, <span data-bind="text: fullName"> </span>!</h2> ~~~ **代码**: View model ~~~ // 这里是声明的view model var viewModel = { firstName: ko.observable("Planet"), lastName: ko.observable("Earth") }; viewModel.fullName = ko.dependentObservable(function () { // Knockout tracks dependencies automatically. //It knows that fullName depends on firstName and lastName, //because these get called when evaluating fullName. return viewModel.firstName() + " " + viewModel.lastName(); }); ko.applyBindings(viewModel); // This makes Knockout get to work ~~~ ## 2   Click counter 这个例子展示的创建一个view model并且绑定各种绑定到HTML元素标记上，以便展示和修改view model的状态。 Knockout根据依赖项。在内部，hasClickedTooManyTimes在numberOfClicks上有个订阅，以便当numberOfClicks改变的时候，强制hasClickedTooManyTimes重新执行。相似的，UI界面上多个地方引用hasClickedTooManyTimes，所以当hasClickedTooManyTimes 改变的时候，也讲导致UI界面更新。 不需要手工声明或者订阅这些subscription订阅，他们由KO框架自己创建和销毁。参考如下代码实现：   **代码**: View ~~~ <div>You've clicked <span data-bind="text: numberOfClicks">&nbsp;</span> times</div> <button data-bind="click: registerClick, enable: !hasClickedTooManyTimes()">Click me</button> <div data-bind="visible: hasClickedTooManyTimes"> That's too many clicks! Please stop before you wear out your fingers. <button data-bind="click: function() { numberOfClicks(0) }">Reset clicks</button> </div> ~~~ **代码**: View model ~~~ var clickCounterViewModel = function () { this.numberOfClicks = ko.observable(0); this.registerClick = function () { this.numberOfClicks(this.numberOfClicks() + 1); } this.hasClickedTooManyTimes = ko.dependentObservable(function () { return this.numberOfClicks() >= 3; }, this); }; ko.applyBindings(new clickCounterViewModel()); ~~~ ## 3   Simple list 这个例子展示的是绑定到数组上。 注意到，只有当你在输入框里输入一些值的时候，Add按钮才可用。参考下面的HTML代码是如何使用enable 绑定。   **代码**: View ~~~ <form data-bind="submit: addItem"> New item: <input data-bind='value: itemToAdd, valueUpdate: "afterkeydown"' /> <button type="submit" data-bind="enable: itemToAdd().length > 0">Add</button> <p>Your items:</p> <select multiple="multiple" width="50" data-bind="options: items"> </select> </form> ~~~ **代码**: View model ~~~ var viewModel = {}; viewModel.items = ko.observableArray(["Alpha", "Beta", "Gamma"]); viewModel.itemToAdd = ko.observable(""); viewModel.addItem = function () { if (viewModel.itemToAdd() != "") { viewModel.items.push(viewModel.itemToAdd()); // Adds the item. Writing to the "items" observableArray causes any associated UI to update. viewModel.itemToAdd(""); // Clears the text box, because it's bound to the "itemToAdd" observable } } ko.applyBindings(viewModel); ~~~ ## 4   Better list 这个例子是在上个例子的基础上添加remove item功能（multi-selection）和排序功能。 “remove”和“sort”按钮在不能用的时候会变成disabled状态（例如，没有足够的item来排序）。 参考HTML代码是如何实现这些功能的，另外这个例子也展示了如何使用匿名函数来实现排序。   **代码**: View ~~~ <form data-bind="submit:addItem"> Add item: <input type="text" data-bind='value:itemToAdd, valueUpdate: "afterkeydown"' /> <button type="submit" data-bind="enable: itemToAdd().length > 0">Add</button> </form> <p>Your values:</p> <select multiple="multiple" height="5" data-bind="options:allItems, selectedOptions:selectedItems"> </select> <div> <button data-bind="click: removeSelected, enable: selectedItems().length > 0">Remove</button> <button data-bind="click: function() { allItems.sort() }, enable: allItems().length > 1">Sort</button> </div> ~~~ **代码**: View model ~~~ // In this example, betterListModel is a class, and the view model is an instance of it. // See simpleList.html for an example of how to construct a view model without defining a class for it. Either technique works fine. var betterListModel = function () { this.itemToAdd = new ko.observable(""); this.allItems = new ko.observableArray(["Fries", "Eggs Benedict", "Ham", "Cheese"]); // Initial items this.selectedItems = new ko.observableArray(["Ham"]); // Initial selection this.addItem = function () { if ((this.itemToAdd() != "") && (this.allItems.indexOf(this.itemToAdd()) < 0)) // Prevent blanks and duplicates this.allItems.push(this.itemToAdd()); this.itemToAdd(""); // Clear the text box } this.removeSelected = function () { this.allItems.removeAll(this.selectedItems()); this.selectedItems([]); // Clear selection } }; ko.applyBindings(new betterListModel()); ~~~