knockoutjs foreach array绑定表格下拉框绑定

转载http://desert3.iteye.com/blog/1480471

knockoutjs foreach array绑定表格下拉框绑定

博客分类：

Javascript

动态表格使用observable arrays and the foreach
ko.observableArray：观察者模式，根据array动态更新表格

ko中的流程控制标签：foreach, if, ifnot, and with
在foreach的数据源发生变化时，ko并不会重新生成整个table，更高效地，ko会找到viewmodel中变化的部分，然后更新数据变化对应的最小DOM集合。

data-bind="foreach: seats"：foreach表格循环
meal().price： meal属性是一个被观察对象，在尝试取得子属性之前要使用meal()函数，即注意是meal().price, 不是 meal.price

data-bind="click: addSeat, enable: seats().length < 5"：表示按钮绑定到click事件addSeat，并且按钮只在表格数据小于5时可用，删错或者增加表格数据，由于ko的自动依赖追踪机制，按钮的可用状态会自动变化。

data-bind="visible: totalSurcharge() > 0":用来控制控件是否显示，对应css的display 属性

$root.前缀代表Knockout去viewmodel的顶层查询相应属性，而不是绑定表格seats数组中的实例变量SeatReservation中查询。

必须是引用方法的形式（带括号）引用observable变量，这与ko的自动依赖追踪相对象（如果是属性的话，就仅仅引用变量的值，做不到其他效果）

// 下拉框绑定到$root.availableMeals数组，下拉框显示的文字内容由optionsText: 'mealName'决定，下拉框的值绑定到seats数组中对象SeatReservation的meal属性！
<select data-bind="options: $root.availableMeals, value: meal, optionsText: 'mealName'"></select>

viewmodel（控制器）

// Class to represent a row in the seat reservations grid
function SeatReservation(name, initialMeal) {
var self = this;
self.name = name;
self.meal = ko.observable(initialMeal);
self.formattedPrice = ko.computed(function() {
var price = self.meal().price;
return price ? "$" + price.toFixed(2) : "None";
});
}
// Overall viewmodel for this screen, along with initial state
function ReservationsViewModel() {
var self = this;
// Non-editable catalog data - would come from the server
self.availableMeals = [
{ mealName: "Standard (sandwich)", price: 0 },
{ mealName: "Premium (lobster)", price: 34.95 },
{ mealName: "Ultimate (whole zebra)", price: 290 }
];
// Editable data
self.seats = ko.observableArray([
new SeatReservation("Steve", self.availableMeals[0]),
new SeatReservation("Bert", self.availableMeals[0])
]);
// Operations
self.addSeat = function() {
self.seats.push(new SeatReservation("", self.availableMeals[0]));
}
self.removeSeat = function(seat) { self.seats.remove(seat) }
self.totalSurcharge = ko.computed(function() {
var total = 0;
for (var i = 0; i < self.seats().length; i++)
total += self.seats()[i].meal().price;
return total;
});
}
ko.applyBindings(new ReservationsViewModel());

view视图

<h2>Your seat reservations</h2>
<table>
<thead><tr>
<th>Passenger name</th><th>Meal</th><th>Surcharge</th><th></th>
</tr></thead>
<tbody data-bind="foreach: seats">
<tr>
<td><input data-bind="value: name" /></td>
<td><select data-bind="options: $root.availableMeals, value: meal, optionsText: 'mealName'"></select></td>
<td data-bind="text: meal().price"></td>
<td data-bind="text: formattedPrice"></td>
<td><a href="#" data-bind="click: $root.removeSeat">Remove</a></td>
</tr>
</tbody>
</table>
<h3 data-bind="visible: totalSurcharge() > 0">
Total surcharge: $<span data-bind="text: totalSurcharge().toFixed(2)"></span>
</h3>
<h2>Your seat reservations (<span data-bind="text: seats().length"></span>)</h2>
<button data-bind="click: addSeat, enable: seats().length < 5">Reserve another seat</button>