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Foreach而不是选项绑定-复制选项标题功能?

knockout.js select

user3378165 · 技术社区 · 7 年前

我有这个选择字段:

<select data-bind="foreach: $root.feeGroups, value: $root.selectedFee">
     <optgroup data-bind="attr: {label: label}, foreach: fees">
           <option data-bind="text: description, option: $data"></option>
     </optgroup>
</select>

这个 feesGroup 属性:

 self.feeGroups([
        { label: "NEW", fees: self.fees().filter(f => f.status === "New") },
        { label: "OLD", fees: self.fees().filter(f => f.status === "Old") }
    ]);

以及 binding handler :

ko.bindingHandlers.option = {
    update: function(element, valueAccessor) {
        var value = ko.utils.unwrapObservable(valueAccessor());
        console.log(ko.toJSON(value));
        ko.selectExtensions.writeValue(element, value);
    }
};

我的问题是“optionscomption”,因为我使用foreach方法生成内部选项,它不会像我能够使用“options”绑定那样自动工作。但我需要一个“请选择…”默认选项。

有办法吗?

1 回复 | 直到 7 年前

user3297291 7 年前

您可以移动 foreach 绑定到虚拟元素,并在视图中添加表示 null 值:

<select data-bind="value: selectedFee">
  <option data-bind="text: 'Select an option', option: null"></option>
  <!-- ko foreach: feeGroups -->
  ...
  <!-- /ko -->
</select>

请记住 selectedFee 可观察的将包含 无效的 占位符处于活动状态时。

// From: https://stackoverflow.com/a/11190148/3297291
ko.bindingHandlers.option = {
  update: function(element, valueAccessor) {
    var value = ko.utils.unwrapObservable(valueAccessor());
    ko.selectExtensions.writeValue(element, value);
  }
};

const fees = [
  { type: "old", description: "test1" },
  { type: "old", description: "test2" },
  { type: "new", description: "test3" },
  { type: "new", description: "test4" }
];

const feeGroups = [
  { label: "new", fees: fees.filter(f => f.type === "new") },
  { label: "old", fees: fees.filter(f => f.type === "old") }
];

const selectedFee = ko.observable(null);
selectedFee.subscribe(console.log.bind(console, "new selection:"));

ko.applyBindings({ feeGroups, selectedFee });

<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/3.4.2/knockout-min.js"></script>

<select data-bind="value: selectedFee">
  <option data-bind="text: 'Select an option', option: null"></option>
  <!-- ko foreach: feeGroups -->
    <optgroup data-bind="attr: {label: label}, foreach: fees">
        <option data-bind="text: description, option: $data"></option>
    </optgroup>
    <!-- /ko -->
</select>