Question

问题是当选择选项被更改时，值没有被更新。

因此，当我将本田改为丰田时，第二选择的选项变得很好，但是选择模型可以观察不到。我一定错过了什么。

JavaScript的：

function ViewModel() {
    var self = this;

    self.selectedMake = ko.observable()
    self.selectedModel = ko.observable()

    self.makes = ["Honda", "Toyota"];
    self.models = ko.computed(function () {
        if (self.selectedMake() === "Honda") return ["CRV", "Accord"];
        if (self.selectedMake() === "Toyota") return ["Rav4", "Camry"];
        return [];
    });
}
$(function () {
    ko.applyBindings(new ViewModel());
});

HTML：

<select data-bind="value: selectedMake, options: makes"></select>
<select data-bind="value: selectedModel, options: models"></select>
<p>Selected make: <b data-bind="text:selectedMake"></b></p>
<p>Selected model: <b data-bind="text:selectedModel"></b></p>

JS小提琴：http://jsfiddle.net/apuchkov/n4VyD/

Answer 1

在GitHub上找到答案。如果有人会发现这个问题，请将其重新寄到此处。

这是绑定顺序重要的情况。见http://knockoutjs.com/documentation/binding-syntax.html#notes_for_multiple_bindings_on_a_single_element

<select data-bind="options: makes, value: selectedMake"></select>
<select data-bind="options: models, value: selectedModel"></select>

jsFiddle：http://jsfiddle.net/n4VyD/4/

Answer 2

我不确定为什么它不能正常工作，但如果您设置了模型订阅，则可以手动更改所选模型。

function ViewModel() {
    var self = this;

    self.selectedMake = ko.observable()
    self.selectedModel = ko.observable()

    self.makes = ["Honda", "Toyota"];
    self.models = ko.computed(function () {
        if (self.selectedMake() === "Honda") return ["CRV", "Accord"];
        if (self.selectedMake() === "Toyota") return ["Rav4", "Camry"];
        return [];
    });

    self.models.subscribe(function(value) {
        self.selectedModel(value[0]);
    });
}

$(function () {
    ko.applyBindings(new ViewModel());
});

Fiddle

选择选项更改时，Knockoutjs不会更新值

2 个答案: