knockout bind a key value object to dropdown

问题:

I have the following models:

var allCategories = [{
    id: 1,
    name: 'Red'},
{
    id: 5,
    name: 'Blue'}];

function model() {
    self = this;
    self.name = ko.observable("");
    self.categoryId = ko.observable(-1);
    self.categoryName = ko.computed(function() {
        if (self.categoryId() == -1) return "";
        return getCategoryNameById(self.categoryId()).name;
    });
}

function getCategoryNameById(id) {
    return _.find(allCategories, function(cat) {
        return cat.id == id;
    });
}

I want to offer a dropdown to select the category but I have no clue how to bind that. Maybe I've used the wrong approach with my models but that's most likely how I get my data from the server so I've tried to wrap my JS around that.

I tried something like this:

<select data-bind="options: categories, optionsText: 'name', value: 'id', optionsCaption: 'Categorie...'"></select>

But I don't get how to connect the dropdown value to the model categoryId.

Here is a fiddle with a working binding for the name property.

回答1:

For your list box you need to specify: options, optionsText, optionsValue, and value. value (which is the currently selected value) should point to your model.categoryId(). And optionsValue is the property name where to get values for the list:

<select data-bind="options: categories, optionsText: 'name', optionsValue: 'id', value: $root.model.categoryId(), optionsCaption: 'Categorie...'"></select>

And that's it. And the working fiddle: http://jsfiddle.net/Y7Nrc/

回答2:

According to Max Schmelevs answer, which is correct, this functionality doesn't doesn't change the JSON object when you change the item from a dropdown.

So here are my corrections for his code:

HTML Code:

<div id="container">
  <!-- Here I've added valueUpdate on keydown -->
  <input data-bind="value: model.name, valueUpdate:'afterkeydown'" />
  <!-- NOTE: Here you should call value like $root.model.categoryId -->
  <select data-bind="options: categories, optionsText: 'name', optionsValue: 'id', value: $root.model.categoryId, optionsCaption: 'Categorie...'"></select>
  <span data-bind="text: ko.toJSON($data.model)"></span>
</div>

Javascript Code:

var allCategories = [
    {id: 1, name: 'Red'},
    {id: 5, name: 'Blue'}];

function model() {
    self = this;
    self.name = ko.observable("");
    self.categoryId = ko.observable(1);
    self.categoryName = ko.computed(function() {
    //NOTE: Here we should check if categoryId() is defined or not
    if (!self.categoryId()) return "";
        return getCategoryNameById(self.categoryId()).name;
    });
}

function getCategoryNameById(id) {
    return _.find(allCategories, function(cat) {
        return cat.id == id;
    });
}

var viewModel = {};
viewModel.model = new model();
viewModel.categories = allCategories;
ko.applyBindings(viewModel, document.getElementById('container'));

!!!IMPORTANT!!!

If this approach answers your question, please select Max Shmelev's answer as correct, not mine, because I've just put some remarks in his code.