Knockout value not being set in function

问题

I am having a problem when trying to get self.material (an observable) to load a value from within a function. When trying to load the observable in the select with a value, it shows as undefined. data.materialNumber has a string value and self.materials loads correctly. Any help would be appreciated!

I'll try to include only the code needed...

My html:

<select class="materialSelect" data-placeholder="Choose Material..." 
                                data-bind="options: materials,
                            value: material,
                            optionsText: function (item) { return item.description }, 
                            optionsValue: function (item) { return item.materialNumber },
                            chosen: materials,
                            chosenOptions: { width: '250px', search_contains: true }"></select>

My js:

function Mrs() {

var self = this;


self.materials = ko.observableArray();
self.material = ko.observable("");


bom.hubs.mrs.server()
    .getMaterialsForAuthorizedPlants(lastSection)
    .done(function (data) {
        data.materials.unshift({});
        self.material(data.materialNumber);
        self.materials(data.materials);
    });
 };
(function (bom) {
    "use strict";

    bom.hubs.done(function() {
        ko.applyBindings(new Mrs());
    });

})(bom);

回答1:

TL;DR Assign self.materials before self.material

---

The options binding will attempt to synchronise the selected option with the value, but when you assign self.material there are NO options, so it resets the material value back to undefined.

When you then set self.materials, the options then rebuilds, but self.material is now undefined.

If you swap the assignments, then the select options will be available when the material observable is set.

来源：https://stackoverflow.com/questions/21682961/knockout-value-not-being-set-in-function