如果没有值，则设置select的默认值

Question

I have this select :

<select data-bind="options: $root.users(), optionsText: 'name', optionsValue: 'id', value: $root.selectedUser, optionsCaption: 'Select one'"></select>

I only need the default value ('Select one') to be selected if $root.selectedUser = 0 otherwise I don't need the default value.

I tried that:

<select data-bind="options: $root.users(), optionsText: 'name', optionsValue: 'id', value: $root.selectedUser, optionsCaption: $root.selectedUser () === 0 ? 'Select one' : ''"></select>

But it's not working. (if $root.selectedUser = 0 it shows the first value of the list instead of the default value.)

Any idea on how to achieve that?

Answer 1

If this ModelView:

    var User = function(id, name) {
        this.name = name;
        this.id = id;
    };

    var viewModel = {
        users : ko.observableArray([
            new User(0,"User 1"),
            new User(2,"User 2"),
            new User(3,"User 3")
        ]),
        selectedUser : ko.observable(0)
    };


    ko.applyBindings(viewModel);

I have an User that has Id 0.

If you save in your observable any value that is an Id, it selects this option. All of this will select one option:

 selectedUser : ko.observable(0)
 selectedUser : ko.observable(2)
 selectedUser : ko.observable(3)

If you save any value, or undefined , then the default option is showed.

This fiddle shows this example.