Using a kendo observable property in multiple viewModels

Question

In a Kendo app using the Kendo MVVM framework: I have a "global" viewModel which is information that is common to all parts of the app - e.g. the UserState, which has a property isLoggedIn.

Many different Views and ViewModels access the userState object (from what I can see, 1 View is bound to 1 ViewModel in Kendo).

For example, my home page might show the Login button if they are not authenticated. Then all the other screens behave differently once you are logged in, so each ViewModel needs to reference the UserState object. However, if any of them change it then all other Views should update as I used a Kendo Observable object. This does not seem to work.

I set up a simple example here to illustrate the problem: http://jsfiddle.net/rodneyjoyce/uz7ph/11

var app = new kendo.mobile.Application();   

userState = (function ()
{
    var userStateViewModel = kendo.observable({
                                                  isLoggedIn: false
                                              });    
    function loginUser()
    {
        userStateViewModel.set("isLoggedIn", true);
        alert('Logged in');
    };

    return {            
        userStateViewModel: userStateViewModel,
        loginUser: loginUser
    }
})();

var viewModel1 = kendo.observable({
    label: 'ViewModel1',
    isLoggedInVM1: function() {
        return userState.userStateViewModel.get("isLoggedIn");
    },
    logIn: function ()
    {
        //when calling LoginUser from here, the binding is not updated, even though the value is changed (true)
        userState.loginUser();
        alert('After Login viewModel1.isLoggedInVM1() = ' + viewModel1.isLoggedInVM1() + ' but the binding has not updated');
    }  

});

alert('Value onLoad = ' + viewModel1.isLoggedInVM1());

//If you uncomment this and call LoginUser from here then afterwards the binding changes to true, but not if you call it from within ViewModel1
//userState.loginUser();


kendo.bind($("#testForm"), viewModel1);

When I call userState.loginUser() to change the value of isLoggedIn in userStateViewModel it does not update. Run and click on the button to see the problem - the binding does not reflect the updated value (but the alert box does). Any help appreciated, thank you.

Note: This is en extension of an earlier question which got me a bit further.

Answer 1

The problem is that userState is a simple object, not an ObservableObject. Because of this, the change event of the userStateViewmodel observable does not trigger the change event for viewmodel1 and the view doesn't update.

You can remedy this by making userState a property of viewModel1, so it is wrapped in an observable (or you could wrap your return object in the IIFE in an observable):

var viewModel1 = kendo.observable({
    label: 'ViewModel1',
    userState: userState,
    isLoggedInVM1: function() {
        return userState.userStateViewModel.get("isLoggedIn");
    },
    logIn: function ()
    {
        userState.loginUser();
    }          
});

Take a look at this demo; try commenting the userState property and you'll see the difference.