WinJS variable/object scope, settings, and events? - windows-runtime

Question

I am not sure what the proper heading / title for this question should be. I am new to WinJS and am coming from a .NET webform and winclient background.
Here is my scenario. I have a navigation WinJS application. My structure is:
default.html
(navigation controller)
(settings flyout)
pages/Home.html
pages/Page2.html
So at the top of the default.js file, it sets the following variables:
var app = WinJS.Application;
var activation = Windows.ApplicationModel.Activation;
var nav = WinJS.Navigation;
It seems like I cannot use these variables anywhere inside my settings flyout or any of my pages:ready functions. They are only scoped to the default.js?
In the same regard, are there resources on the interwebs (links) that show how to properly share variables, events, and data between each of my "pages"?
The scenario that I immediately need to overcome is settings. In my settings flyout, I read and allow the user to optionally set the following application setting:
var applicationData = Windows.Storage.ApplicationData.current;
var localSettings = applicationData.localSettings;
localSettings.values["appLocation"] = {string set by the user};
I want to respond to that event in either my default.js file or even one of my navigation pages but I don't know where to "listen". My gut is to listen for the afterhide event but how do I scope that back to the page where I want to listen from?

Answer 1

Bryan. codefoster here. If you move the lines you mentioned...
var app = WinJS.Application;
var activation = Windows.ApplicationModel.Activation;
var nav = WinJS.Navigation;
...up and out of the immediate function, they'll be in global scope and you'll have access to them everywhere. That's one of the first things I do in my apps. You'll hear warnings about using global scope, but what people are trying to avoid is the pattern of dropping everything in global scope. As long as you control what you put in there, you're fine.
So put them before the beginning of the immediate function on default.js...
//stuff here is scoped globally
var app = WinJS.Application;
var activation = Windows.ApplicationModel.Activation;
var nav = WinJS.Navigation;
(function () {
//stuff here is scoped to this file only
})();
If you are saving some data and only need it in memory, you can just hang it off the app variable instead of saving it into local storage. That will make it available to the whole app.
//on Page2.js
app.myCustomVariable = "some value";
//on Page3.js
if(app.myCustomVariable == "some value") ...

Answer 2

Regarding your immediate need:
like mentioned in the other answer, you can use datachanged event.
Regards sharing variables:
If there are variables that you would like to keep global to the application, they can be placed outside the anonymous function like mentioned in the Jeremy answer. Typically, that is done in default.js. Need to ensure that scripts using the global variables are placed after the script defining the global variable - in default.html. Typically - such variable will point to singleton class. For example: I use it in one of my apps to store authclient/serviceclient for the backend service for the app. That way - the view models of the multiple pages need not create instance of the object or reference it under WinJS namespace.
WinJS has also concept of Namespace which lets you organize your functions and classes. Example:
WinJS.Namespace.define('Utils.Http',
{
stringifyParameters: function stringifyParameters(parameters)
{
var result = '';
for (var parameterName in parameters)
{
result += encodeURIComponent(parameterName) + '=' + encodeURIComponent(parameters[parameterName]) + '&';
}
if (result.length > 0)
{
result = result.substr(0, result.length - 1);
}
return result;
},
}
When navigating to a page using WinJS.Navigation.navigate, second argument initialState is available as options parameter to the ready event handler for the page. This would be recommended way to pass arguments to the page unless this it is application data or session state. Application data/session state needs to be handled separately and needs a separate discussion on its own. Application navigation history is persisted by the winjs library; it ensures that if the app is launched again after suspension - options will be passed again to the page when navigated. It is good to keep the properties in options object as simple primitive types.
Regards events:
Typically, apps consume events from winjs library. That can be done by registering the event handler using addEventListener or setting event properties like onclick etc. on the element. Event handlers are typically registered in the ready event handler for the page.
If you are writing your own custom control or sometimes in your view model, you may have to expose custom events. Winjs.UI.DOMEventMixin, WinJS.Utilities.createEventProperties can be mixed with your class using WinJS.Class.mix. Example:
WinJS.Class.mix(MyViewModel,
WinJS.Utilities.createEventProperties('customEvent'),
WinJS.UI.DOMEventMixin);
Most often used is binding to make your view model - observable. Refer the respective samples and api documentation for details. Example:
WinJS.Class.mix(MyViewModel,
WinJS.Binding.mixin,
WinJS.Binding.expandProperties({ items: '' }));

Answer 3

Here is what I ended up doing which is kinda of a combination of all the answers given:
Created a ViewModel.Settings.js file:
(function () {
"use strict";
WinJS.Namespace.define("ViewModel", {
Setting: WinJS.Binding.as({
Name: '',
Value: ''
}),
SettingsList: new WinJS.Binding.List(),
});
})();
Added that file to my default.html (navigation container page)
<script src="/js/VMs/ViewModel.Settings.js"></script>
Add the following to set the defaults and start 'listening' for changes
//add some fake settings (defaults on app load)
ViewModel.SettingsList.push({
Name: "favorite-color",
Value: "red"
});
// listen for events
var vm = ViewModel.SettingsList;
vm.oniteminserted = function (e) {
console.log("item added");
}
vm.onitemmutated = function (e) {
console.log("item mutated");
}
vm.onitemchanged = function (e) {
console.log("item changed");
}
vm.onitemremoved = function (e) {
console.log("item removed");
}
Then, within my application (pages) or my settings page, I can cause the settings events to be fired:
// thie fires the oniteminserted
ViewModel.SettingsList.push({
Name: "favorite-sport",
Value: "Baseball"
});
// this fires the itemmutated event
ViewModel.SettingsList.getAt(0).Value = "yellow";
ViewModel.SettingsList.notifyMutated(0);
// this fires the itemchanged event
ViewModel.SettingsList.setAt(0, {
Name: "favorite-color",
Value: "blue"
});
// this fires the itemremoved event
ViewModel.SettingsList.pop(); // removes the last item

Answer 4

When you change data that needs to be updated in real time, call applicationData.signalDataChanged(). Then in the places that care about getting change notifications, listen to the datachanged on the applicationData object. This is also the event that is raised when roaming settings are synchronized between computers.
I've found that many times, an instant notification (raised event) is unnecessary, though. I just query the setting again when the value is needed (in ready for example).