Durandal Custom View Location Strategy - durandal

Question

I am trying to figure out how to use a custom view location strategy, I have read the documentation at this page http://durandaljs.com/documentation/Using-Composition/ but I don't exactly understand what the strategy function should look like.
Can anybody give me a quick example of what the implementation of this function would be like and the promise that returns (even a simple one) etc?
Thanks in advance,
Gary
p.s. This is the code in my html:
<div>
<div data-bind="compose: {model: 'viewmodels/childRouter/first/simpleModel', strategy:
'viewmodels/childRouter/first/myCustomViewStrategy'}"></div> </div>
and this is the code in my myCustomViewStrategy:
define(function () {
var myCustomViewStrategy = function () {
var deferred = $.Deferred();
deferred.done(function () { console.log('done'); return 'simpleModelView'; });
deferred.fail(function () { console.log('error'); });
setTimeout(function () { deferred.resolve('done'); }, 5000);
return deferred.promise();
};
return myCustomViewStrategy;
});
but I get the error:
Uncaught TypeError: Cannot read property 'display' of undefined - this is after done has been logged in the console window.

Answer 1

Okay I solved this by creating my custom view strategy by the following:
define(['durandal/system', 'durandal/viewEngine'], function (system, viewEngine) {
var myCustomViewStrategy = function () {
return viewEngine.createView('views/childRouter/first/sModelView');
}
return myCustomViewStrategy;
});

Answer 2

As I found the documentation a bit lacking on compose binding's strategy setting I checked the source code how it works. To summ it up:
The module specified by the compose binding's strategy setting by its moduleId
must return a function named 'strategy'
which returns a promise which results in the view to be bound
as a HTML element object.
As a parameter the strategy method receives the compose binding's settings object
with the model object already resolved.
A working example:
define(['durandal/system', 'durandal/viewEngine'], function (system, viewEngine) {
var strategy = function(settings){
var viewid = null;
if(settings.model){
// replaces model's module id's last segment ('/viewmodel') with '/view'
viewid = settings.model.__moduleId__.replace(/\/[^\/]*$/, '/view');
}
return viewEngine.createView(viewid);
};
return strategy;
});
Durandal's source:
// composition.js:485
for (var attrName in settings) {
if (ko.utils.arrayIndexOf(bindableSettings, attrName) != -1) {
/*
* strategy is unwrapped
*/
settings[attrName] = ko.utils.unwrapObservable(settings[attrName]);
} else {
settings[attrName] = settings[attrName];
}
}
// composition.js:523
if (system.isString(context.strategy)) {
/*
* strategy is loaded
*/
system.acquire(context.strategy).then(function (strategy) {
context.strategy = strategy;
composition.executeStrategy(context);
}).fail(function(err){
system.error('Failed to load view strategy (' + context.strategy + '). Details: ' + err.message);
});
} else {
this.executeStrategy(context);
}
// composition.js:501
executeStrategy: function (context) {
/*
* strategy is executed
* expected to be a promise
* which returns the view to be bound and inserted to the DOM
*/
context.strategy(context).then(function (child) {
composition.bindAndShow(child, context);
});
}