Web

Microsoft.Rest.ServiceClient opt out retry

If you use Swagger generated REST proxies then you have probably come across the pretty new Microsoft.Rest namespace and namely the abstract class ServiceClient. I noticed a strange behavior when using clients that subclass this base class. The default behavior for this class is to retry when a 500 status code is returned.
I can not understand the reason for this being Opt out, its obvious a feature like this should be Opt in. So keep in mind when using this class you must always call SetRetryPolicy to disable the retry strategy.

var service = new MyService(uri, credentials);
service.SetRetryPolicy(new RetryPolicy(new HttpStatusCodeErrorDetectionStrategy(), 0));

Client server event aggregation with Angular

I dont fancy Angular much, its slow and Knockout with its MVVM approach is much cleaner, and faster since computed and observables only mutate and change view state when they actually need to (That will change with Angular 2.0). Anyway, my current customer sports Angular and then you just have to form inline 😀 We needed immediate update and you know I love event aggregation and probably know that I have a library for it, you can read more about it here!

I created a little wrapper for the the vanilla javascript client, install it using nuget
Install-Package SignalR.EventAggregatorProxy.Client.Angular

Basically it works by extending the Angular $rootScope and adds a eventAggregator function to all scopes. The eventAggregator function resolves the scope and then creates a closure with two methods, subscribe and publish. You can now listen to a event like (Serverside or client side event).

$scope.eventAggregator().subscribe(MyApp.MyEvent, onEvent);

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MVC Custom errors, HTTP status codes and SecurityException

We use Windows Identity Foundation in my current project. WIF introduced the Claim based authorization in .NET 4.5 which is a welcomed addition since we were forced to use outdated tools like EnterpriseLibraries Rule authorization to achieve something similar before it.

Whenever a claim is not met WIF will throw a System.Security.SecurityException exception which will not play nicely with MVC Custom errors because it will render a status 500 instead of the correct status 403. This is not very user friendly since the user will think something is wrong instead of understanding that he or she needs to order additional privileges to access said part of the system.

The solution is really simple and I did not find it when googling, thus this blog post 😀 (more…)

Seperate KO View formating and ViewModel state

A normal scenario with Knockout is that you want date and number observables to be formatted to the current culture of the client, this is easily implemented in a Knockout extender, something like.

ko.extenders.numeric = function(observable, options) {
    var textValue = null;
    return ko.computed({
        write: function(value) {
            textValue = value;
            var parsed = Number.parseFloat(value);
            if(!isNaN(parsed)) {
                observable(parsed);
            } else {
                observable(null);
            }
        },
        read: function() {
            var value = observable();
            if(value == null) {
                return textValue;
            }

            return value.toLocaleString(); //This  can be replaced with for example the Globalize plugin 
        }
    });
};

Use it like

this.amount = ko.observable().extend({ numeric: true });

The problem with this approach is that the ViewModel will no longer work against numbers it will work against formatted strings, so this.amount() will return a string instead of a number. This is very bad practice in a View/ViewModel seperation stand point. (more…)

Single Page Application with Sub-routing

One of my colleagues is working on a Single Page Application, he asked me for help on a solid design for routing and specifically about sub-routing. Sub-routing in a SPA is complex, as an example when you click a link in a list you want that item to be presented in a modal window. If you close the modal window and press back in the history you want it to show again, and if you press forward you want it to close. I choose to attack this problem with an Event Aggregation approach, where changes to the route resulted in a change event being fired to any listener. (more…)

Wrap client side code in a Web Forms Control

I’m currently between assignments and in the meantime I’m helping fellow colleagues with a Web Forms system. They needed a Combobox for a requirement and after some googling I found out that there is none for free which suits their needs. I have created a Knockout enabled combo called Knockout.Combobox. I decided to take this client side combobox and wrap it in a Web Forms Control.
(more…)

Client – server event aggregation with SignalR

Event aggregation is really a pattern i like, there is something elegant about firing events and subscribers can listen to them without knowing who fired them. This creates decoupled domains both in backends and frontends. At my latest customer we saw an increasing demand for pub / sub and immediate update. We fired events on the backend event bus and in the frontend we had SignalR Hubs that picked up the events and forwarded them to the clients. This caused duplicated and similar code both on the client and on the web server. I decided to create an abstraction layer between SignalR and the event aggregator. The result is a library called SignalR.EventAggregatorProxy

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Why overriding JsonSerializer no longer work in SignalR 2.0

I see almost everyday people having problem with overriding JSON serializer settings in SignalR. In SignalR 1.x they used an interface, IJsonSerializer, that you could override to set the JSON settings. In SignalR 2.x they instead use a concrete type JsonSerializer.

Ninject

The problem starts if you use a dependency injection framework like Ninject. The Dependency resolver that most people use for Ninject together with SignalR is doing this to get a type.

return kernel.TryGet(serviceType) ?? base.GetService(serviceType);

In SignalR 1.x this worked because when Ninject is doing TryGet on an interface it will return null and instead call base.GetService which in turn will use the type registered with SignalR’s internal IoC (GlobalHost.DependencyResolver).

In SignalR 2.x this will no longer work because we are now using a concrete type and Ninject will create instances of unregistered concrete types without complaining. base.GetService will never be called and the types registered in GlobalHost.DependencyResolver will not be used.

Remedy

One way of solving this is to register the JsonSerializer with the Ninject kernel instead of register it with GlobalHost.DependencyResolver.Register

The other is to check if the type is registered with Ninject, if it is use kernel.Get otherwise use base.GetService. This can be done like

kernel.GetBindings(serviceType).Any();

Convention based MVVM with Knockout

One of my most popular Open source projects, FreePIE, is a WPF application and it utilizes a library called Caliburn.Micro. The main idea for that library is to minimize the use of explicit declared bindings and use conventions to implicit bind to the ViewModel under the hood. As an example, if you have a button called Save and a method called Save on your VM, Caliburn.Micro will make sure these are bound.
This is a welcomed tool since XAML bindings are, to say the least, verbose.

Bindings get even more verbose in the Knockout world because of the fact that you can write inline JavaScript in the bindings, fact is the entire data-bind attribute is inline JavaScript that is executed by Knockout. I’ve seen that bindings like these and worse are common out there.

<button data-bind="enable: errors().length === 0">Save</button>

I started to write a Convention based library called Knockout.BindingConventions a year ago and I added support for Knockout 3.0 a while back. Even though the library isn’t new I thought I could write about it, it’s a good way to get to know the inner working of Knockout and also convention over configuration. (more…)