Skip to main content

How to define promises on Metro App for Windows 8 using JavaScript

Metro application from Windows 8 can be written not only in C# with XAML but also in Java Script and HTML5. As we all know we can do a lot of thinks with asynchronous programming.
In this post I want to describe how we can define asynchronous methods in Java Script. The name that is used for this kind of actions is "Promises". This can be used for operations that take a long time to complete.
A common pattern for this kind of actions is the callback pattern. Basically, when you call a method asynchron, one parameter is the callback action that is called when the action finish executing.
The definition of promises was not made my Microsoft. The CommonJS were the first one that introduces this pattern. Microsoft only adopted this pattern that is very similar to asynchronous calls of .NET library.
This pattern tries to define a common way to make asynchronous calls, in a predictable way (manner).
In a metro application, WinJS define three types of callbacks that we can use:
  • complete callback
  • failure callback
  • progress callback
When we call an asynchronous action that support promises we can specify these three types of callbacks.
 function(response){...}, // Success
 function(response){...}, // Fail
 function(status){...}) // Progress
 successMethod, // Success
 failMethod, // Fail
 progressMethod) // Progress
Many places from WinJS library use promises, from control library to animation or binding. As you can see it is very easy to use promises, but let see what we can define our own promises. In the next example we use the timeout function:
    function(){console.log("progress change")}
To be able to create our own promises we need to create our own instance of a Promise object
The constructor of a WinJS.Promise class accepts our three callbacks: success, fail and progress. In our implementation we need only to call our functions.
function someMethod() {
        return new WinJS.Promise(function (complete, error, progress) {
            // Some async calls
In our case, the call to our class could look something like this:
var request = sommeMethod()
   function() { console.log("done"); },
   function() { console.log("failed"); },
   function() { console.log("progress change");
For cancelation action we don't need any kind of custom think. We only need to call the cancel method. Automatically the error method will be called.
When we are using promises we define a list of promises that we want to wait before the complete action is called. This action can be done using WinJS.Promise.join method. As the first parameter we need to define our promises. After that we can use then and define our callbacks.
WinJS.Promise.join([someMethod(), someMethod1("someParam")])
 .then(function() { console.log("done");});
If we want to end the call when one of the methods finish we would need to use WinJS.Promise.any.
WinJS.Promise.any([someMethod(), someMethod1("someParam")])
 .then(function() { console.log("done");});
When one of the calls finished, our complete method is automatically called, even if only one called is complete.
In this post we saw not only how we can use promises but how we can define them. The definition process of a promise is very simple and strait.
A post about Promises in JavaScript in a Metro Application:


Popular posts from this blog

ADO.NET provider with invariant name 'System.Data.SqlClient' could not be loaded

Today blog post will be started with the following error when running DB tests on the CI machine:
threw exception: System.InvalidOperationException: The Entity Framework provider type 'System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer' registered in the application config file for the ADO.NET provider with invariant name 'System.Data.SqlClient' could not be loaded. Make sure that the assembly-qualified name is used and that the assembly is available to the running application. See for more information. at System.Data.Entity.Infrastructure.DependencyResolution.ProviderServicesFactory.GetInstance(String providerTypeName, String providerInvariantName) This error happened only on the Continuous Integration machine. On the devs machines, everything has fine. The classic problem – on my machine it’s working. The CI has the following configuration:

TeamCity.NET 4.51EF 6.0.2VS2013
It seems that there …

GET call of REST API that contains '/'-slash character in the value of a parameter

Let’s assume that we have the following scenario: I have a public HTTP endpoint and I need to post some content using GET command. One of the parameters contains special characters like “\” and “/”. If the endpoint is an ApiController than you may have problems if you encode the parameter using the http encoder.
using (var httpClient = new HttpClient()) { httpClient.BaseAddress = baseUrl; Task<HttpResponseMessage> response = httpClient.GetAsync(string.Format("api/foo/{0}", "qwert/qwerqwer"))); response.Wait(); response.Result.EnsureSuccessStatusCode(); } One possible solution would be to encode the query parameter using UrlTokenEncode method of HttpServerUtility class and GetBytes method ofUTF8. In this way you would get the array of bytes of the parameter and encode them as a url token.
The following code show to you how you could write the encode and decode methods.

Entity Framework (EF) TransactionScope vs Database.BeginTransaction

In today blog post we will talk a little about a new feature that is available on EF6+ related to Transactions.
Until now, when we had to use transaction we used ‘TransactionScope’. It works great and I would say that is something that is now in our blood.
using (var scope = new TransactionScope(TransactionScopeOption.Required)) { using (SqlConnection conn = new SqlConnection("...")) { conn.Open(); SqlCommand sqlCommand = new SqlCommand(); sqlCommand.Connection = conn; sqlCommand.CommandText = ... sqlCommand.ExecuteNonQuery(); ... } scope.Complete(); } Starting with EF6.0 we have a new way to work with transactions. The new approach is based on Database.BeginTransaction(), Database.Rollback(), Database.Commit(). Yes, no more TransactionScope.
In the followi…