The previous post explained what I mean by "Basic Back-End Services".
If you look at Silverlight 1.1 Alpha (or at the September Refresh of the Alpha release), you will see that it has a way of creating such services. A code sample can be found here. The idea is that you create a service just like you would create an ASP.NET AJAX service, then create a proxy using the slwsdl.exe tool, and then use the proxy to talk to your service.
However, what you see in the Alpha is a temporary solution. The main purpose of it was to show that service consumption is possible in 1.1, but the eventual solution will look different. If you are doing anything with services in 1.1, I urge you read future posts on this blog to find out what will change.
Oct 25, 2007
Introducing Basic Back-End Services: From AJAX to Silverlight
My previous post describes the overall problem of communicating with services from Silverlight. Let's now concentrate on one specific but very important part of it: "basic back-end services" (and by the way, if you can think of a better name for this please let me know :)
What I mean by "basic back-end services" is services that you write specifically for your Silverlight app.
Let's take an example: Suppose you want to create an interactive shopping application (something like this or even this). Your users will search for products, add them to a shopping cart, enter payment information, and so on. Clearly some information needs to flow between the browser and the back-end server for this to work.
Traditionally (in the pre-AJAX world) if you wanted to do this on the Microsoft platform, you would create a bunch of .aspx pages in ASP.NET that would communicate with the server using postbacks. When a user entered a search string and hit "Search", it would generate a POST to the server, which would then respond with a newly-generated page.
AJAX eliminated the need for page refreshes, and introduced the notion of "back-end services". These services process very specific information and return very specific replies instead of resending the entire page after every request. In this model, when the user hits "Search", a request is sent to the back-end service which replies with just the search results (instead of an entire HTML page that happens to contain the results). It is the job of JavaScript code to then integrate these results with the rest of the page.
Again, if we look at the Microsoft platform, ASP.NET AJAX makes this very easy with the UpdatePanel control: you don't need to write any code and you don't have to even know that these back-end services are there - you can think of them as being created automatically for you.
There are limits to what the UpdatePanel can do, and so to get more flexibility you will need to write custom services (and the JavaScript code that uses them) yourself. With ASP.NET AJAX, there are different options to write them (page methods, .asmx services, WCF services), but it all essentially boils down to the same thing: you are using JavaScript to remotely call a method. The "Search" button on your shopping site will essentially call something like GetProductList("searchString") on your back-end server, "Add To Cart"will call something like AddToCart(productId), and so on.
Notice that these back-end methods are very specific to your particular application - they are normally written specifically for this purpose and not reused for anything else. This is exactly the basic back-end services that this post is about. The opposite of this case is the interoperability problem - talking to services that have already been established for purposes other than your specific application and that you cannot change - but I will cover that separately.
So how do basic back-end services work in Silverlight? Well, in 1.0 you cannot call them from within the Silverlight app itself - your only option is to use JavaScript on the page that hosts your Silverlight control and use all of the AJAX techniques I described above.
In 1.1, you will be able to call services directly from .NET code in your Silverlight application. I will explain how in the next post.
What I mean by "basic back-end services" is services that you write specifically for your Silverlight app.
Let's take an example: Suppose you want to create an interactive shopping application (something like this or even this). Your users will search for products, add them to a shopping cart, enter payment information, and so on. Clearly some information needs to flow between the browser and the back-end server for this to work.
Traditionally (in the pre-AJAX world) if you wanted to do this on the Microsoft platform, you would create a bunch of .aspx pages in ASP.NET that would communicate with the server using postbacks. When a user entered a search string and hit "Search", it would generate a POST to the server, which would then respond with a newly-generated page.
AJAX eliminated the need for page refreshes, and introduced the notion of "back-end services". These services process very specific information and return very specific replies instead of resending the entire page after every request. In this model, when the user hits "Search", a request is sent to the back-end service which replies with just the search results (instead of an entire HTML page that happens to contain the results). It is the job of JavaScript code to then integrate these results with the rest of the page.
Again, if we look at the Microsoft platform, ASP.NET AJAX makes this very easy with the UpdatePanel control: you don't need to write any code and you don't have to even know that these back-end services are there - you can think of them as being created automatically for you.
There are limits to what the UpdatePanel can do, and so to get more flexibility you will need to write custom services (and the JavaScript code that uses them) yourself. With ASP.NET AJAX, there are different options to write them (page methods, .asmx services, WCF services), but it all essentially boils down to the same thing: you are using JavaScript to remotely call a method. The "Search" button on your shopping site will essentially call something like GetProductList("searchString") on your back-end server, "Add To Cart"will call something like AddToCart(productId), and so on.
Notice that these back-end methods are very specific to your particular application - they are normally written specifically for this purpose and not reused for anything else. This is exactly the basic back-end services that this post is about. The opposite of this case is the interoperability problem - talking to services that have already been established for purposes other than your specific application and that you cannot change - but I will cover that separately.
So how do basic back-end services work in Silverlight? Well, in 1.0 you cannot call them from within the Silverlight app itself - your only option is to use JavaScript on the page that hosts your Silverlight control and use all of the AJAX techniques I described above.
In 1.1, you will be able to call services directly from .NET code in your Silverlight application. I will explain how in the next post.
Oct 24, 2007
Talking to the Outside World from Silverlight 1.1: An Introduction
(This post is basically a recap of the introduction part of my REMIX 07 Boston Talk )
Silverlight applications run in the user's browser. We all know about the rich graphics and interactivity that Silverlight provides. But any real-world application will, at some point, need to communicate with the "outside world".
This interaction can take many forms. The simplest one (at least from a developer's point of view) is accessing media from some remote server: you can display an image or play a video from any URL. This capability exists even in the 1.0 version of Silverlight. However, it is limited to only certain types of data - images, videos and sounds.
The next step up is being able to work with arbitrary blobs of data and then write code to make sense of them. In 1.0, your only option was to use JavaScript on the page that hosts your Silverlight control. You could use standard AJAX techniques: use XmlHttpWebRequest to GET any data from some HTTP location and then use JavaScript to adjust your Silverlight graphics accordingly. You could also POST any data to some HTTP location.
In 1.1, there is no need for external JavaScript - you can use the BrowserHttpWebRequest .NET class (a subclass of HttpWebRequest) directly from your Silverlight application to issue GET/POST requests with a Stream of bytes.
But what if you want to work with more than just bytes? Most data has some structure to it: You may be receiving data in XML or JSON format that you will want to parse, or getting an RSS feed that you want to process and then display, or you may be talking to a SOAP service that actually describes its structure using metadata. In other words, you are not just working with bytes but with products, search results or high scores - data that matters to your app. The data may come from a service you yourself create, or from some "mashup-friendly" source like Flickr or Facebook.
This is exactly the problem I am working on within the overall Silverlight effort, and what many of the posts here will be about - how do we make it easy to work with structured data - that is, how do you consume "services" (in the widest sense of the word)? Watch this blog to discover what is planned in this space, and of course leave comments if you have any ideas or feedback!
I should note that most of the information here will be about SL1.1. In the existing SL1.0 (and in 1.1 as well of course) you can use all of the usual AJAX techniques as I already mentioned. In fact, Fritz Onion did a great talk at REMIX on integrating Silverlight 1.0 with ASP.NET AJAX - you can do some pretty powerful things with this combination - check out the Channel9 videos (Parts 1 2 3 4) and sample code.
Silverlight applications run in the user's browser. We all know about the rich graphics and interactivity that Silverlight provides. But any real-world application will, at some point, need to communicate with the "outside world".
This interaction can take many forms. The simplest one (at least from a developer's point of view) is accessing media from some remote server: you can display an image or play a video from any URL. This capability exists even in the 1.0 version of Silverlight. However, it is limited to only certain types of data - images, videos and sounds.
The next step up is being able to work with arbitrary blobs of data and then write code to make sense of them. In 1.0, your only option was to use JavaScript on the page that hosts your Silverlight control. You could use standard AJAX techniques: use XmlHttpWebRequest to GET any data from some HTTP location and then use JavaScript to adjust your Silverlight graphics accordingly. You could also POST any data to some HTTP location.
In 1.1, there is no need for external JavaScript - you can use the BrowserHttpWebRequest .NET class (a subclass of HttpWebRequest) directly from your Silverlight application to issue GET/POST requests with a Stream of bytes.
But what if you want to work with more than just bytes? Most data has some structure to it: You may be receiving data in XML or JSON format that you will want to parse, or getting an RSS feed that you want to process and then display, or you may be talking to a SOAP service that actually describes its structure using metadata. In other words, you are not just working with bytes but with products, search results or high scores - data that matters to your app. The data may come from a service you yourself create, or from some "mashup-friendly" source like Flickr or Facebook.
This is exactly the problem I am working on within the overall Silverlight effort, and what many of the posts here will be about - how do we make it easy to work with structured data - that is, how do you consume "services" (in the widest sense of the word)? Watch this blog to discover what is planned in this space, and of course leave comments if you have any ideas or feedback!
I should note that most of the information here will be about SL1.1. In the existing SL1.0 (and in 1.1 as well of course) you can use all of the usual AJAX techniques as I already mentioned. In fact, Fritz Onion did a great talk at REMIX on integrating Silverlight 1.0 with ASP.NET AJAX - you can do some pretty powerful things with this combination - check out the Channel9 videos (Parts 1 2 3 4) and sample code.
First Post
I decided to move my blog here (from http://blogs.msdn.com/eugeneos/), but more importantly I decided to actually start blogging (my previous blog had all of 3 posts in its 1.5 years of existence :) I work at Microsoft and currently own the web service consumption space in Silverlight 1.1, so I am sure there'll be lots of interesting things to post. Watch this space!
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