Xamarin Forms are the most exciting library to come along in a long time; certainly for mobile programmers. 

They bring a whole new option to cross platform development: an abstraction layer that lets you write once, and run native on each of the platforms. 

Write Once, Render Natively

This means, for example, when you create a tab page, it is rendered as a native tab page on iOS, Android and Windows Phone.  This is accomplished using pre-defined elements each of which has a hidden renderer for each platform.  Most of the time you don’t know or care how it is done, unless you want to create a custom (or customized) control.

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In yesterday’s post we looked at using HTTP with Web Forms and creating a list of blog posts from an RSS feed. Today we’ll add the ability to tap on one entry in the list and see that blog post in a viewer on the phone.

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The image shown here, incidentally, is an exact reflection of what is running on my iPhone thanks to a very handy utility named Reflector.  You run reflector and then use AirPlay on the phone to mirror what is on your phone onto the screen.

This is part of the on-going series of posts on Learning Xamarin; a complete index to the series can be found here.

This addition to our program is shockingly easy. Continued here.

Let’s say we’re building an application, and we want to list the titles and publication dates from an RSS feed. 

We can do this using a ListView, but we have to get the feed, and to do that we need a library; specifically the NuGet package Microsoft.Http.Client Libraries. 

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This is part of the on-going series of posts on Learning Xamarin; a complete index to the series can be found here.

To create our application we’ll start with a new Forms application by firing up Xamarin Studio and selecting New Solution ->  C# -> Mobile Apps -> Blank App (Xamarin.Forms.Portable

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Until now, our application has used simple “push” navigation, creating a stack that the user can pop out of to return to the calling screen. 

It would be convenient, however, to add tabs to the opening screen where the user can access the help file and the license information.

In the figure to the right, you can see that there are three tabs, and the currently selected tab is “help.”

To accomplish this, we’ll add three new pages:

• MainPage will hold the tabs
• HelpPage will hold the help text
• LicensePage will hold the license information

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The application that I began describing here (and which is part of this series) is almost done. 
Today, we’ll add a new first page to allow the user to track more than one appliance type.  This will require minor changes throughout the application and a change to the database. 
The key concern would be that we already have data in the database and now I not only want to add a table, but I want to add a property to one of the existing (and populated!) tables. 
Turns out that SQLite.net makes this a total non-issue, handling the update perfectly with no effort on my part.

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Virtually every interesting application deals with data, and very often you want that data to survive your session with the app, so that you can return to it next time.  

To accomplish this, you must write your data somewhere, and with mobile apps you have a number of options.  For small amounts of data you may well decide to write to the file system (yes, there is one!)

But for larger amounts of data, a database is very convenient, and happily SQLite comes preinstalled on iOS and Android.

Even better, nearly all the code you write for SQLite is shareable across platforms; the only platform-specific code is configuring the db connection and setting the location of the db file. 

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This is part of the on-going series of posts on Learning Xamarin; a complete index to the series can be found here.  In the previous installment, I modified the application that I began in this posting.

Today, I’m going to tinker a bit more, though the really big fix is to add persistence.  That, I’m afraid, will wait a little while longer.

What I want to do today is to ensure that the criteria are the same across items (and turn them into labels rather than values that can be filled in).  And I want to get rid of the pre-created data and make sure that my first item and first criterion work as expected.

To do this, I need to make a few modifications to the pages, but for this short posting, I’m not changing the basic structure of the program. 

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