Cross-platform UI Development with Xamarin.Forms:

There are quite a number of different design templates freely available for download (a quick search on https://images.google.com/ will show them). The following template will be used in this book:

For each new view, a new design will be drawn. While the app will never be a one-to-one representation of the design, it should be close and give an idea of how all sections would work together.

It is also a good idea to use piece of flowcharting software when creating a flow. Again, there are plenty of pieces available, but through trial and error, one of the best that I have found is called the yEd Graph Editor (http://www.yworks.com/en/products/yfiles/yed/).

When creating any piece of software, it's also a good plan to have a shopping list of the features that you would like to see in the final application.

The shopping list should feature everything that you want in the app rather than everything that you think should be in the app. If you have a large budget, then the shopping list can be longer. Remember, the longer the list, the larger (and more complex) the application.

The basics of any messenger application UI comprises of the following lists:

The following are a few details about the basics:

While Android is a very open platform that allows users to create their own apps for messaging, iOS is very prescriptive over what you can and cannot do. For example, to create a text message, you must use their text message service and software. This is fine, except that it ties you in strongly to what Apple provides, and doesn't give the end user any different an experience; so why should they bother using what you have over what Apple supplies?

To remove this requirement, a web service can be used. The use of the web service gives a number of advantages:

This final point is of great importance for this application.

As the name of this book includes Xamarin, and you are reading this, you will be aware that we are using C# for the core language. This will already be giving a massive advantage in terms of code sharing (for example, all the data services, SQL, and core code will be the same, irrespective of the platform), and also by using one of the more recent additions to Xamarin. It also means that the user interface can be shared by using Xamarin.Forms.

We can also swap between devices. On my desk, I have to handle a range of Android devices (tablets and phones), a couple of Windows Phones, a couple of iPhones, and an iPad. At any given time, I may have two of the phones on me, and want to use the app on either of the devices. Not only will the data structure need to be the same but ideally, a similar user interface is needed. This is not to say that each platform version cannot make use of some specific tweak on each platform, but the overall experience needs to be the same.

A secondary aspect to having a cross-platform application is to have a common settings file. All three platforms store user data in a different (and largely incompatible) way meaning that for personal data and app settings, a common profile needs to be established. This can be achieved either online, offline, or both, each having their own advantages and disadvantages:

Obviously, from a portability and usability point of view, having both as options is the best way forward; however, synchronizing changes may be an issue: which is the newer settings file?

Windows Phone, iOS, and Android all come with an implementation of SQLite (though Windows Phone does require the package to be installed via nuget). This means that we can have the same data structure for all platforms apart from being able to match up to the server with minimal issues. The code for accessing the databases will be covered in Chapter 5, Data, Generics and Making Sense of Information; here we will discuss the data table classes.

Any database can be considered as a series of disparate objects that may or may not be linked. Each of these objects is an entry in a data table.

Consider the following example of a book, author, and publisher:

The Newton-le-Willows Community Library has a hundred books on Android development. For argument's sake, they have only one edition and a single author for each book. Each book has the following information stored on it: the ISBN, price, author, publication date, and publisher.

The ISBN number is unique to each book, so it is never replicated making it perfect as what is known as a Primary Key. The author may have written any number of books (not only on Android, but possibly in Chemistry and the UK Armed Forces between 1960 and 1965, for example). A name is also not unique—I went to school with three people who had the same name as me.

The publisher too, will have a table containing information such as their address.

In terms of a database structure, the publisher and the author will have what is known as a one-to-many relationship with the book (the meaning is literally that—one publisher or author to many books) going FROM the publisher or author table TO the book. Going FROM the book TO the author or publisher shows a many-to-one relationship.

To complete this triangle, there will be a relationship between the publisher and the author. As the publisher is a single entity using multiple authors, it will have a one-to-many relationship with the authors.

The ISBN number will have a one-to-one relationship with the publisher and the author.

While it is fine to have storage on the device, there needs to be an external server somewhere. Currently, there are two main players when it comes to external servers if you are unable to host things yourself. They are Microsoft Azure and Amazon. Both offer the same sort of facilities, but given that Xamarin uses the .NET framework, it makes slightly more sense to use Azure.

The configuration and setting up of an Azure service is covered extensively in Chapter 14, Bringing It All Together.

Part of ensuring that messages get through as soon as they are sent is to use a push notification. Essentially, this is sent out from the server to the application. Unfortunately, the procedure for getting this to work is not the same for Android and iOS.

For the application to be able to access the Azure services, it requires an additional package. You can manually create it, but it is easier to use the NuGet package. I will cover this in detail in Chapter 3, Making It Pretty and Logging In.