如何在 Xamarin 中从 Android 调用 SQL Server 存储过程

Question

We have a mobile application made in VB.NET for Windows CE/Mobile smart devices for shipping/reception operations in a warehouse. This application connects to a SQL Server and extensively uses stored procedures. Since Windows Mobile devices are discontinued and replaced by Android devices, we have to convert our solution to Android, using Visual Studio's Xamarin and C#.

I'm a newbie at Android programming. Is there a way we can connect directly to a SQL Server instance and call a stored procedure from Android? I made some searches and people says it's better to call web services as an intermediary between Android and SQL Server. Is it the best practice?

Thanks for your insight and help

Answer 1

Upgrading Legacy applications can be incredibly complicated depending on the technology and frameworks used.

The first thing I would suggest taking a look at is the Architecture documentation Microsoft produced for Xamarin and Cross-platform frameworks which you can see here

Typical Application Layers

• Data Layer – Non-volatile data persistence, likely to be an SQLite database but could be implemented with XML files or any other suitable mechanism.

• Data Access Layer – Wrapper around the Data Layer that provides Create, Read, Update, Delete (CRUD) access to the data without exposing implementation details to the caller. For example, the DAL may contain SQL statements to query or update the data but the referencing code would not need to know this.

• Business Layer – (sometimes called the Business Logic Layer or BLL) contains business entity definitions (the Model) and business logic. Candidate for Business Façade pattern.

• Service Access Layer – Used to access services in the cloud: from complex web services (REST, JSON, WCF) to simple retrieval of data and images from remote servers. Encapsulates the networking behavior and provides a simple API to be consumed by the Application and UI layers.

• Application Layer – Code that's typically platform specific (not generally shared across platforms) or code that is specific to the application (not generally reusable). A good test of whether to place code in the Application Layer versus the UI Layer is (a) to determine whether the class has any actual display controls or (b) whether it could be shared between multiple screens or devices (eg. iPhone and iPad).

• User Interface (UI) Layer – The user-facing layer, contains screens, widgets and the controllers that manage them.

Now you could just simply use the System.Data.SqlClient assembly and fire off stored procedure runs against your database. However a more common approach would to create an REST Api that sits in-between your client and your back-end services.

You can download a handy E-book created by the Devs over at microsoft that will show you some common enterprise patterns to use for Cross-platform technologies like Xamarin which can be found here

Here's one such example of the kind of patterns those links refer to.

You can also find an overview of various web services that you can use at this link

The options it gives you an overview of are:

• ASMX
• WCF
• REST

So plenty of choice, but depends on your current approach.