At NDC London, Jon and K. Scott talk to Paul Betts about several of his recent open source libraries designed to simplify cross platform development on C#.
- (00:18) Jon welcomes Paul back – he’s been on a few times before, talking about GitHub for Windows and Reactive UI.
- (00:28) Paul has a dream: he’d like to write applications in C# and have them run everywhere: iOS, Android, Windows Phone maybe even WinRT. He’s not interested in sharing everything (views or designer code), but there’s plenty of other code that developers shouldn’t need to rewrite for every platform.
- (01:16) Jon asks if Xamarin doesn’t help with this. Paul says that Xamarin’s intention is to give you direct access to the native platform, which is good when developing for a specific platform, but not when you’re working on cross-platform applications.
- 01:32 Paul’s been on a crusade, writing a lot of small, cross-platform libraries.
- (01:48) splat is a library that lets you share certain things in cross-platform viewmodels, the biggest one being images. It allows for the simple load-and-display scenario. Each platform hast its own image types; splat gives you a common abstract image type that you can then cast to a native image. This allows you to write cross-platform viewmodels and just have native views. splat also gives you System.Drawing on platforms that don’t have it, e.g. WinRT by providing common types for primitives like colors and rectangles.
- (04:08) Jon asks if portable class libraries will help with this. Paul explains the PCL operations for splat.
- (04:45) Jon asks about support for high-DPI / Retina images. Paul talks about how the different platforms handle high DPI images.
- (05:44) Paul says that HttpClient is implemented on Xamarin using HttpWebRequest. This has some problems: it doesn’t use 3G on iOS, and it’s a blocking call. That means if you make several web requests, you end up with a bunch of waiting threads and the app slows down.
- (06:45) There are better APIs available on each platform, so Paul’s taken the most popular HTTP libraries on each platform and made them HttpClient compatible. HttpClient allows you to specify an HttpMessageHandler, so in your portable library you can just drop in the handlers provided by ModernHttpClient .
- (08:33) In the latest version, Paul’s done work to make sure you can cancel requests. This lets you cancel a request based on headers (e.g. status codes or ETags) which can make a big difference on mobile network usage.
- (09:23) Jon asks how it works in the Windows platforms. Paul says that on WinRT it’s already built in, and on Windows Phone there’s no way to do anything better than HttpWebRequest.
- Jon asks a bit more about how you use it. Paul explains how platform-specific factory methods can provide the different handlers.
- (11:00) punchclock lets you make multiple web requests; it queues them up and makes the requests for you so there are a maximum of four web requests at a time. It’s based on an Android library called Volley.
- (12:20) punchclock is a priority based scheduler. You can then make things like analytics low priority and user initiated requests high priority.
- (13:12) It’s not just specific to network requests, you can use it for anything that’s awaitable.
- What’s Paul using these on?
- (13:35) Jon asks Paul what kind of mobile applications he’s building that are pushing him to build these libraries. Paul says he’s been working on some internal applications at GitHub. One example is a support application called Halp. It lets customer support people use @mention style messages to developers, allowing developers to respond quickly from mobile devices.
- Reactive UI documentation
- (15:10) Jon asks Paul what he’s been doing when he’s not writing cool code. Paul says he’s been working on documentation for Reactive UI by writing one big article per day.