From Objective-C to Xamarin

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From Objective-C to Xamarin First impressions and common pitfalls Alexander Dodatko 2015

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Xamarin == C# for Mobile

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Xamarin's Promise One Codebase — Many Platforms

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Native UI and UX

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http://bit.ly/ 1xV1ATx

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PCL - Portable Class Libraries A standard by M$ and Xamarin

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Your Code Runs Everywhere If a platform has .NET

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CI requires NO Simulator

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Binary Packets

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● Closures ● Optionals ● Namespaces ● Generics ● Type Safety ● Functional As Good as Swift

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You can use exceptions And you should do so

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Callback Hell http://bit.ly/ 11suEXP

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http://bit.ly/ 1ryzV4Z

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Async/Await

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public class RestApiCallFlow { public static async Task LoadRequestFromNetworkFlow ( TRequest request, IRestApiCallTasks stages) { string requestUrl = await stages.BuildRequestUrlForRequestAsync(request); // TODO : check cache THttpResult serverResponse = await stages.SendRequestForUrlAsync(requestUrl); TResult parsedData = await stages.ParseResponseDataAsync(serverResponse); return parsedData; } } Async but Looks Linear

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public class RestApiCallFlow { public static async Task LoadRequestFromNetworkFlow ( TRequest request, IRestApiCallTasks stages) { string requestUrl = await stages.BuildRequestUrlForRequestAsync(request); try { TResult parsedDataFromCache = await stages.LoadDataFromCacheForRequestAsync(request); return parsedDataFromCache; } catch { // Load from network code } } }

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public interface IRestApiCallTasks { Task BuildRequestUrlForRequestAsync(TRequest request); Task SendRequestForUrlAsync(string requestUrl); Task ParseResponseDataAsync(THttpResult httpData); Task LoadDataFromCacheForRequestAsync(TRequest request); }

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Is this lib portable?

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Same API may Work Differently

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Xamarin is Slow and has Lots of Memory Leaks From some holy war

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using (var webclient = new WebClient()) { var imageBytes = webclient.DownloadData(url); return UIImage.LoadFromData(NSData.FromArray(imageBytes)); } http://bit.ly/ 1rMJL3B Image Loading : A Typical Implementation

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using (var webclient = new WebClient()) { var imageBytes = webclient.DownloadData(url); return UIImage.LoadFromData(NSData.FromArray(imageBytes)); } http://bit.ly/ 1rMJL3B Synchronous

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using (var webclient = new WebClient()) { var imageBytes = webclient.DownloadData(url); return UIImage.LoadFromData(NSData.FromArray(imageBytes)); } http://bit.ly/ 1rMJL3B Leaks

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http://bit.ly/1 cay6bO

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http://bit.ly/1 cay6bO

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What If I Told You...

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All Obj-C/Java bindings are IDisposable

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UIImage, NSData, sockets, threads

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byte[] data = null; using (Stream response = await session.DownloadResourceAsync(request)) using (MemoryStream responseInMemory = new MemoryStream()) { await response.CopyToAsync(responseInMemory); data = responseInMemory.ToArray(); } BeginInvokeOnMainThread(delegate { using ( NSData imageData = NSData.FromArray(data) ) { using ( UIImage image = new UIImage(imageData) ) { this.ImageView.Image = image; } } }); http://bit.ly/ 1ukw1ii

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Xamarin.Forms

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Aiming for a Single Codebase

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Break their own Principles

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Unlike other cross-platform mobile frameworks that only offer lowest common denominator experiences through UI abstraction libraries, we make 100% of the iOS and Android APIs available through our native bindings.