Using Java interop in your Xamarin.Android

Agenda Java interop… wait what!? Beyond basic interop Building your own interop components

JAVA INTEROP, WAIT WHAT?!

Java interop, what what?! Building an Android app in C# namespace TaskTracker.Client.Android { [Activity(Label = "TaskTracker.Client.Android", MainLauncher = true, Icon = public class Activity1 : ListActivity { private TasksOfflineContext _context; protected override void OnCreate(Bundle bundle) { base.OnCreate(bundle); _context = new TasksOfflineContext("sync", new Uri(" _context.CacheController.ControllerBehavior.SerializationFormat = SerializationFormat.ODataJSON; _context.CacheController.RefreshCompleted += OnRefreshCompleted; _context.CacheController.RefreshAsync(); }

Java interop, what what?! Meanwhile in Java country… Cross Platform Mobile Development - Android public class Activity1 extends android.app.ListActivity implements mono.android.IGCUserPeer { static final String __md_methods; static { __md_methods = "n_onCreate:(Landroid/os/Bundle;)V:GetOnCreate_Landroid_os_Bundle_Handler\n" + ""; mono.android.Runtime.register ("TaskTracker.Client.Android.Activity1, “ + “TaskTracker.Client.Android, Version= , Culture=neutral, PublicKeyToken=null", Activity1.class, __md_methods); } public Activity1 () { super (); if (getClass () == Activity1.class) mono.android.TypeManager.Activate ("TaskTracker.Client.Android.Activity1, “ + “TaskTracker.Client.Android, Version= , Culture=neutral, “ …

Java interop, what what?! Linux Kernel Mono (.NET Runtime) Dalvik (Java Runtime).NET APIs Android Bindings Android.* Java.* MCW ACW Android callable wrappers Mono callable wrappers

Java interop, wait what?! What you are essentially doing is building apps that rely heavily upon interop. In fact: Everything you build on Android will at some point talk to a piece Java code. Cross Platform Mobile Development - Android

Java interop, wait what?! So why not take advantage of the situation? – You can extend your app with Java code – Found a cool Android library? Bind it! Cross Platform Mobile Development - Android

BEYOND BASIC INTEROP

Beyond basic interop The two-way traffic between Android and Mono is done through two endpoints: – Mono  Java Mono Callable Wrappers – Java  Mono Android Callable Wrappers Cross Platform Mobile Development - Android

Beyond basic interop - MCWs Linux Kernel Mono (.NET Runtime) Dalvik (Java Runtime).NET APIs Android Bindings Android.* Java.* MCW ACW

Beyond basic interop – MCWs Talking to Java from.NET is done through the Java Native Interface – The next bit is going to get pointy or pointerific depending on what you like… Cross Platform Mobile Development - Android

MCW INTERNALS Demo Cross Platform Mobile Development - Android

Beyond basic interop – MCWs Steps to create an instance of a Java class – Find the handle to the type – Marshal constructor arguments – Invoke the constructor – Safe the instance pointer! Cross Platform Mobile Development - Android

Beyond basic interop – MCWs Steps to invoke a Java method: – Find the handle to the method – Marshal the arguments – Invoke the method Cross Platform Mobile Development - Android

Beyond basic interop – MCWs Notice the TransferOwnership settings – Important, who is the owner of the handle? – Care must be taken when transferring handles – If two objects own a handle, the app will be unstable! Cross Platform Mobile Development - Android

Beyond basic interop – MCWs Important to know: – When invoking JNI, native handles are used – Has effect on garbage collection, so clean it up! – Please, Reduce the amount of memory copy actions, it will improve the performance. Cross Platform Mobile Development - Android

Beyond basic interop - ACWs Linux Kernel Mono (.NET Runtime) Dalvik (Java Runtime).NET APIs Android Bindings Android.* Java.* MCW ACW

ACW INTERNALS Demo Cross Platform Mobile Development - Android

Beyond basic interop - ACWs Android callable wrappers are the least of your problems. – Generated by the Mono compiler – Don’t touch or you will break them! Cross Platform Mobile Development - Android

Performance considerations A few things you need to know: – Value types are copied between Java and Mono – For reference types pointers are exchanged – 4 bytes in.NET != 4 bytes in Java, sometimes Cross Platform Mobile Development - Android Beware Bitmap users!

BUILDING YOUR OWN INTEROP

Building your own interop Explicit use of interop is possible from your own app through these methods: – Add Java source files to your project – Create bindings for an existing library Cross Platform Mobile Development - Android

Adding Java sources Add a.java file to your project for – You found an activity or service that you don’t want to translate to.NET code – You have a single component, but not enough to create a library (Please keep it to one file). Cross Platform Mobile Development - Android

ADDING JAVA SOURCES Demo Cross Platform Mobile Development - Android

Binding Java libraries This is the real stuff, the big one, the goodest. – Allows you to use existing libraries – Automatically generates wrappers for Java classes based on the settings you provide. Cross Platform Mobile Development - Android

Binding Java libraries The steps for binding a Java library: 1.Add the Java library to the binding project 2.Customize the transformations 3.Extend the library with your own goodies Cross Platform Mobile Development - Android

Binding Java libraries The steps for binding a Java library: 1.Add the Java library to the binding project 2.Customize the transformations 3.Extend the library with your own goodies Cross Platform Mobile Development - Android

BINDING A JAVA LIBRARY Demo Cross Platform Mobile Development - Android

Binding Java libraries The steps for binding a Java library: 1.Add the Java library to the binding project 2.Customize the transformations 3.Extend the library with your own goodies Cross Platform Mobile Development - Android

CUSTOMIZING TRANSFORMATIONS Demo Cross Platform Mobile Development - Android

Binding Java libraries The steps for binding a Java library: 1.Add the Java library to the binding project 2.Customize the transformations 3.Extend the library with your own goodies Cross Platform Mobile Development - Android

EXTENDING BINDINGS Demo Cross Platform Mobile Development - Android

Final thoughts Java interop is all around you in Xamarin.Android – Don’t worry too much about it in your day-to-day Android development. – Use it when you need it, to get more power! Cross Platform Mobile Development - Android