by Miguel de Icaza

Today we are happy to release Mono for Android 1.0 as well as MonoTouch 4.0.

Both products allow you to use the C# language to write applications that run on Android and iOS devices.

Both products are based on the latest Mono 2.10 core. The Parallel Frameworks can be used to write more elegant multi-threaded code across all devices, and automatically takes advantage of multiple cores available on the iPad2 and Xoom devices. The C# 4.0 is now the default as well as the .NET 4.0 APIs.

Mono for Android

Our Mono for Android debuts today after almost a year worth of development.

Perhaps the most important lesson that we got from MonoTouch's success was that we had to provide a completely enabled platform. What we mean by this is that we needed to provide a complete set of tools that would assist developers from creating their first Android application, to distributing the application to the market place, to guides, tutorials, API documentation and samples.

Mono for Android can be used from either Visual Studio Professional 2010 for Windows users, or using MonoDevelop on the Mac.

Mono code runs side-by-side the Dalvik virtual machine in the same process:

This is necessary since code running in Dalvik provides the user interface elements for Android as well as the hosting and activation features for applications on Android.

APIs

The Mono for Android API is made up of the following components: Core .NET APIs, Android.* APIs, OpenGL APIs and Java bridge APIs.

Let us start with the most interesting one: Android.* APIs. These are basically a 1:1 mapping to the native Java Android APIs but they have been C#-ified, for example, you will find C# properties instead of set/get method calls, and you will use C# events with complete lambda support (with variables being automatically captured) instead of Java inner classes. This means that while in Java you would write something like:

// Java code button.setOnClickListener (new View.OnClickListener() { public void onClick(View v) { button.setText ("Times clicked: " + Integer.toString(counter)); } });

// C# code button.Click += delegate { button.Text = "Times clicked: " + counter; };

In addition to the UI APIs, there are some 57 Android.* namespaces bound that provide access to various Android features like telephony, database, device, speech, testing and many other services.

In what is becoming the standard in the Mono world, OpenGL is exposed through the brilliant OpenTK API. OpenTK is a strongly typed, Framework Design Guidelines-abiding binding of OpenGL. The benefit is that both Visual Studio and MonoDevelop can provide intellisense hints as you develop for the possible parameters, values and their meaning without having to look up the documentation every time.

Finally, for the sake of interoperability with the native platform, we exposed many types from the Java.* namespaces (31 so far) that you might need if you are interoperating with third party libraries that might require an instance of one of those Java.* types (for example, a crypto stack might want you to provide a Javax.Crypto.Cipher instance. We got you covered.

Core Differences

Mono for Android has a few differences from MonoTouch and Windows Phone 7 when it comes to the runtime. Android supports JIT compilation while iOS blocks it at the kernel level and Windows Phone 7 has limitations.

This means that developers using Mono on Android have complete access to System.Reflection.Emit. This in turn means that generics-heavy code like F# work on Android as do dynamic languages powered by the Dynamic Language Runtime like IronPython, IronRuby and IronJS.

And of course, you can also use our own C# Compiler as a Service

Now, although those languages can run on Mono for Android, we do not currently have templates for them. The Ruby and Python support suffer due to Android limitations. The Dalvik virtual needs to know in advance which classes you customize, and since it is not really possible to know this with a dynamic language, the use of Iron* languages is limited in that they cant subclass Android classes. But they can still call into Android APIs and subclass as much .NET class libraries as they want.

Native User Interfaces

MonoTouch and MonoDroid share a common runtime, a common set of class libraries, but each provides different user interface and device specific APIs.

For example, this code takes advantage of iOS's UINavigationController and animates the transition to a new state in response to a user action:

void OnSettingsTapped () { var settings = new SettingsViewController (); PushViewController (settings, true); }

This is an equivalent version for Mono for Android:

void OnSettingsTapped () { var intent = new Intent (); intent.SetClass (this, typeof (SettingsActivity)); StartActivity (intent); }

We chose to not follow the Java write-once-run-anywhere approach for user interfaces and instead expose every single bit of native functionality to C# developers.

We felt that this was necessary since the iOS and Android programming models are so different. We also wanted to make sure that everything that is possible to do with the native APIs on each OS continues to be possible while using Mono.

For instance, if you want to use CoreAnimation to drive your user interactions, you should be able to leverage every single bit of it, without being forced into a common denominator with Android where nothing similar to this is available.

Craig Dunn, one of the authors of the MonoTouch Programming Book, has written a nice Mosetta Stone document that compares side-by-side some of the key UI differences across platforms.

He also has written the Restaurant Guide Sample which sports a unique user interface for Android, iOS and Windows Phone 7: