24

I have

public class MyApp : Application

In Java I would add a line to the manifest and pass it the namespace and name of my application:

<application android:icon="@drawable/icon" android:label="@string/app_name"
    android:name="com.devahead.extendingandroidapplication.MyApplication">

In Xamarin, there is the [Application] attribute but the documentation states that the Name member is not supported. So how do I get my subclass registered? Where to apply the attribute to?

If I add the attribute to my subclass, I get:

System.NotSupportedException: Unable to activate instance of type TestClient_Android.MyApplication from native handle 14d00019
Krumelur
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1 Answers1

59

Found it. The documentation is outdated. You will need a special c'tor with two parameters and you will have to add the [Application] attribute:

[Application]
public class MyApplication : Application
{
    public MyApplication(IntPtr handle, JniHandleOwnership ownerShip) : base(handle, ownerShip)
    {
    }
}

EDIT: In addition it seems one has to override OnCreate(). If you have only the constructor, it will not be called.

public override void OnCreate()
{
  // If OnCreate is overridden, the overridden c'tor will also be called.
  base.OnCreate();
}

EDIT November 2015: here's a link to the Xamarin documentation which explains why this behavior exists.

...Xamarin.Android hooks into this by adding a mono.MonoRuntimeProvider ContentProvider to AndroidManifest.xml during the build process. The mono.MonoRuntimeProvider.attachInfo() method is responsible for loading the Mono runtime into the process. Any attempts to use Mono prior to this point will fail. ( Note: This is why types which subclass Android.App.Application need to provide an (IntPtr, JniHandleOwnership) constructor, as the Application instance is created before Mono can be initialized.)

Krumelur
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  • Tis really hard to find the answer like this for mono/xamarin android – macio.Jun Dec 23 '14 at 20:09
  • The notation I found [here](http://stackoverflow.com/a/9963637/426227) or [here](https://manski.net/2012/04/creating-an-application-class-in-mono-for-android/) is slightly different (`javaReference` instead of `handle`). Does this make a difference? – testing May 25 '16 at 08:41
  • @testing how you name the parameters does not matter. The types have to match. – Krumelur May 26 '16 at 17:36
  • All was working fine until latest Xamarin update and everything stopped. Adding the additional OnCreate fixed our issue. Even though we had it overridden in base class we were inheriting from that so had to add to child too. Thanks for the info, was forcing us to stay on old version of Xamarin. – KrustyGString Aug 17 '16 at 16:09
  • So how would i apply a theme for the application using the [assembly: Application(Theme = "style here")] in the AssemblyInfo file since i won't be allowed to add that line there once i have a custome Application class? – Joseph Oct 17 '16 at 22:43
  • Please make this a new question. – Krumelur Oct 18 '16 at 05:00
  • How can i add Xamarin.Forms.Init() in Application OnCreate() Method – Lutaaya Huzaifah Idris Oct 30 '17 at 14:49