UI Components can't locate "onClick" callback methods

This is my XML code:

    <Button
    android:text="Button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@id/MyButton"
    android:id="@+id/button1"
    android:onClick="sayHellow" /> //RELEVANT PART

And this is my main activity:

[Activity(Label = "FFFF", MainLauncher = true, Icon = "@drawable/icon", Theme = "@style/Theme.AppCompat.Light")]
public class MainActivity : AppCompatActivity
{
    protected override void OnCreate(Bundle bundle)
    {
        base.OnCreate(bundle);

        // Set our view from the "main" layout resource
        SetContentView(Resource.Layout.Main);
    }
    public void sayHellow(View v) //CALLBACK FUNCTION
    {
        Snackbar.Make(v, "My text", Snackbar.LengthLong)
            .Show();
    }
}

Problem is I get a runtime error and the debug window complains that Buttoncould not find "sayHellow" function, but as you can see I declared everything according to the docs.