Xamarin.Form之Android错误 `Android.Runtime.IJavaObject` but does not inherit `Java.Lang.Object` 的解决方法

错误，如：error XA4212: Type `Abc.Droid.Services.WeChat` implements `Android.Runtime.IJavaObject` but does not inherit `Java.Lang.Object` or `Java.Lang.Throwable`. This is not supported.

解决方法：

把这个WeChat的类首先继承一下 Java.Lang.Object 

...
namespace Abc.Droid.Services
{
    public class WeChat : Java.Lang.Object, IWeChat, IWXAPIEventHandler
    {
...
    }
 }