BindableBase - 使用ViewModel实例的SetProperty不起作用

I am trying to set the property of the MainViewModel from LoginViewModel using an instance of the MainViewModel inside LoginViewModel . But the binding in XAML does not get notified ! I set the break point inside the MainViewModel and it shows the value is being set, but if its set through instance it does not work. Can anyone help? Below are the codes for both viewmodel. As you can see, in my loginviewmodel I set the public property using the instance of MainViewModel :I am trying to set the property of the MainView