around this issue There is no way avoid setting a value - if no value is specified it will default to default(T). But, with the latest XF version (> 18.104.22.1682) there is a Default property available that you can use to specify the fallback value.
<OnPlatform x:TypeArguments="x:Double" Default="25"> <!-- specify default value here -->
<Setter Property="Font" Value="30" />
I wish this helpful for you It looks like Write device platform specific code in Xamarin.Forms answers the question - which is not so much a Xamarin Forms question as a Visual Studio shared project question and can be solved by creating an interface/abstract class and then implementing that for each platform and injecting the implementation.
hop of those help? You only have one activity. Main you find it in your Droid app. If you need something specifically up in the activity code it there and initiate it from withen your Xamarin forms Page with an event. Pages don't really correlate to Activities at least not in the way your thinking. Xamarin Forms is Cross Platform by design thus if you couldn't do it on IOS, WP and Droid you cant do it inside Forms. Since obviously theres no Activities on the other 2 platforms Forms has no concept of an activity withen the PCL.
Can I use platform specific UI in a Xamarin.Forms solution?