?. is a feature from C# 6, and as well as the => operator (when used for expression-bodied members), is available in Visual Studio 2015 only.
Read about them here null-conditional operators and here => operator
C# < 6 syntax:
protected virtual void OnConnectivityChanged(ConnectivityChangedEventArgs e)
{
if (ConnectivityChanged != null)
ConnectivityChanged.Invoke(this, e);
}
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