public static BeepWirelessSpeaker()
{
WirelessSpeaker w = new WirelessSpeaker();
IBeepSpeakers wirelessSpeakerBeeper =
new IBeepSpeakers(w, s => ((WiredSpeaker)s).IsTransmitterOn = true);
wirelessSpeakerBeeper.BeepTheSpeaker();
}
public static BeepWirelessSpeaker_Version1()
{
// This is a valid assignment.
Speaker s = new WirelessSpeaker();
IBeepSpeakers wirelessSpeakerBeeper = new IBeepSpeakers(s);
// This call will fail!
// In WirelessSpeaker, we _OVERRODE_ the Beep method to check
// that TransmitterIsOn is true. But, IBeepSpeakers doesn't
// know anything _specifically_ about WirelessSpeaker speakers,
// so it can't set this property!
// Therefore, an InvalidOperationException will be thrown.
wirelessSpeakerBeeper.BeepTheSpeaker();
}
public static BeepWirelessSpeaker_Version2()
{
Speaker s = new WirelessSpeaker();
// I'm using a cast, to show here that IBeepSpeakers is really
// operating on a Speaker object. But, this is one way we can
// make IBeepSpeakers work, even though it thinks it's dealing
// only with Speaker objects.
//
// Since we set TransmitterIsOn to true, the overridden
// Beep method will now execute correctly.
//
// But, it should be clear that IBeepSpeakers cannot act on both
// Speakers and WirelessSpeakers in _exactly_ the same way and
// have confidence that an exception will not be thrown.
((WirelessSpeaker)s).TransmitterIsOn = true;
IBeepSpeakers wirelessSpeakerBeeper = new IBeepSpeaker(s);
// Beep the speaker. This will work because TransmitterIsOn is true.
wirelessSpeakerBeeper.BeepTheSpeaker();
}
