Event Handling - Pro Unity Game Development with C# - page 99

Note Both the SendMessage and the BroadcastMessage functions are useful, but can cause
performance overhead when used extensively in frame-based functions, such as Update . For this reason,
use them judiciously and in a way that works well with your game. If you find their use to be generally too
costly for your game, then consider implementing an event system using C# interfaces. This subject will be
explored in brief in the final chapter.

 SendMessage. When you want to run a function of a specified name on all
components of a single GameObject, then you'll need the SendMessage function.
The declaration for this function is given as follows (also see the Unity online
documentation at http://docs.unity3d.com/Documentation/ ScriptReference/
Component.SendMessage.html) :
void SendMessage( string methodName, SendMessageOptions options );

 An example of its use is as follows:

MyGameObject.SendMessage("Myfunction", SendMessageOptions. DontRequireReceiver);

MethodName and Options. MethodName
refers to the function name to execute on all components of the specified
game object. The Options argument simply specifies what should happen if
a component is encountered that has no function with a matching name to
execute. Options can be either DontRequireReceiver or RequireReceiver.
DontRequireReceiver means that if a component is found with no matching
function to execute, then that component is simply ignored. RequireReceiver
means that if no function is found, an exception or error will be invoked
automatically by Unity and will be printed to the console.
 BroadcastMessage. Usually, SendMessage is all you need to invoke generic
behavior on a GameObject without knowing the implementation specifics
and interfaces of its components. But sometimes, you'll need more than this.
Specifically, you'll occasionally want to invoke functions and behavior on all
components across multiple GameObjects, and not just one object. If you
need multiple objects to simultaneously hide, show, die, move, explode,
change color, or do something else, then BroadcastMessage is your friend.
With BroadcastMessage , you simply send a message (invoke) a function
on the components of a single GameObject (as with SendMessage ), but
BroadcastMessage will proceed to cascade that invocation downward to all child
GameObjects automatically in the scene hierarchy (see Figure 3-7 ).

 This function accepts two arguments: