Power-Ups and Singletons - Pro Unity Game Development with C# - page 133

40 //Get PlayerController object and update cash
41 PlayerController PC = Other.gameObject.GetComponent<PlayerController>();
42
43 //If there is a PC attached to colliding object, then update cash
44 if(PC) PC.Cash += CashAmount;
45 }
46 //--------------------------------------------------------------
47 }
Note More information on Unity trigger events can be found at http://docs.unity3d.com/
Documentation/ScriptReference/MonoBehaviour.OnTriggerEnter.html and
http://docs.unity3d.com/Documentation/ScriptReference/MonoBehaviour.
OnTriggerExit.html .
 Lines 16-25. The Start event demonstrates an important and useful function
in Unity, namely GameObject.FindGameObjectWithTag . Using this function, the
purpose of Start is to search through all game objects in the scene , finding an
object with a tag of “ sounds ”, and then to retrieve a reference to its AudioSource
component, if it has one. This component will be used to play back any sounds
associated with this power-up when it's collected. The success of this function
depends on there actually being an object in the scene that has a tag of
“ sounds ” and an AudioSource component. Thus, if there isn't such an object,
be sure to add one. Thankfully, however, this power-up has been coded so
that if no such object is present, the power-up will simply not play a sound on
collection, as opposed to throwing an error or exception.
Note I recommend taking a look at the FindGameObjectWithTag function on the Unity online
documentation. It can be really useful for retrieving references to objects at runtime by object
tags (see http://docs.unity3d.com/Documentation/ScriptReference/GameObject.
FindGameObjectsWithTag.html ) .
 Lines 29-32. The OnTriggerEnter function is inherited from Component , and is
executed automatically by Unity as an event, whenever a collision is detected
with the trigger. Here is where we should code a response to collision events.
The function argument Other is a reference to the object that is colliding with us,
and it's an important parameter for validating a collision. The power-ups for this
game should be collected by the Player only, and not by wandering Enemies.
But since both the Player and the Enemies will have colliders, both of them will
be able to collide with, and possibly collect, the power-up—unless we validate
the Other object! This validation occurs in line 32, where we check to see if the
colliding object is marked with the "player" tag. If it's not, then the event is
ignored. Consequently, for the collision functionality to work here, the Player
object must be marked with the tag "player" .