COIT20271 — Mobile Game Development

Week 10

Knowledge Revision

Review these concepts before attempting the Knowledge Check quiz.

MonoBehaviour Lifecycle

Awake()

Called when the script

instance is loaded,

even if disabled

▶

OnEnable()

Called when the

object becomes active

▶

Start()

Called once before

the first Update,

only if enabled

▶

FixedUpdate()

Fixed interval (0.02s)

Use for physics

& Rigidbody forces

▶

Update()

Every frame

Use for input,

non-physics logic

▶

LateUpdate()

After all Update

calls. Use for

camera follow

Key Points to Memorise�

• Awake() runs even if the script component is disabled. Start() waits until enabled.�

• FixedUpdate() is for Rigidbody/physics work. Update() is for everything else.�

• Applying forces in Update() causes jittery physics — always use FixedUpdate().�

• LateUpdate() runs after all Update() calls — ideal for camera follow scripts.

GetComponent & References

Getting References

// Cache in Start or Awake

Rigidbody rb;

​

void Awake() {

rb = GetComponent<Rigidbody>();

}

Returns null if the component is not attached → NullReferenceException if you use it.

[SerializeField] vs public

Common Bug: Unassigned Inspector References�

A public or [SerializeField] field that you forget to drag-assign in the Inspector defaults to null.�

Accessing any property on it (e.g., player.transform) throws NullReferenceException at runtime.

Collisions vs Triggers

Physical Collision

Is Trigger: OFF (unchecked)�

Objects physically bounce/push each other.�

�Callback:�

OnCollisionEnter(Collision col)

Trigger (Pass-Through)

Is Trigger: ON (checked)�

Objects pass through — detection zone only.�

�Callback:�

OnTriggerEnter(Collider other)

Both require: Both objects must have Colliders. At least one must have a Rigidbody.

Destroy(other) removes the Collider only. Use Destroy(other.gameObject) to remove the whole object.

Destroy & Instantiate

Destroy()

Destroy(gameObject); // Immediate

Destroy(gameObject, 3f); // After 3 seconds

Destroy(other); // Component only!

Destroy(other.gameObject); // Whole object

• The delay is in seconds, not frames.�

• Object stays active during the delay.�

• Destroying a Component ≠ destroying the GameObject.

Instantiate()

GameObject clone =

Instantiate(prefab,

position,

rotation);

• Returns a reference to the new clone.�

• The prefab field must be assigned in the Inspector.�

• Quaternion.identity = no rotation.

Coroutines — Spawning with Delays

IEnumerator SpawnLoop() {

while (true) {

Instantiate(prefab, pos, Quaternion.identity);

yield return new WaitForSeconds(2f); // Pauses THIS coroutine only

}

}

void Start() { StartCoroutine(SpawnLoop()); }

Input Handling

Input.GetAxis()

Returns a float from -1 to 1 with smoothing.��

"Horizontal" → A/Left = -1, D/Right = +1�

"Vertical" → S/Down = -1, W/Up = +1��

GetAxisRaw() returns -1, 0, or 1 with no smoothing.

float h = Input.GetAxis("Horizontal");

float v = Input.GetAxis("Vertical");

Vector3 move = new Vector3(h, 0, v);

rb.velocity = move * speed;

XZ plane movement — Y stays at 0.

Core Unity Concepts

Prefab

A saved GameObject template stored as an asset. Instantiate clones at runtime. Changes to the Prefab propagate to all instances.

Canvas

Required root parent for all UI elements (Text, Button, Image). Unity also needs an EventSystem for interactive elements.

Time.deltaTime

Seconds since last frame. Multiply speed values by this to get frame-rate independent movement (units per second, not per frame).

CompareTag()

Safer than tag == "string". Throws an exception if the tag doesn't exist in the Tag Manager — catches typos early.

Methods You Must Know