OnCollisionEnter2D and OnTriggerEnter2D in Unity - Mini Project: Build & Apply

Detecting Collisions and Triggers in Unity 2D

📖 Scenario: You are making a simple 2D game in Unity where a player can bump into walls and collect coins. You want to detect when the player hits a wall and when the player collects a coin.

🎯 Goal: Build a Unity C# script that uses OnCollisionEnter2D to detect hitting walls and OnTriggerEnter2D to detect collecting coins.

📋 What You'll Learn

Create a C# script with a OnCollisionEnter2D method that detects collisions with walls

Create a OnTriggerEnter2D method that detects triggers with coins

Use CompareTag to check if the collided object is a wall or a coin

Print messages to the console when collisions or triggers happen

💡 Why This Matters

🌍 Real World

Collision and trigger detection is essential in games to respond to player interactions with the environment and objects.

💼 Career

Game developers use these Unity methods daily to create interactive and responsive gameplay experiences.

1

Create the PlayerCollision script with empty methods

Create a C# script called PlayerCollision with empty methods OnCollisionEnter2D and OnTriggerEnter2D that take a parameter Collision2D collision and Collider2D other respectively.

Unity

// Create the PlayerCollision class with empty OnCollisionEnter2D and OnTriggerEnter2D methods
// Your code here

Need a hint?

Start by writing a public class named PlayerCollision. Inside it, add two methods: OnCollisionEnter2D with a Collision2D parameter and OnTriggerEnter2D with a Collider2D parameter. Leave the methods empty for now.

2

Add tag checks for walls and coins

Inside OnCollisionEnter2D, add an if statement that checks if collision.gameObject.CompareTag("Wall"). Inside OnTriggerEnter2D, add an if statement that checks if other.gameObject.CompareTag("Coin").

Unity

using UnityEngine;

public class PlayerCollision : MonoBehaviour
{
    void OnCollisionEnter2D(Collision2D collision)
    {
        // Add if statement to check if collision.gameObject.CompareTag("Wall")
        // Your code here
    }

    void OnTriggerEnter2D(Collider2D other)
    {
        // Add if statement to check if other.gameObject.CompareTag("Coin")
        // Your code here
    }
}

Need a hint?

Use CompareTag on the gameObject inside the collision or trigger parameter to check if it matches "Wall" or "Coin".

3

Add print statements inside the tag checks

Inside the if block for walls in OnCollisionEnter2D, add Debug.Log("Player hit a wall!"). Inside the if block for coins in OnTriggerEnter2D, add Debug.Log("Player collected a coin!").

Unity

using UnityEngine;

public class PlayerCollision : MonoBehaviour
{
    void OnCollisionEnter2D(Collision2D collision)
    {
        if (collision.gameObject.CompareTag("Wall"))
        {
            // Add Debug.Log("Player hit a wall!") here
            // Your code here
        }
    }

    void OnTriggerEnter2D(Collider2D other)
    {
        if (other.gameObject.CompareTag("Coin"))
        {
            // Add Debug.Log("Player collected a coin!") here
            // Your code here
        }
    }
}

Need a hint?

Use Debug.Log inside each if block to print the messages exactly as shown.

4

Test the script by printing messages on collision and trigger

Run the game and make sure when the player hits a wall, the console shows Player hit a wall! and when the player collects a coin, the console shows Player collected a coin!. Write Debug.Log statements as in the script and confirm the output.

Unity

// Run the game and check the console output
// Your code here

Need a hint?

Make sure your Unity console shows the exact messages when collisions and triggers happen.