How to Fix the ‘GameObject.GetComponent()’ Error in Unity Using the Observer Pattern

Unity is a powerful game engine that uses C# for scripting, and while working with design patterns like Observer, it’s common to run into syntax or type-related issues especially when dealing with Unity components dynamically.

In this post, I’ll walk you through:

• My original Observer Pattern implementation
• What caused the GameObject.GetComponent() error
• How I fixed it
• And how I added more features to practice and improve the pattern

My Original Observer Pattern Code in Unity

Here’s the original Observer implementation I was working on. The idea is to make a Box GameObject react when it receives a notification (like jumping when a trigger happens).

using UnityEngine;
using System.Collections;

namespace ObserverPattern
{
    // Wants to know when another object does something interesting 
    public abstract class Observer 
    {
        public abstract void OnNotify();
    }

    public class Box : Observer
    {
        // The box GameObject which will do something
        GameObject boxObj;

        // What will happen when this box gets an event
        BoxEvents boxEvent;

        public Box(GameObject boxObj, BoxEvents boxEvent)
        {
            this.boxObj = boxObj;
            this.boxEvent = boxEvent;
        }

        // What the box will do if the event fits it
        public override void OnNotify()
        {
            Jump(boxEvent.GetJumpForce());
        }

        // The box will always jump in this case
        void Jump(float jumpForce)
        {
            // If the box is close to the ground
            if (boxObj.transform.position.y < 0.55f)
            {
                boxObj.GetComponent().AddForce(Vector3.up * jumpForce);
            }
        }
    }
}

The Error I Got

When I tried to run this code, Unity threw the following compile error:

error CS0411: The type arguments for method 'GameObject.GetComponent()' cannot be inferred from the usage. Try specifying the type arguments explicitly.

The problematic line was:

boxObj.GetComponent().AddForce(Vector3.up * jumpForce);

Why This Happen

GetComponent() is a generic method. That means Unity expects us to explicitly tell it what component we want, like:

boxObj.GetComponent<Rigidbody>()

Since I didn’t specify a type, Unity didn’t know which component I was trying to access and the compiler couldn’t infer it either. Hence the error.

The Simple Fix

Here’s how I corrected that line:

boxObj.GetComponent<Rigidbody>().AddForce(Vector3.up * jumpForce);

This explicitly tells Unity to get the Rigidbody component before calling AddForce().

My Improve and Expanded Version

After fixing the error, I decided to make my Observer Pattern more robust. I added:

• Component caching to avoid repeated GetComponent() calls
• A second behavior: changing color on notify
• A structure for checking different event types

Here’s the enhanced version of the Box class:

using UnityEngine;

namespace ObserverPattern
{
    public abstract class Observer
    {
        public abstract void OnNotify();
    }

    public class Box : Observer
    {
        GameObject boxObj;
        BoxEvents boxEvent;
        Rigidbody rb;

        public Box(GameObject boxObj, BoxEvents boxEvent)
        {
            this.boxObj = boxObj;
            this.boxEvent = boxEvent;

            // Cache the Rigidbody component
            rb = boxObj.GetComponent<Rigidbody>();
            if (rb == null)
            {
                Debug.LogError("Rigidbody not found on Box GameObject!");
            }
        }

        public override void OnNotify()
        {
            if (boxEvent.ShouldJump())
                Jump(boxEvent.GetJumpForce());

            if (boxEvent.ShouldFlash())
                FlashColor(boxEvent.GetFlashColor());
        }

        void Jump(float jumpForce)
        {
            if (boxObj.transform.position.y < 0.55f)
            {
                rb.AddForce(Vector3.up * jumpForce, ForceMode.Impulse);
                // You could add sound or animation trigger here
            }
        }

        void FlashColor(Color color)
        {
            Renderer rend = boxObj.GetComponent<Renderer>();
            if (rend != null)
            {
                rend.material.color = color;
                // Optionally: add coroutine to revert color after a short delay
            }
        }
    }
}

Practice Ideas to Build On

If you want to take this further, here are some practice features you could add:

• Multiple Observers: Make several boxes listen to the same event source.
• BoxEventType Enum: Handle multiple behaviors like Jump, Flash, Spin, Shrink, etc.
• Dynamic Subscription: Let boxes register/unregister themselves from the subject during runtime.
• UI Feedback: Show messages or logs in the UI when events are received.
• Object Pooling: Reuse observers and GameObjects instead of instantiating/destroying repeatedly.

Final Thoughts

The Observer Pattern is a powerful tool when building scalable and decoupled game systems in Unity. While implementing it, small issues like generic method usage (GetComponent<T>()) can trip you up but they’re easy to fix once you understand the syntax. After fixing my error, I expanded my project to include more interactive behaviors and optimizations, which made my code cleaner and more game-ready.