How to Use Input in Unity: Basic Guide and Examples

In Unity, you use the Input class to detect user actions like keyboard presses, mouse clicks, or touch gestures. Call methods like Input.GetKey, Input.GetMouseButtonDown, or Input.touchCount inside the Update() method to respond to input events.

Syntax

The Input class provides several methods to check user input:

• Input.GetKey(KeyCode key): Returns true while the specified key is held down.
• Input.GetKeyDown(KeyCode key): Returns true during the frame the user starts pressing the key.
• Input.GetMouseButtonDown(int button): Returns true during the frame the mouse button is pressed (0 for left button).
• Input.touchCount: Returns the number of touches currently on the screen (for mobile).

These methods are usually called inside the Update() method to check input every frame.

csharp

void Update() {
    if (Input.GetKeyDown(KeyCode.Space)) {
        Debug.Log("Space key was pressed this frame.");
    }
    if (Input.GetMouseButtonDown(0)) {
        Debug.Log("Left mouse button clicked.");
    }
}

Example

This example shows how to move a game object left or right using arrow keys and detect mouse clicks to print messages in the console.

csharp

using UnityEngine;

public class SimpleInputExample : MonoBehaviour {
    public float speed = 5f;

    void Update() {
        float move = 0f;
        if (Input.GetKey(KeyCode.LeftArrow)) {
            move = -speed * Time.deltaTime;
        } else if (Input.GetKey(KeyCode.RightArrow)) {
            move = speed * Time.deltaTime;
        }
        transform.Translate(move, 0, 0);

        if (Input.GetMouseButtonDown(0)) {
            Debug.Log("Mouse left button clicked!");
        }
    }
}

Output

The game object moves left or right when arrow keys are held; clicking the left mouse button logs a message.

Common Pitfalls

Calling Input methods outside Update: Input checks should be inside Update() because input is checked every frame. Checking input in Start() or Awake() will not work as expected.

Using GetKeyDown vs GetKey: GetKeyDown triggers only once when the key is first pressed, while GetKey is true as long as the key is held. Use the right one for your need.

Not handling mobile input: Mouse input won't work on touch devices; use Input.touchCount and Input.GetTouch() for mobile.

csharp

void Update() {
    // Wrong: Checking input in Start will not detect key presses
}

void Start() {
    if (Input.GetKeyDown(KeyCode.Space)) {
        Debug.Log("Won't detect here");
    }
}

// Correct way:
void Update() {
    if (Input.GetKeyDown(KeyCode.Space)) {
        Debug.Log("Detected in Update");
    }
}

Quick Reference

Here is a quick summary of common Input methods:

Method	Description	Use Case
Input.GetKey(KeyCode key)	True while key is held down	Continuous movement or action
Input.GetKeyDown(KeyCode key)	True only on the frame key is pressed	Single action trigger
Input.GetMouseButtonDown(int button)	True on mouse button press frame	Detect mouse clicks
Input.touchCount	Number of current touches	Detect touches on mobile
Input.GetTouch(int index)	Get touch details by index	Handle touch gestures

Key Takeaways

Use Input methods inside Update() to check user input every frame.

Choose GetKeyDown for single press detection and GetKey for continuous press.

Use Input.touchCount and Input.GetTouch for mobile touch input.

Avoid checking input in Start() or Awake() as it won't detect user actions.

Test input on the target platform to ensure correct behavior.