Keyboard input (GetKey, GetKeyDown) in Unity - Step-by-Step Execution

Concept Flow - Keyboard input (GetKey, GetKeyDown)

Start Frame

↓

Check GetKeyDown

↓

Trigger GetKeyDown Action

↓

Check GetKey

↓

Trigger GetKey Action

↓

End Frame

↩Back to Start Frame

Each frame, Unity checks if a key was just pressed (GetKeyDown) or is being held (GetKey), then triggers actions accordingly.

Execution Sample

Unity

void Update() {
  if (Input.GetKeyDown(KeyCode.Space)) {
    Debug.Log("Jump!");
  }
  if (Input.GetKey(KeyCode.Space)) {
    Debug.Log("Holding space");
  }
}

This code logs "Jump!" once when space is first pressed, and "Holding space" every frame while space is held.

Execution Table

Frame	Space Key State	Input.GetKeyDown(Space)	Input.GetKey(Space)	Action Taken	Output
1	Not pressed	False	False	None
2	Pressed this frame	True	True	GetKeyDown and GetKey triggered	Jump! Holding space
3	Held down	False	True	GetKey triggered	Holding space
4	Held down	False	True	GetKey triggered	Holding space
5	Released	False	False	None

💡 Space key released at frame 5, so no input detected.

Variable Tracker

Variable	Start	After Frame 1	After Frame 2	After Frame 3	After Frame 4	After Frame 5
Space Key State	Not pressed	Not pressed	Pressed this frame	Held down	Held down	Released
Input.GetKeyDown(Space)	False	False	True	False	False	False
Input.GetKey(Space)	False	False	True	True	True	False

Key Moments - 2 Insights

Why does GetKeyDown only trigger once even if the key is held?

GetKeyDown returns true only on the exact frame the key is first pressed, as shown in frame 2 of the execution_table. Subsequent frames with the key held down return false for GetKeyDown.

Why does GetKey return true on multiple frames?

GetKey returns true every frame the key is held down, as seen in frames 2, 3, and 4 in the execution_table, allowing continuous detection while holding.

Visual Quiz - 3 Questions

Look at the execution_table, what is Input.GetKeyDown(Space) at frame 3?

A True

B Null

C False

D Depends on previous frame

💡 Hint

Check the 'Input.GetKeyDown(Space)' column at frame 3 in the execution_table.

At which frame does the action 'Jump!' get logged?

A Frame 2

B Frame 1

C Frame 3

D Frame 5

💡 Hint

Look at the 'Action Taken' and 'Output' columns in the execution_table.

If the space key is held for 4 frames, how many times does 'Holding space' get logged?

A 1

B 4

C 3

D 2

💡 Hint

Check the 'Output' column for frames where Input.GetKey(Space) is true.

Concept Snapshot

Unity keyboard input:
- GetKeyDown detects key pressed this frame (once)
- GetKey detects key held down (every frame)
- Use in Update() for frame-based input
- GetKeyDown triggers action once per press
- GetKey triggers action continuously while held

Full Transcript

In Unity, keyboard input is checked every frame inside the Update() method. The function Input.GetKeyDown returns true only on the exact frame when a key is first pressed. This triggers actions that should happen once, like jumping. Input.GetKey returns true every frame while the key is held down, useful for continuous actions like running or charging. The execution table shows how these functions behave over several frames when the space key is pressed, held, and released. Beginners often confuse GetKeyDown with GetKey because GetKeyDown triggers only once per press, while GetKey triggers repeatedly while holding. Understanding this difference helps control game actions precisely.