Touch input basics in Unity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Detecting a single touch phase

What will be the output of this Unity C# script snippet when the user touches the screen and holds their finger still?

Unity

void Update() {
    if (Input.touchCount > 0) {
        Touch touch = Input.GetTouch(0);
        if (touch.phase == TouchPhase.Stationary) {
            Debug.Log("Finger is still on screen");
        }
    }
}

A No output, because touch.phase will never be Stationary

B Prints "Finger is still on screen" only when the finger is lifted

C Prints "Finger is still on screen" only once when the finger touches the screen

D Prints "Finger is still on screen" continuously while the finger is held still

💡 Hint

Think about what TouchPhase.Stationary means in Unity's touch system.

TouchPhase.Stationary means the finger is touching the screen but not moving. The code checks for this phase every frame, so it prints the message continuously while the finger is held still.

❓ Predict Output

intermediate

Counting touches on screen

What will be the value of the variable 'touchCount' after this code runs if the user has two fingers touching the screen?

Unity

int touchCount = Input.touchCount;

A 2

B 1

C 0

D Depends on the device

💡 Hint

Input.touchCount returns the number of fingers currently touching the screen.

Input.touchCount returns the number of active touches. If two fingers are on the screen, it returns 2.

🔧 Debug

advanced

Why does this touch position code cause an error?

This code tries to print the position of the first touch. Why does it cause an error when no fingers are touching the screen?

Unity

void Update() {
    Vector2 pos = Input.GetTouch(0).position;
    Debug.Log(pos);
}

A The code runs fine even with no touches

B Input.GetTouch(0) throws an exception if there are no touches

C Input.touchCount is zero so position is Vector2.zero

D Input.GetTouch(0) returns null causing a NullReferenceException

💡 Hint

Think about what happens if you ask for a touch index that does not exist.

Input.GetTouch(0) throws an ArgumentOutOfRangeException if there are no touches because index 0 is invalid.

🧠 Conceptual

advanced

Understanding TouchPhase.Moved behavior

Which statement best describes when TouchPhase.Moved is detected in Unity touch input?

A When the finger moves on the screen between frames

B When the finger is placed on the screen

C When the finger is lifted from the screen

D When the finger is held still on the screen

💡 Hint

Think about what 'Moved' means in the context of touch input.

TouchPhase.Moved means the finger is touching the screen and has changed position since the last frame.

❓ Predict Output

expert

Output of multi-touch gesture detection code

What will be printed by this Unity C# code if the user touches the screen with two fingers and moves both fingers?

Unity

void Update() {
    if (Input.touchCount == 2) {
        Touch touch0 = Input.GetTouch(0);
        Touch touch1 = Input.GetTouch(1);
        if (touch0.phase == TouchPhase.Moved && touch1.phase == TouchPhase.Moved) {
            Debug.Log("Two finger move detected");
        } else {
            Debug.Log("Not both fingers moved");
        }
    }
}

A "Not both fingers moved" if both fingers moved

B "Two finger move detected" even if only one finger moved

C "Two finger move detected" if both fingers moved this frame

D No output because Input.touchCount is never exactly 2

💡 Hint

Check the condition that requires both fingers to have moved.

The code prints "Two finger move detected" only if both fingers have the Moved phase in the same frame.