Unity 2017.3搭配Cardboard SDK 1.120：如何检测磁吸触发器？

Hey there! I’ve run into this exact problem with old Cardboard magnetic triggers and newer SDKs—you’re right, Google nixed official support in SDK 1.120, but we don’t need to revert to the buggy old 0.85 version. Below are two reliable ways to bring back that magnetic trigger functionality in your Unity 2017.3 project:

Virtually all old Cardboard magnetic triggers work by simulating a Volume Down key press when the magnet is pulled. We can directly listen for this in Unity and map it to your game’s trigger logic.

C# Implementation #

using UnityEngine;

public class CardboardMagnetHandler : MonoBehaviour
{
    // Event for other scripts to subscribe to
    public delegate void MagnetFired();
    public static event MagnetFired OnMagnetTriggered;

    void Update()
    {
        // Check if Volume Down was pressed this frame
        if (Input.GetKeyDown(KeyCode.VolumeDown))
        {
            FireMagnetAction();
        }
    }

    private void FireMagnetAction()
    {
        Debug.Log("Magnetic trigger activated!");
        // Trigger the event for any subscribed scripts
        OnMagnetTriggered?.Invoke();
    }
}

How to Use #

1. Attach this script to a persistent GameObject in your scene (like a GameManager that stays loaded)
2. In any script that needs to respond to the magnetic trigger, subscribe to the event:

void OnEnable()
{
    CardboardMagnetHandler.OnMagnetTriggered += HandleMagnetInput;
}

void OnDisable()
{
    CardboardMagnetHandler.OnMagnetTriggered -= HandleMagnetInput;
}

private void HandleMagnetInput()
{
    // Add your game logic here—like raycasting for object interaction, firing a weapon, etc.
}

Some early Cardboard models use a hall sensor instead of simulating a key press. If your device supports it, you can read directly from the hall sensor to detect when the magnet is moved.

C# Implementation (Simplified) #

using UnityEngine;

public class HallSensorMagnetDetector : MonoBehaviour
{
    public delegate void MagnetStateChanged(bool isMagnetNear);
    public static event MagnetStateChanged OnMagnetDetected;

    [SerializeField] private float magnetThreshold = 0.6f;
    private float lastMagneticStrength;

    void Update()
    {
        // Read raw magnetic field data from the device's compass
        Vector3 magneticData = Input.compass.rawVector;
        float currentStrength = magneticData.magnitude;

        // Check if the magnetic field changed enough to trigger an event
        if (Mathf.Abs(currentStrength - lastMagneticStrength) > magnetThreshold)
        {
            bool magnetIsNear = currentStrength > lastMagneticStrength;
            OnMagnetDetected?.Invoke(magnetIsNear);
            lastMagneticStrength = currentStrength;
        }
    }

    void Start()
    {
        // Enable the compass to access magnetic field data
        Input.compass.enabled = true;
    }
}

Notes #

• If your device doesn’t have a hall sensor, this will fall back to using the compass magnetic field data, which is less precise. For full hall sensor support, you’d need a small Android native plugin to listen directly to the sensor callbacks (but the above works for most cases).
• Adjust the magnetThreshold value based on your specific Cardboard model and device—test to find what works best.

If you’re dead-set on using SDK 0.85, those build errors are almost always from compatibility issues between Unity 2017.3 and the old SDK. Try these fixes:

• Set your Android Build Target to API Level 26 or lower (old SDKs don’t support newer API levels)
• Delete Unity’s Library folder and reimport the SDK to resolve cache conflicts
• Check for conflicting dependencies between the old SDK and Unity’s built-in Android libraries

That said, Solution 1 is the most reliable and low-fuss option—no SDK downgrades needed, and it works with almost all old Cardboard models.

内容的提问来源于stack exchange，提问作者Hung Lam Vu Ngo