Toast.cs

using UnityEngine;

public class Toast : MonoBehaviour {
    // Singleton
    static Toast instance;

    public static Toast GetInstance()
    {
        if (instance == null) {
            instance = FindObjectOfType<Toast>();

            if (instance == null) {
                GameObject GoToast = new GameObject("Toast");
                instance = GoToast.AddComponent<Toast>();
            }
        }

        return instance;
    }


    AndroidJavaObject curActivity = null;

    // Awake
    void Awake()
    {
        if (Application.platform == RuntimePlatform.Android) {
            AndroidJavaClass unityPlayer = new AndroidJavaClass("com.unity3d.player.UnityPlayer");
            curActivity = unityPlayer.GetStatic<AndroidJavaObject>("currentActivity");
        }
    }

    // Main Function
    public void DrawToast(string str)
    {
        if (str.Length == 0) {
            Debug.Log("null input");
        }
        else {
#if UNITY_EDITOR
            Debug.Log("Draw Toast : " + str);
#endif
            // Toast on Android
            if (Application.platform == RuntimePlatform.Android) {
                curActivity.Call("runOnUiThread", new AndroidJavaRunnable(() =>
                {
                    AndroidJavaObject toast = new AndroidJavaObject("android.widget.Toast", curActivity);
                    toast.CallStatic<AndroidJavaObject>("makeText", curActivity, str, 0).Call("show");
                }));
            }
        }
    }
}