Unity中AndroidJavaProxy方法參數為null的坑

AndroidJavaProxy是個好東西,可以讓安卓原生代碼直接調用Unity的代碼，而不用通過SendMessage的方式。

今天在使用的過程中發現一個問題，Android調用Unity的方法時報錯:

No such proxy method: xxxx(AndroidJavaObject)

經過各種嘗試和Google以后發現了最終的原因：

首先貼出代碼

Java代碼IListener.java

package com.company.test;

public interface IListener {
    public void onComplete(String error);
}

Java代碼:Test.java

package com.company.test;

public class Test {
    
    private IListener listener;
    
    public void setListener(IListener listener) {
        this.listener = listener;
    }
    
    public void doTask() {
        listener.onComplete(null);
    }
    
    public static Test create() {
        return new Test();
    }
}

Unity代碼:Test.cs

using UnityEngine;

public class Test : MonoBehaviour
{
    private AndroidJavaObject nativeJavaObject;

    class Listener : AndroidJavaProxy
    {
        public Listener() : base("com.company.test.IListener")
        {
            
        }

        void onComplete(string error)
        {
            Debug.Log($"onComplete:{error}");
        }
    }
    // Start is called before the first frame update
    void Start()
    {
        AndroidJavaClass javaClass = new AndroidJavaClass("com.company.test.Test");
        nativeJavaObject = javaClass.CallStatic<AndroidJavaObject>("create");
        nativeJavaObject.Call("setListener", new Listener());
        nativeJavaObject.Call("doTask");
    }
}

　　Unity場景中把Test.cs腳本掛到GameObject上打包在真機運行會報以下錯誤:

No such proxy method: Test+Listener.onComplete(UnityEngine.AndroidJavaObject)

問題出現的是在UnityEngine.AndroidJavaProxy.Invoke的實現中

public virtual AndroidJavaObject Invoke(string methodName, object[] args)
    {
      Exception inner = (Exception) null;
      BindingFlags bindingAttr = BindingFlags.Instance | BindingFlags.Static | BindingFlags.Public | BindingFlags.NonPublic;
      System.Type[] types = new System.Type[args.Length];
      for (int index = 0; index < args.Length; ++index)
        // 如果參數為null則將類型設置為AndroidJavaObject
        types[index] = args[index] == null ? typeof (AndroidJavaObject) : args[index].GetType();
      try
      {
        MethodInfo method = this.GetType().GetMethod(methodName, bindingAttr, (Binder) null, types, (ParameterModifier[]) null);
        if (method != null)
          return _AndroidJNIHelper.Box(method.Invoke((object) this, args));
      }
      catch (TargetInvocationException ex)
      {
        inner = ex.InnerException;
      }
      catch (Exception ex)
      {
        inner = ex;
      }
      string[] strArray = new string[args.Length];
      for (int index = 0; index < types.Length; ++index)
        strArray[index] = types[index].ToString();
      if (inner != null)
        throw new TargetInvocationException(this.GetType().ToString() + "." + methodName + "(" + string.Join(",", strArray) + ")", inner);
      AndroidReflection.SetNativeExceptionOnProxy(this.GetRawProxy(), new Exception("No such proxy method: " + (object) this.GetType() + "." + methodName + "(" + string.Join(",", strArray) + ")"), true);
      return (AndroidJavaObject) null;
    }

當Java調用Unity方法傳遞過來的值為null時，AndroidJavaProxy會按照參數類型為AndroidJavaObject的方式去查找方法(見上面第8行代碼)，自然就找不到。然后就報錯了

解決方法也很簡單，重寫Invoke方法避免查找Method失敗就可以了

public override AndroidJavaObject Invoke(string methodName, object[] args)
        {
            if (methodName == "onComplete")
            {
                onComplete(args[0] as string);
                return null;
            }
            return base.Invoke(methodName, args);
        }

再次打包程序運行就不會報錯，能正常輸出日志了.

   PS:上面的修復代碼只是測試使用，正式項目中請自行補全錯誤處理，參數轉換以及多方法的支持等代碼