Unity中AndroidJavaProxy方法参数为null的坑

AndroidJavaProxy是个好东西,可以让安卓原生代码直接调用Unity的代码，而不用通过SendMessage的方式。

今天在使用的过程中发现一个问题，Android调用Unity的方法时报错:

No such proxy method: xxxx(AndroidJavaObject)

经过各种尝试和Google以后发现了最终的原因：

首先贴出代码

Java代码IListener.java

package com.company.test;

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

Java代码: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代码: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场景中把Test.cs脚本挂到GameObject上打包在真机运行会报以下错误:

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

问题出现的是在UnityEngine.AndroidJavaProxy.Invoke的实现中

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)
        // 如果参数为null则将类型设置为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;
    }

当Java调用Unity方法传递过来的值为null时，AndroidJavaProxy会按照参数类型为AndroidJavaObject的方式去查找方法(见上面第8行代码)，自然就找不到。然后就报错了

解决方法也很简单，重写Invoke方法避免查找Method失败就可以了

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

再次打包程序运行就不会报错，能正常输出日志了.

   PS:上面的修复代码只是测试使用，正式项目中请自行补全错误处理，参数转换以及多方法的支持等代码