Calling Android/Java methods from Unity C# script using AndroidJavaObject is not working

Unity Engine
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1

Unity newbie here. I have integrated unityLib.aar as library in my Android project and everything is working fine. I am able to call Unity C# methods from my Android/Java code, but I am not able to call Java/Android method from my Unity code.

I have built a basic test project to implement this functionality without any success.

What I have implemented -

  1. A single scene which have a Unity UI button
  2. Unity UI button on click will call a method changeButtonColor() defined below
  3. In changeButtonColor method I am implementing below should call buttonClickedTest defined in Android activity: -
buttonUnity.onClick.AddListener(changeButtonColor);

void changeButtonColor(){

    AndroidJavaClass unityPlayerClass = new AndroidJavaClass("com.unity3d.player.UnityPlayer");

    AndroidJavaObject currentActivity = unityPlayerClass.GetStatic<AndroidJavaObject ("currentActivity");

    AndroidJavaObject callAndroidMethod = new AndroidJavaObject("com.example.unitytest.UnityPlayerActivity");

    callAndroidMethod.Call("buttonClickedTest");
}

  1. Last line is supposed to calling method buttonClickedTest defined in Android activity which is changing native android button’s color and text color.

  2. There’s only one activity in my Android project UnityActivityPlayer and method buttonClickedTest() is defined in it.

  3. Since it was not working, I changed method signature and called last line in following permutation (not together): -

callAndroidMethod.Call("buttonClickedTest", currentActivity);
callAndroidMethod.Call("buttonClickedTest", parameters);
  1. None of above is working. Definitely I am missing something. Please guide.[/code]
2

First find if your C# code above is running.

Then find out if anything in Android is complaining by looking in the log (see below).

You must find a way to get the information you need in order to reason about what the problem is.

Once you understand what the problem is, you may begin to reason about a solution to the problem.

What is often happening in these cases is one of the following:

  • the code you think is executing is not actually executing at all
  • the code is executing far EARLIER or LATER than you think
  • the code is executing far LESS OFTEN than you think
  • the code is executing far MORE OFTEN than you think
  • the code is executing on another GameObject than you think it is
  • you’re getting an error or warning and you haven’t noticed it in the console window

To help gain more insight into your problem, I recommend liberally sprinkling Debug.Log() statements through your code to display information in realtime.

Doing this should help you answer these types of questions:

  • is this code even running? which parts are running? how often does it run? what order does it run in?
  • what are the values of the variables involved? Are they initialized? Are the values reasonable?
  • are you meeting ALL the requirements to receive callbacks such as triggers / colliders (review the documentation)

Knowing this information will help you reason about the behavior you are seeing.

You can also supply a second argument to Debug.Log() and when you click the message, it will highlight the object in scene, such as Debug.Log("Problem!",this);

If your problem would benefit from in-scene or in-game visualization, Debug.DrawRay() or Debug.DrawLine() can help you visualize things like rays (used in raycasting) or distances.

You can also call Debug.Break() to pause the Editor when certain interesting pieces of code run, and then study the scene manually, looking for all the parts, where they are, what scripts are on them, etc.

You can also call GameObject.CreatePrimitive() to emplace debug-marker-ish objects in the scene at runtime.

You could also just display various important quantities in UI Text elements to watch them change as you play the game.

If you are running a mobile device you can also view the console output. Google for how on your particular mobile target, such as this answer or iOS: How To - Capturing Device Logs on iOS or this answer for Android: How To - Capturing Device Logs on Android

If you are working in VR, it might be useful to make your on onscreen log output, or integrate one from the asset store, so you can see what is happening as you operate your software.

Another useful approach is to temporarily strip out everything besides what is necessary to prove your issue. This can simplify and isolate compounding effects of other items in your scene or prefab.

Here’s an example of putting in a laser-focused Debug.Log() and how that can save you a TON of time wallowing around speculating what might be going wrong:

When in doubt, print it out!™

Note: the print() function is an alias for Debug.Log() provided by the MonoBehaviour class.

3

Appreciate your response. It will help me in debugging.

But problem here is I am not sure correct what is correct code for calling java method from unity script.

Can you guide if code to call java methods is incorrect and where?

4

I’ve never done it… the first place I would start is in the example code provided for the Unity Android integration stuff you found above (AndroidJavaClass and AndroidJavaObject).

5

Thanks

6

This line looks wrong. Here you try to create new instance of this class. If you’ve modified the activity, you already have activity instance in your code, call the method on that.