How to wait for async operation (any I/O) in Android java plugin side?

Question

For a unity game I need to use libs in android-plugin that will send websocket requests. I found out that I have no idea how make the c# code wait for the async operation in android plugin!

I provide a proof of concept case (with simple http get request) to ask my quesiton the simple way. Here are my code that didnt' work:

package com.example.plug2unity1;
import java.io.IOException;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;

public class Plug1Class {
  static OkHttpClient client = new OkHttpClient();
  static String doGetRequest(String url) throws IOException {
    Request request = new Request.Builder()
            .url(url)
            .build();

    Response response = client.newCall(request).execute();
    return response.body().string();
  }
  public static String GetPlug2Text() throws IOException {
    String res = "";
    try {
        res = doGetRequest("http://www.google.com");
    } catch (IOException e) {
        e.printStackTrace();
    }
    return res;
  }
}

Unity script will have to call the plugin:

void Start () {
    TextMesh txtm = GetComponent<TextMesh> ();
    var plugin = new AndroidJavaClass("com.example.plug2unity1.Plug1Class");
    txtm.text = plugin.CallStatic<string>("GetPlug1Text");
}

Edit: The question is "not" how to make http call, it is obvious that from c# I can do it, I would like to learn "how c# could wait an async operation result from plugin, being it an http call or an I/O operation, same way we do by "promises" in javascript.

Result:
My TextMesh does not change the text, while if I do a POC without any async in plugin side, it works. How could I get this to work?

Why are you making the web request from Java? Why not do it from Unity's C# side? — Programmer, Mar 03 '18 at 20:27
That's obvious! I wrote above that I simplified my question in this form. I would like to know exactly the answer to above question: if plugin is doing something async, how c# could wait the response please? — Ariam1, Mar 03 '18 at 20:31
Ok that makes sense. I was just making sure you are not struggling with making webreq calls in C#. — Programmer, Mar 03 '18 at 21:00
Thanks, any idea about this question is very welcome, I'm stucked now and surfing google is giving nothing, perhaps because I don't know what exactly to search! — Ariam1, Mar 03 '18 at 21:04

score 1 · Accepted Answer · answered Mar 03 '18 at 21:08

Use a callback to do this. Call the Java unction from C#. In the Java function, start new Thread to perform that task. When that task has finished, do a callback from Java to C# to let you know that the task has finished.

C# sample code:

void makeRequestOnJava() 
{
    TextMesh txtm = GetComponent<TextMesh> ();
    var plugin = new AndroidJavaClass("com.example.plug2unity1.Plug1Class");
    txtm.text = plugin.CallStatic<string>("GetPlug1Text");
}

//Will be called from C# when the request is done
void OnRequestFinished()
{

}

Then on the Java side when your task has finished, use UnityPlayer.UnitySendMessage to call the OnRequestFinished function on the C# side.

UnityPlayer.UnitySendMessage("GameObjectName", "OnRequestFinished", null);

You can see how to setup and use the UnityPlayer.UnitySendMessage function here.

How to wait for async operation (any I/O) in Android java plugin side?

1 Answers1