Incompatible types error: Manipulating return value of another class's method

Question

I need to yield a JsonObject in a class MainActivity from a method doInBackground() in a class Post.

I instantiated the class Post, called the method in it which is being passed parameters into, and tried to assign it to a variable of type JSONObject.

This is the class Post:

class Post extends AsyncTask<String, Void, JSONObject> {

    @Override
    protected JSONObject doInBackground(String... args) {
        JSONObject jsonObject = null;
        try {
            //Connect to the website
            Connection.Response response =
                    Jsoup.connect(args[0])
                            .method(Connection.Method.POST)
                            .data("text", args[1])
                            .data("language", args[2])
                            .ignoreContentType(true)
                            .execute();
            Document document = response.parse();
            jsonObject = new JSONObject(document.text());
        } catch (IOException e) {
            e.printStackTrace();
        } catch (JSONException err) {
            Log.d("Error", err.toString());
        }
        return jsonObject;
    }
}

And this is how I tried to retrieve the object in the class MainActivity:

Post post = new Post();
JSONObject object = post.execute(stringurl, text, "en");

The Java error I get is incompatible types. Required is org.json.JSONObject and found is android.os.AsyncTask <java.lang.String, java.lang.Void, org.json.JSONObject>.

I should be able to capture the JSONObject... how?

Answer 1

You can declare a method in MainActivity which can be called from the AsyncTask once it has fetched the JSONObject:

private onObtainJSONObject(JSONObject jsonObject){
    if(jsonObject != null){
        // do something with the JSONObject
    } else{
        // something went wrong - maybe show an error message?
    }
}

And you need to override onPostExecute() in the AsyncTask:

public void onPostExecute(JSONObject jsonObject){
    // Note: this will be executed on the main thread
    MainActivity.this.onObtainJSONObject(jsonObject);
}

If the AsyncTask is not an inner class of your Activity, you can use a callback (a simple interface) as follows

public interface PostCallback{
    void onSuccess(JSONObject data);
    void onError(Exception exception);
}

Then you let the AsyncTask have a field of type PostCallback and a setter setCallback(PostCallback).

In MainActivity:

Post post = new Post();
post.setPostCallback(new PostCallback(){

    @Override
    onSuccess((JSONObject data){
        onObtainJSONObject(data);
    }

    @Override
    onError(Exception exception){
        // exception handling ...
    }
});
JSONObject object = post.execute(stringurl, text, "en");

In Post:

private PostCallback callback;
private Exception exception;

public setPostCallback(PostCallback callback){
    this.callback = callback;
}

@Override
protected JSONObject doInBackground(String... args){
     // keep everything as before but when an Exception occurs,
     // assign it to *exception* in the catch block
} 

@Override
public void onPostExecute(JSONObject jsonObject){
    // Note: this will be executed on the main thread
    if(exception == null){
        callback.onSuccess(jsonObject);
    } else {
        callback.onError(exception);
    }
}