How can I pass an object to my AsyncTask?

Question

I have an object Car that has this constructor:

public Car(int idCar, String name)
{
    this.idCar = idCar;
    this.name = name;
}

Here I don't have any problem so I created one object Car named newCar, like this:

Car newCar = new Car(1,"StrongCar");

The problem that I have it's that I want to pass this newCar to my AsyncTask, named modifyCar as a parameter, but I don't know how to do this.

I have searched in SO and I found this question: AsyncTask passing custom objects but it doesn't solved my problem because in the solution that it is given they only pass an String to the AsyncTask and not the entirely object.

What I want it's to pass the entirely object as a parameter to the AsyncTask.

According to the solution that it is given in the question that I put above, I tried to do this to pass the object to the AsyncTask.

new modifyCar(newCar).execute();

So I declared the AsyncTask like this:

class modifyCar extends AsyncTask<Car, Integer, ArrayList<Evento>> {
 protected void onPreExecute()
 {
 }

 protected ArrayList<Evento> doInBackground(Car... newCarAsync) 
 {
     //The rest of the code using newCarAsync
 }

 protected void onProgressUpdate()
 {
 }

 protected void onPostExecute()
 {
 }
}

But I don't know if it is correct or not. If not, what I should do for that purpose?

Thanks in advance!

SaNtoRiaN · Accepted Answer · 2015-08-08T10:30:36.357

8

The solution that you read is right, you just did it wrong. You needed to create a constructor for your AsyncTask class easily and pass the object to it

class modifyCar extends AsyncTask<Void, Integer, ArrayList<Evento>> {
    private Car newCar;

    // a constructor so that you can pass the object and use
    modifyCar(Car newCar){
        this.newCar = newCar;
    }

    protected void onPreExecute()
    {
    }

    protected ArrayList<Evento> doInBackground(Void... parms) 
    {
        //The rest of the code using newCarAsync
    }

    protected void onProgressUpdate()
    {
    }

    protected void onPostExecute()
    {
    }
}

and to execute this class

// pass the object that you created
new modifyCar(newCar).execute();

edited Aug 08 '15 at 10:30

answered Aug 06 '15 at 18:23

SaNtoRiaN

2,212
2
15
25

But, in the `doInBackground()` method, how can I use the object `Car` in it? Or `newCarAsync` it's the same as the object `newCar` that it's declared in the `AsyncTask`? – Francisco Romero Aug 07 '15 at 11:03
@Error404 The object that you created is now passed to the class, inside the class or `doInBackground()` it's `newCar` – SaNtoRiaN Aug 08 '15 at 08:14
Then, what it's the purpose of `newCarAsync` variable in the `doInBackground()` method? – Francisco Romero Aug 08 '15 at 10:03
@Error404 It's useless, I just didn't want to change your class, I edited the class above – SaNtoRiaN Aug 08 '15 at 10:30
Thank you very much! You help me a lot! ;) – Francisco Romero Aug 08 '15 at 10:32

score 4 · Answer 2 · answered Aug 06 '15 at 17:18

4

It makes no difference if your object is an instance of String or a Car or a AbstractDeathRayController, the expected way to pass them to an AsyncTask is through the execute method:

new modifyCar().execute(car);

BTW, Java convention for class names is to use CamelCase, so it might be a good idea to rename your class to ModifyCar.

answered Aug 06 '15 at 17:18

Sebastian

1,076
9
24

Might be good to show how to access it in `doInBackground()` as well, as some have a hard time understanding varargs. – Daniel Nugent Aug 06 '15 at 19:20
As @DanielNugent said, I need to know how to access it in `doInBackground()` method because I don't really understand what you exactly want to say. – Francisco Romero Aug 07 '15 at 10:54

score 0 · Answer 3 · answered Aug 06 '15 at 17:19

You should pass the Car object on the execute method. You can read it in the documentation (http://developer.android.com/reference/android/os/AsyncTask.html):

An asynchronous task is defined by 3 generic types, called Params, Progress and Result, and 4 steps, called onPreExecute, doInBackground, onProgressUpdate and onPostExecute

Follow the documentation example:

private class DownloadFilesTask extends AsyncTask<URL, Integer, Long> {
     protected Long doInBackground(URL... urls) {
         int count = urls.length;
         long totalSize = 0;
         for (int i = 0; i < count; i++) {
             totalSize += Downloader.downloadFile(urls[i]);
             publishProgress((int) ((i / (float) count) * 100));
             // Escape early if cancel() is called
             if (isCancelled()) break;
         }
         return totalSize;
     }

     protected void onProgressUpdate(Integer... progress) {
         setProgressPercent(progress[0]);
     }

     protected void onPostExecute(Long result) {
         showDialog("Downloaded " + result + " bytes");
     }
 }

And call the async task with:

 new DownloadFilesTask().execute(url1, url2, url3);

How can I pass an object to my AsyncTask?

3 Answers3