How to return more than one value using an asyncTask in android?

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How to return more than one value using an asyncTask in android?

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#1 by (2 votes)

4

In short, my class that extends an AsyncTask, downloads a series of data of type byte, then I need to perform some calculations with that data, and finally return all these values to my MainActivity.

The code is summarized as follows:

class DataDownloaderTask extends AsyncTask<String, Void, byte[]> {

private String url;
private Context context;
private static byte[] data;

//--------------------CONSTRUCTOR--------------------------------//
public DataDownloaderTask(Context context) {
    this.data = null;
    this.context = context;
}

//--------------BACKGROUND---------------------------------------//
@Override
// Actual download method, run in the task thread
protected byte[] doInBackground(String... params) {
    // params comes from the execute() call: params[0] is the url.
    return downloadData(params[0]);
}

//--------------POST EXECUTE-------------------------------------//
@Override
// Once the image is downloaded
protected void onPostExecute(byte[] data) {
    if(data != null){
        Toast.makeText(this.context,"Operação concluida com sucesso!", Toast.LENGTH_SHORT).show();
    }else{
        pDialog.dismiss();
        Toast.makeText(this.context,"O ficheiro nao existe ou ocorreu um erro de conexão!", Toast.LENGTH_SHORT).show();
    }
}

The method that downloads the data:

static Bitmap downloadData(String url) {

   //Download the data from url...

   //Calculate other values...
   int value1 = 0;
   int value2 = 1;
   double value 3 = 0.1;

   //COMO RETORNAR OS DADOS: value1 value2 value 3 ...?

   return data;
}

In my MainActivity I have a method that does this:

DataDownloaderTask object = new DataDownloaderTask(MainActivity.this);
object.execute(string);

    try {
        mydata = object.get(); //mydata é to tipo byte[]
    } catch (Exception e) {
        return false;
    }

So, I would like to know how I can get other values of different types computed in this same AsyncTask in my MainActivity class, in addition to the "data" byte array. Thanks!

android return asynctask

asked by anonymous 22.06.2015 / 13:32

1 answer

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score 2 · Accepted Answer

A method only returns a data type, however, this type does not necessarily need to be a simple type such as int , String , boolean , etc.
So, when you want to return a dataset, a class is used.

Type a class that has the attributes you want to return:

public class MeusDados{
    private int mValue1;
    private int mValue2;
    private double mValue3;
    private byte[] mData;

    public MeusDados(int value1, int value2, double value3, byte[] data){
        mValue1 = value1;
        mValue2 = value2;
        mValue3 = value3;
        mData = data;
    }

    public int getValue1(){
        return mValue1;
    }

    public int getValue2(){
        return mValue2;
    }
    public double getValue3(){
        return mValue3;
    }
    public byte[] getData(){
        return mData;
    }
}

Declare AsyncTask so that the type that the doInBackground() method returns is this class:

class DataDownloaderTask extends AsyncTask<String, Void, MeusDados> {

    .....
    .....
}

The doInBackground() method is declared as follows:

@Override
// Actual download method, run in the task thread
protected MeusDados doInBackground(String... params) {
    // params comes from the execute() call: params[0] is the url.
    return downloadData(params[0]);
}

In the downLoadData() method, create an object of the type by passing the constructor byte[] and calculated data:

static MeusDados downloadData(String url) {

   //Download the data from url...
   byte[] data = //ler do url

   //Calculate other values...
   int value1 = 0;
   int value2 = 1;
   double value3 = 0.1;

   //Criar objecto MeusDados
   MeusDados dados = new MeusDados(value1, value2, value3, data);
   //Retornar o conjunto de dados
   return dados;
}

In the onPostExecute() fault method, you receive this dataset:

@Override
// Once the image is downloaded
protected void onPostExecute(MeusDados dados) {
    if(dados.getData != null){
        Toast.makeText(this.context,"Operação concluida com sucesso!", Toast.LENGTH_SHORT).show();
    }else{
        pDialog.dismiss();
        Toast.makeText(this.context,"O ficheiro nao existe ou ocorreu um erro de conexão!", Toast.LENGTH_SHORT).show();
    }
}