I have an AsynkTask method on my MainActivity that it's the following:
class chargeCars extends AsyncTask<Void, Integer, ArrayList<Car>> {
protected void onPreExecute(){
}
protected ArrayList<Car> doInBackground(Void... params) {
ArrayList<Car> cars = new ArrayList<Car>();
cars.add(new Car(1,"Car1");
cars.add(new Car(2,"Car2");
cars.add(new Car(3,"Car3");
return cars;
}
protected void onProgressUpdate(){
}
protected void onPostExecute(ArrayList<Car> c){
}
}
where Car
it's an object that I have declared in another Class
and which constructor it's:
public Car(int idCar, String name)
{
this.idCar = idCar;
this.name = name;
}
and I know that return cars;
returns the ArrayList
named cars
to the method onPostExecute
but I tried to retrieve this ArrayList
from there and I couldn't because it always said to me that onPostExecute
method have to be Void
.
I have also another ArrayList
declared in my MainActivity
class:
ArrayList<Car> totalCars = new ArrayList<Car>();
so what I tried it's to clone cars
ArrayList into my totalCars
ArrayList in my onPostExecute
method but it gives me an error in which it says that:
'clone()' has protected access in 'java.lang.Object'
Here it's the code trying to clone my ArrayList:
protected void onPostExecute(ArrayList<Car> c)
{
for(Car cr: c)
{
totalCars.add(cr.clone());
}
}
So I also tried to add my values directly to my totalCars
ArrayList on my doInBackground
method:
totalCars.add(new Car(1,"Car1");
totalCars.add(new Car(2,"Car2");
totalCars.add(new Car(3,"Car3");
but when I execute my AsyncTask
method:
new chargeCars().execute();
the size of my totalCars
ArrayList it's equals to 0.
What should I do? I'm totally block and I searched in SO for an answer but I couldn't find anything that helps to me.
EDIT: My Car
Class it's:
public class Car {
private int idCar;
private String name;
public Car(){};
public Car(int idCar, String name)
{
this.idCar = idCar;
this.name = name;
}
public void setIdCar(int idCar)
{
this.idCar = idCar;
}
public int getIdCar()
{
return idCar;
}
public void setName(String name)
{
this.name = name;
}
public String getName()
{
return name;
}
}
EDIT 2: I put some logs to see what exactly does my program and I got strange results:
As Clairvoyant
said, I use both of his methods but any of them works. What could I saw? Well, I saw that in the onPostExecute
method the ArrayList contains values in both of the methods. Here there is no problem.
The problem it's that when I execute the AsyncTask in the method onCreate
of my MainActivity
class, my ArrayList totalCars
doesn't have any value inside, but in the method onPostExecute
of my AsyncTask it has all the values that I put inside the ArrayList.
What could be the problem?
EDIT 3: I also tried with:
public class MainActivity extends ActionBarActivity {
ArrayList<Car> cars = new ArrayList<Car>();
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
new chargeCars().execute();
Log.d("Size onCreate: ", "" + cars.size()); //It returns me a 0 -->Incorrect
}
class chargeCars extends AsyncTask<Void, Integer, Boolean> {
protected void onPreExecute(){
}
protected ArrayList<Car> doInBackground(Void... params) {
cars.add(new Car(1,"Car1");
cars.add(new Car(2,"Car2");
cars.add(new Car(3,"Car3");
Log.d("Size: ", "" + cars.size()); //It gives me the size equals to 3 -->Correct
return true;
}
protected void onProgressUpdate(){
}
protected void onPostExecute(boolean c){
}
}
}
But still doesn't work. I also tried to make a ProgressDialog
to be secure that my AsyncTask it's finished when I try to use my Log
in my onCreate
method but it also gives me an error (I have another question in SO about it but I don't know if it's a good practice in SO to make directly reference from another question so I don't post it here).
Am I doing something wrong? Why in my doInBackground
it gives me the correct size
of the ArrayList
and in my onCreate
method not?
Thanks in advance!
Because the execution is asynchronous and the
UI Thread
doesn't way the end of the execution of yourAsyncTask
to continue its execution flow. To get the results back, when yourAsyncTask
finishes its execution, without blocking theUI Thread
, you could use a delegate/lister.Let's declare an interface on the top of your Activity, and let't it implement this interface (you'll need to implement the methods). When
onCarsCompleted
is invoked you'll be able to print the correct size of yourArrayList
now we add a constructor to your
AsyncTask
, which takes as parameter an object of typeOnCarsListener
, and we keep a member reference to the object in the scope ofchargeCars
, andonPostExecute
we communicate back to theActivity
the results of your computation:And of course, you need to instantiate the AsyncTask like
new chargeCars(this).execute();