Object[] cannot be cast to Void[] in AsyncTask

Question

I'm getting this error inside an extended asynctask, but i'm really sure that Object[] IS a Void[].

This is my custom AsyncTask:

public abstract class RepeatableAsyncTask<A, B, C> extends AsyncTask<A, B, C> {
private static final String TAG = "RepeatableAsyncTask";
public static final int DEFAULT_MAX_RETRY = 5;

private int mMaxRetries = DEFAULT_MAX_RETRY;
private Exception mException = null;

/**
 * Default constructor
 */
public RepeatableAsyncTask() {
    super();
}

/**
 * Constructs an AsyncTask that will repeate itself for max Retries
 * @param retries Max Retries.
 */
public RepeatableAsyncTask(int retries) {
    super();
    mMaxRetries = retries;
}

/**
 * Will be repeated for max retries while the result is null or an exception is thrown.
 * @param inputs Same as AsyncTask's
 * @return Same as AsyncTask's
 */
protected abstract C repeatInBackground(A...inputs);

@Override
protected final C doInBackground(A...inputs) {
    int tries = 0;
    C result = null;

    /* This is the main loop, repeatInBackground will be repeated until result will not be null */
    while(tries++ < mMaxRetries && result == null) {
        try {
            result = repeatInBackground(inputs);
        } catch (Exception exception) {
            /* You might want to log the exception everytime, do it here. */
            mException = exception;
        }
    }
    return result;
}

/**
 * Like onPostExecute but will return an eventual Exception
 * @param c Result same as AsyncTask
 * @param exception Exception thrown in the loop, even if the result is not null.
 */
protected abstract void onPostExecute(C c, Exception exception);

@Override
protected final void onPostExecute(C c) {
    super.onPostExecute(c);
    onPostExecute(c, mException);
}

And this is the SubClass that gives the problem:

public class ListPalinasAsynkTask extends RepeatableAsyncTask<Void, Void, List<Palina>>{
    private static final String TAG = "ListPalinasAsynkTask";
    private static final boolean D = SystemConstants.ACTIVE_DEBUG;

    private ApiRequest.ListPalinasCallback mCallback;

    public ListPalinasAsynkTask(ApiRequest.ListPalinasCallback callback) {
        if(D) Log.d(TAG, "Called: ListPalinasAsynkTask([callback])");
        mCallback = callback;
    }

    @Override
    protected List<Palina> repeatInBackground(Void... voids) {
        /* Here i send request to get palinas */
        return Api.getPalinasNearMe();
    }

    @Override
    protected void onPostExecute(List<Palina> palinas, Exception exception) {
        if(exception != null)
            Logging.e(TAG, "Received exception in Asynk Task", exception);
        if(palinas != null)
            mCallback.result(palinas);
        else
            mCallback.result(new ArrayList<Palina>());
    }
}

Finally, this is the error:

E/ListPalinasAsynkTask﹕ Received exception in Asynk Task
    java.lang.ClassCastException: java.lang.Object[] cannot be cast to java.lang.Void[]
            at ListPalinasAsynkTask.repeatInBackground(ListPalinasAsynkTask.java:19)
            at RepeatableAsyncTask.doInBackground(RepeatableAsyncTask.java:43)
            at android.os.AsyncTask$2.call(AsyncTask.java:288)

I can't explain this exception because i'm giving Void as a parameter! That should not be an Object. Do you have solutions?

Edit: ListPalinasAsyncTask.java:19 refers to:

public class ListPalinasAsynkTask extends RepeatableAsyncTask<Void, Void, List<Palina>> {

RepeatableAsyncTask.java:43:

result = repeatInBackground(inputs);

EDIT 2:

I'm calling execute this way:

AsyncTask mAsyncTask = new ListPalinasAsynkTask(callback);
....
mAsyncTask.execute();

Luca Vitucci · Accepted Answer · 2013-12-08T17:06:12.460

39

Solution found:

the problem was this:

AsyncTask mAsyncTask = new ListPalinasAsynkTask(callback);
....
mAsyncTask.execute();

I'm using generic AsyncTask to call execute, that class would pass Void as a parameter and will never call .execute() on ListPalinasAsynkTask, instead it will call ListPalinasAsynkTask.execute(Void). That gives the error.

Solutions:

Use ListPalinasAsynkTask instead of generic AsyncTask
Better one: Create a new class VoidRepeatableAsyncTask and make other Void AsyncTasks extend that one.

Like this:

public abstract class VoidRepeatableAsyncTask<T> extends RepeatableAsyncTask<Void, Void, T> {
    public void execute() {
        super.execute();
    }
}

Then you can easily use something like this to call execute:

VoidRepeatableAsyncTask mAsyncTask = new ListPalinasAsynkTask(callback);
....
mAsyncTask.execute();

This will call the no-parameters execute method of AsyncTask.

edited Dec 08 '13 at 17:06

answered Dec 08 '13 at 16:58

Luca Vitucci

3,674
4
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60

Perfect solution. The method call `super.execute()` is the important part here. – Mulgard Mar 22 '16 at 08:03
1

your explanation is not correct. correct one is here http://stackoverflow.com/a/34400140/5455629 – q126y Nov 01 '16 at 07:42
the same applies to super.executeOnExecutor(...) - make sure to include "super" to the call if you are overriding AsyncTask – vir us Jun 08 '17 at 16:06
This solution could be way simpler! Just declare it like this: `AsyncTask> asyncTask` – winklerrr Sep 15 '17 at 14:08

score 21 · Answer 2 · answered Apr 06 '14 at 18:03

21

An alternative way with which I solved it is to pass Object in parameters, even if you don't use the parameters.

new AsyncTask<Object, Void, MergeAdapter>()

and the override:

@Override
protected ReturnClass doInBackground(Object... params) {
    //...
}

The above applies (in my case) if you want to pass different types of AsyncTasks to a method and of course you do not care about the parameters.

answered Apr 06 '14 at 18:03

Diolor

13,181
30
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179

Wow. That solved it for me. But I still don't understand why Void as 1st type parameter would give the "java.lang.ClassCastException: java.lang.Object[] cannot be cast to java.lang.Void[]" error. – ConanG Dec 19 '18 at 15:11

score 9 · Answer 3 · answered Nov 15 '14 at 21:01

9

The solution is much simpler as I see it. Just create the subclass object in this way:

AsyncTask<Void, Void, List<Palina> mAsyncTask = new ListPalinasAsynkTask(callback);
....
mAsyncTask.execute();

answered Nov 15 '14 at 21:01

marco

1,686
1
25
33

1

Specifying the generics Type as void for the AsyncTask instead of leaving it off (or in my case as wildcards ,?,?>) solved it for me. – JCricket Dec 28 '14 at 16:44
You forgot an angel bracket – winklerrr Sep 15 '17 at 14:14

score 0 · Answer 4 · answered Dec 08 '13 at 16:22

0

Try using:

result = repeatInBackground((Void) inputs);

instead of

result = repeatInBackground(inputs);

answered Dec 08 '13 at 16:22

Raghav Sood

81,899
22
187
195

That way i won't be able to give a non-Void as input – Luca Vitucci Dec 08 '13 at 16:26
2

@LucaVitucci You ask for a Void as a parameter... You're supposed to give only Void as input – Raghav Sood Dec 08 '13 at 16:28
You're suggesting to edit RepeatableAsyncTask that is a generic class, i'm not asking for Void as parameter, i'm asking for generic parameter A. I'm planning to use this class for non-Void also. – Luca Vitucci Dec 08 '13 at 16:30

Amit · Answer 5 · 2019-11-26T11:22:13.723

If this problem is occurring then you might have created a Derived class object and added its the base class variable (AsyncTask). So this error is occurring.
AsyncTask mAsyncTask = new ListPalinasAsynkTask(callback);

Lint also gives a warning when you do like this "Unchecked call to execute. Params ...."

The solution is ListPalinasAsynkTask mAsyncTask = new ListPalinasAsynkTask(callback); Then call execute on it. It will work fine

Object[] cannot be cast to Void[] in AsyncTask

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