CODEWITHSUNDEEP
javaandroidandroid-workmanager
Neel
Neel

Reputation: 43

WorkManager cannot find required zero-argument constructor

I'm using WorkManager 1.0.0-alpha02 found in the android.arch.work:work-runtime dependency to query a web page every one minute (the querying code is excluded for this example as it's irrelevant).

When I use WorkManager like this:

WorkManager
                .getInstance()
                .enqueue(
                        new PeriodicWorkRequest.Builder(
                                MessageWorker.class,
                                1,
                                TimeUnit.MINUTES
                        )
                                .setConstraints(
                                        new Constraints.Builder()
                                                .setRequiredNetworkType(NetworkType.CONNECTED)
                                                .build()
                                )
                                .build()
                );

private class MessageWorker extends Worker {
        public MessageWorker() {
        }

        @NonNull
        @Override
        public WorkerResult doWork() {
            // Do stuff
            return WorkerResult.SUCCESS;
        }
}

it gives this error message:

05-31 17:50:05.645 11749-12168/com.neelkamath.webview E/WorkerWrapper: Trouble instantiating com.neelkamath.webview.MainActivity$MessageWorker
    java.lang.InstantiationException: java.lang.Class<com.neelkamath.webview.MainActivity$MessageWorker> has no zero argument constructor
        at java.lang.Class.newInstance(Native Method)
        at androidx.work.impl.WorkerWrapper.workerFromClassName(WorkerWrapper.java:405)
        at androidx.work.impl.WorkerWrapper.workerFromWorkSpec(WorkerWrapper.java:377)
        at androidx.work.impl.WorkerWrapper.run(WorkerWrapper.java:132)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1162)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:636)
        at java.lang.Thread.run(Thread.java:764)
05-31 17:50:05.645 11749-12168/com.neelkamath.webview E/WorkerWrapper: Could for create Worker com.neelkamath.webview.MainActivity$MessageWorker

I have tried the following constructors to no avail:

Upvotes: 4

Views: 1270

Answers (2)

Liang HAN
Liang HAN

Reputation: 39

You can create the MessageWorker class in separate file, and if you want to make MessageWorker class as nested class, you can also make it static:

public static class MessageWorker extends Worker {
    @NonNull
    @Override
    public WorkerResult doWork() {
        // Do stuff
        return WorkerResult.SUCCESS;
    }
}

The reason is the WorkerWrapper will create your worker instance by clazz.newInstance(), and there is no zero argument constructor for nested class

Upvotes: 1

Sagar
Sagar

Reputation: 24907

Remove following constructor from MessageWorker and make the class public. :

public MessageWorker() {
}

Also ensure class is in separate file.

Upvotes: 2

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