java - WorkManager 找不到所需的零参数构造函数

Question

我正在使用在 android.arch.work:work-runtime 依赖项中找到的 WorkManager 1.0.0-alpha02 来查询一个每分钟网页一次(查询代码被排除在这个例子中，因为它不相关)。

当我像这样使用 WorkManager 时:

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;
        }
}

它给出了这个错误信息:

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

我试过以下构造函数都无济于事:

• 没有构造函数
• 公开
• 私有(private)
• 具有非空主体的构造函数，唯一的语句为 super();

Answer 1

从 MessageWorker 中删除以下构造函数并使类public。 :

public MessageWorker() {
}

还要确保类在单独的文件中。