java.lang.RuntimeException: An error occured while executing doInBackground()
            at android.os.AsyncTask$3.done(AsyncTask.java:299)
            at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352)
            at java.util.concurrent.FutureTask.setException(FutureTask.java:219)
            at java.util.concurrent.FutureTask.run(FutureTask.java:239)
            at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
            at java.lang.Thread.run(Thread.java:856)
     Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
            at android.os.Handler.<init>(Handler.java:197)
            at android.os.Handler.<init>(Handler.java:111)
            at android.view.ViewRootImpl$ViewRootHandler.<init>(ViewRootImpl.java:2802)
            at android.view.ViewRootImpl.<init>(ViewRootImpl.java:3105)
            at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:216)
            at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:69)
            at android.app.Dialog.show(Dialog.java:303)
            at ru.korshun.cobaguardidea.app.Root$CheckDirectoryExist.onPreExecute(Root.java:962) //this.pd.show();
            at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:586)
            at android.os.AsyncTask.execute(AsyncTask.java:534)
            at ru.korshun.cobaguardidea.app.Root$CheckDirectoryExist.doInBackground(Root.java:980)
            at ru.korshun.cobaguardidea.app.Root$CheckDirectoryExist.doInBackground(Root.java:942)
            at android.os.AsyncTask$2.call(AsyncTask.java:287)
            at java.util.concurrent.FutureTask.run(FutureTask.java:234)
            at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
            at java.lang.Thread.run(Thread.java:856)

@Override
protected void onCreate(Bundle savedInstanceState) {
....
new CheckDirectoryExist(new ProgressDialog(this)).execute();
....
}

    class CheckDirectoryExist
            extends AsyncTask<Void, Void, Boolean> {

        private ProgressDialog pd;

        CheckDirectoryExist(ProgressDialog pd) {
            this.pd = pd;

            this.pd.setTitle(Root.PD_TITLE);
            this.pd.setMessage("Files indexing ...");

            this.pd.setCancelable(false);
        }

        @Override
        protected void onPreExecute() {
            this.pd.show(); //Дальше этого не идет
        }
}