带有片段Activity的TabLayout中的Android进度对话框

Question

我有一个扩展AppCompatActivity的活动。此活动包含工具栏，TabLayout和ViewPager。 我使用带有progressdialog的AsyncTask，我的问题是缺少progressdialog旋转圆圈。

当我从没有工具栏，TabLayout和ViewPager的Activity调用AsyncTask时，旋转圈不会丢失。

谢谢。

public class YiOptionalInfoActivity extends AppCompatActivity implements View.OnClickListener, YiAsyncTaskListener{

private Toolbar toolbar;
private TabLayout tabLayout;
private ViewPager viewPager;


private Button mBtnNext = null;
private YiAsyncTask mAsyncTask = null;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.optional_screen);

    toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    //getSupportActionBar().setTitle(R.string.optional_info);
    getSupportActionBar().setDisplayShowTitleEnabled(false);

    viewPager = (ViewPager) findViewById(R.id.viewpager);
    setupViewPager(viewPager);

    tabLayout = (TabLayout) findViewById(R.id.tabs);
    tabLayout.setupWithViewPager(viewPager);
    setupTabIcons();

}



public class YiAsyncTask extends AsyncTask<Integer, Void, Boolean> {


private final String TAG = YiAsyncTask.class.getSimpleName();

/** progress dialog to show user that the backup is processing. */
private ProgressDialog mProgressDialog = null;
/** application context. */
private Context mContext = null;

public YiAsyncTask(Context context) {
    this.mContext = context;
}


protected void onPreExecute() {
    super.onPreExecute();
    mProgressDialog = this.mProgressDialog.show(mContext, mContext.getString(R.string.app_name), mContext.getString(R.string.task_processing), true);
}

@Override
protected void onPostExecute(final Boolean success) {
    if (null != mProgressDialog && mProgressDialog.isShowing()) {
        mProgressDialog.dismiss();
        mProgressDialog = null;
    }
}

@Override
protected Boolean doInBackground(Integer... params) {
}