Android 日期选择器上部为空

我正在以以下方式使用Android的原生DatePicker，它工作正常，但视图不太合适

public class DatePickerFragment extends DialogFragment
        implements DatePickerDialog.OnDateSetListener {

    DatePickerDialog dialog;

    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        // Use the current date as the default date in the picker
        final Calendar c = Calendar.getInstance();
        int year = c.get(Calendar.YEAR);
        int month = c.get(Calendar.MONTH);
        int day = c.get(Calendar.DAY_OF_MONTH);

        dialog= new DatePickerDialog(getActivity(), this, year, month, day);
        dialog.getDatePicker().setMinDate(new Date().getTime());
        // Create a new instance of DatePickerDialog and return it
        return dialog;
    }

    public void onDateSet(DatePicker view, int year, int month, int day) {
        // Doing some stuff here
    }
}

这样称呼：

DialogFragment datePickerFragment = new DatePickerFragment();
datePickerFragment.show(getActivity().getFragmentManager(), "startDate");

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我通过从v21/styles.xml文件中删除这一行，解决了我的问题

<style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
    <!--<item name="android:background">@android:color/white</item>-->
</style>

由于这一行，所有自定义视图（片段、对话框等）默认选择白色背景