flutter 自定義loading

使用:
LoadingView.showSerially(context);
LoadingView.showDiscrete(context);
源碼:
LoadingView.showSerially(context);

import 'dart:async';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'dart:math' as math;

class LoadingView {

  static LoadingView _instance;
  static LoadingView instance() {
    if(_instance == null) {
      _instance = LoadingView();
    }
    return _instance;
  }

  SeriallyLoadingView _seriallyLoadingView;
  DiscreteLoadingView _discreteLoadingView;
  OverlayEntry _discreteOverlayEntry;
  OverlayEntry _seriallyOverlayEntry;
  int _rotationType = 0;

  OverlayEntry discreteOverlayEntry() {
    if(_discreteOverlayEntry == null) {
      _discreteOverlayEntry = _createDiscreteOverlayEntry();
    }
    return _discreteOverlayEntry;
  }

  OverlayEntry seriallyOverlayEntry() {
    if(_seriallyOverlayEntry == null) {
      _seriallyOverlayEntry = _createSeriallyOverlayEntry();
    }
    return _seriallyOverlayEntry;