局部更新有好几种方法，本次使用的是 StatefulBuilder 定义 customState去更新对话框内容

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';

class ProgressDialog {
  final BuildContext context;
  BuildContext? dialogContext;
  double _progress = 0.0;
  bool _isShowing = false;
  StateSetter? mCustomState;

  ProgressDialog(this.context, this._progress);

  void show() {
    _isShowing = true;
    showDialog<void>(
      context: context,
      builder: (BuildContext context) {
        return StatefulBuilder(builder: (mDialogContext, customState) {
          mCustomState =customState;
          dialogContext = mDialogContext;
          return AlertDialog(
            title: const Text('下载中...'),
            content: Column(
              mainAxisSize: MainAxisSize.min,
              children: <Widget>[
                LinearProgressIndicator(value: _progress),
                Padding(
                  padding: const EdgeInsets.symmetric(vertical: 20.0),
                  child: Text('${(_progress * 100).toStringAsFixed(0)}%'),
                ),
              ],
            ),
          );
        });
      },
    );
  }

  void updateProgress(double progress) {
    if (_isShowing && null!=mCustomState) {
      (mCustomState!)(() {
        _progress = progress;
      });
    }
  }

  void hide() {
    if (dialogContext != null && _isShowing) {
      Navigator.of(dialogContext!).pop();
    }
    _isShowing = false;
  }

}

定义 StateSetter? mCustomState; 去set更新

使用

   final ProgressDialog progressDialog = ProgressDialog(context, 0);
    progressDialog.show();


 更新进度
progressDialog.updateProgress(progress);

关闭对话框
progressDialog.hide();