Flutter中自定义提示框

1. 弹出提示框

定义模态框组件，代码如下：

import 'package:flutter/material.dart';
class MyDialog extends Dialog{

    final String title;
    final String content;

    // 构造函数赋值
    MyDialog({this.title="",this.content=""});

    @override
    Widget build(BuildContext context) {

        return Material(
            type:MaterialType.transparency,
            child:Center(
                child:Container(
                    width:300,
                    height:300,
                    color:Colors.white,
                    child:Column(
                        children: [
                            Padding(
                                padding: EdgeInsets.all(10),