如何在加载GridView时在Scaffold中显示CircularProgressIndicator

import 'package:flutter/material.dart';

bool isLoading = true;

body: isLoading
    ? Center(child: CircularProgressIndicator())
    : GridView.builder(
        gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
          crossAxisCount: 2,
        ),
        itemCount: data.length,
        itemBuilder: (BuildContext context, int index) {
          return GridTile(
            child: Image.network(data[index]),
          );
        },
      ),

// 模拟加载数据的过程
Future.delayed(Duration(seconds: 2), () {
  setState(() {
    isLoading = false;
  });
});