Flutter失败的断言：第513行pos 14：'file！= null'：不正确

Question

我一直在尝试运行flutter应用程序，并且该应用程序不断显示失败的断言错误。下面是我的代码

import 'package:flutter/material.dart';
import 'package:flutter/material.dart' as prefix0;
import 'package:image/image.dart';
import 'dart:io';
import 'package:simple_permissions/simple_permissions.dart';

import 'package:image/image.dart' as IO;



void main () async{
  await SimplePermissions.requestPermission(permissionFromString('Permission.WriteExternalStorage'));
  await SimplePermissions.requestPermission(permissionFromString('Permission.ReadExternalStorage'));
  runApp(MaterialApp(home: ImageDisplay(),));

}
Permission permissionFromString(String value){
  Permission permission;
  for (Permission item in Permission.values){

    if(item.toString()== value){
      permission =item;
    }
  }
  return permission;
}

class ImageDisplay extends StatelessWidget{

  File ReadFile (){
    IO.Image image = IO.readJpg(new File('/storage/emulated/0/Pictures/1575528198764.jpg').readAsBytesSync());
    try {
      IO.Image thumbnail = IO.copyCrop(image, 60, 60, 300, 200);
      //File('/storage/emulated/0/Pictures/${thumbnail}.jpg')
     // ..createSync(recursive: true)
     //   ..writeAsBytesSync(writeJpg(thumbnail));

      File img = new File('/storage/emulated/0/Pictures/1575528198764.jpg');
      return img;
    }catch (e){
      print(e);
    }



  }

  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return new Scaffold(
      body:new Center(
        child: new SizedBox(child: prefix0.Image.file(ReadFile()),
        )

      ) ,
    );
  }
}

错误有此行 'package：flutter / src / painting / image_provider.dart'：断言失败：513行pos 14：'file！= I / flutter（28465）：null'：不正确。

Answer 1

child: new SizedBox(child: prefix0.Image.file(ReadFile()),

因此，在这一行中，您要放置Image.file（ReadFile（）），但是返回的对象是 null 。