Flutter why does gesturedetector flutter doesn't work?

Question

so the title always changes but at the appBar but I don't want that the title to change on the Appbar I want that the title changes in the SizedBox but there is always just written "Smoothie-Bowl"

In the picture "whatImean" the text above the blue line shouldn't change and the text above the red line should change

import 'package:flutter/material.dart';
import 'Sachen.dart';
import 'dart:math';


class Rezept extends StatelessWidget{
  final String rezept;
  Rezept(this.rezept);


  @override
  Widget build(BuildContext context) {
   return Scaffold(
      appBar: AppBar(
        backgroundColor: const Color(0xFF4caf50),
        title: Text(rezept),
        foregroundColor: Colors.white,
        titleTextStyle: const TextStyle(
          fontWeight: FontWeight.bold,
          fontSize: 20,
        ),
      ),
      body: RezeptPage(),
    );
  }
}



class RezeptPage extends StatefulWidget {
  const RezeptPage ({Key? key}) : super(key: key);

  @override
  _RezeptPageState createState() => _RezeptPageState();
}

class _RezeptPageState extends State<RezeptPage> {
  int PiNumber = 1;


  void changeDiceNumber() {
    setState(() {
      PiNumber = Random().nextInt(4) +1;
    });
  }


  final List<Sachen> infoBank = [
    Sachen(title: "Schoko-Bowl", image: Image.asset("Images/frue1.png"), text: '-Mehl'),
    Sachen(title: "Smoothie-Bowl", image: Image.asset("images/frue2.png"), text: '-Zucker'),
    Sachen(title: "Porridge", image: Image.asset("images/frue3.png"), text: '-Milch'),
    Sachen(title: "Porridge", image: Image.asset("images/frue4.png"), text: '-Eier'),
    Sachen(title: "Schoko Mousse", image: Image.asset("images/frue5.png"),text: '-Butter'),

  ];


  @override
  Widget build(BuildContext context) {
    return ListView(
      children: <Widget>[
        SizedBox(
          child: Padding(
            padding: EdgeInsets.fromLTRB(10, 15, 10, 15),
            child: Card(
              elevation: 8,
              child: ListTile(
                title: Center(
                  child: Text(infoBank[PiNumber].title,
                    style: const TextStyle(
                      fontSize: 20.0,
                      fontWeight: FontWeight.bold,
                    ),
                  ),
                ),
              ),
            ),
          ),
        ),
        SizedBox(
          width: 350,
          height: 500,
          child: Card(
            elevation: 5,
            margin: EdgeInsets.fromLTRB(10, 5, 10, 20),
            child: Padding(
              padding: EdgeInsets.fromLTRB(15, 15, 10, 0),
              child: RichText(text: const TextSpan(
                text: 'Zutaten:',
                style: TextStyle(
                  fontWeight: FontWeight.bold,
                  color: Colors.black,
                  fontSize: 22.0,
                  decoration: TextDecoration.underline,
                  decorationThickness: 2.0,
                ),
                children: <TextSpan>[
                  TextSpan(
                    text: '\n\n-Mehl' '\n-Zucker' '\n-Milch' '\n-Eier' '\n-Butter',
                    style: TextStyle(
                      fontSize: 18,
                      fontWeight: FontWeight.normal,
                      decoration: TextDecoration.none,
                    ),
                  ),
                  TextSpan(
                    text: '\n\nZubereitung:',
                  ),
                  TextSpan(
                    text: '\n\n-Zuerst vermischen wir alles' '\n-Anschließend wird es in der Pfanne angebraten' '\n-Zuletzt mit Schokolade bestreichen und genießen',
                    style: TextStyle(
                      fontSize: 18,
                      fontWeight: FontWeight.normal,
                      decoration: TextDecoration.none,
                    ),
                  ),
                ],
              ),
              ),
            ),
          ),
        ),
      ],
    );
  }
}

import 'dart:math';
import 'package:essen/Rezept.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'Sachen.dart';





class Categories extends StatelessWidget{
  final String name;
  Categories(this.name)
  ;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: const Color(0xFF4caf50),
        title: Text(name),
        foregroundColor: const Color(0xFFeceff1),
      ),
      body: const DicePage(),
    );
  }
}

class DicePage extends StatefulWidget {
  const DicePage({Key? key}) : super(key: key);

  @override
  _DicePageState createState() => _DicePageState();
}

class _DicePageState extends State<DicePage> {
  int PicNumber = 1;
  int PiNumber =1;

  void changeDiceNumber() {
    setState(() {
      PicNumber = Random().nextInt(4) +1;
      PiNumber = Random().nextInt(4) +1;
    });
  }



  final List<Sachen> infoBank = [
    Sachen(title: "Schoko-Bowl", image: Image.asset("Images/frue1.png"), text: '-Mehl'),
    Sachen(title: "Smoothie-Bowl", image: Image.asset("images/frue2.png"), text: '-Zucker'),
    Sachen(title: "Porridge", image: Image.asset("images/frue3.png"), text: '-Milch'),
    Sachen(title: "Porridge", image: Image.asset("images/frue4.png"), text: '-Eier'),
    Sachen(title: "Schoko Mousse", image: Image.asset("images/frue5.png"),text: '-Butter'),

  ];


  @override
  Widget build(BuildContext context) {
    return Center(
      child: Column(
        children: [
          Card(
            margin: const EdgeInsets.fromLTRB(50, 35, 50, 0),
            elevation: 15,
            color: const Color(0xFF4caf50),
            child: SizedBox(
              height: 80,
              width: 180,
              child: Center(
                child: Padding(
                  padding: const EdgeInsets.symmetric(vertical: 10, horizontal: 18),
                  child: Center(
                    child: GestureDetector(
                      onTap: () {
                        Navigator.of(context).push(
                          MaterialPageRoute(builder: (context) => Rezept(infoBank[PicNumber].title,
                          ),
                          ),
                        );
                      },
                      child: Text(infoBank[PicNumber].title,
                        style: const TextStyle(
                          fontSize: 20,
                          fontWeight: FontWeight.bold,
                          color: Colors.white,
                        ),
                      ),
                    ),
                  ),
                ),
              ),
            ),
          ),
          Row(
            children: [
              Expanded(
                child: TextButton(
                  onPressed: () {
                    setState(() {
                      PicNumber++;
                    });
                    changeDiceNumber();
                    print('LeftDiceNumber = $PicNumber');
                  },
                  child: Container(
                    height: 415,
                    width: 350,
                    margin: const EdgeInsets.fromLTRB(10, 20, 10, 20),
                    decoration: BoxDecoration(
                      border: Border.all(
                        width: 3,
                        color: Colors.grey.shade700,
                      ),
                    ),
                    child: FittedBox(
                      child: infoBank[PicNumber].image,
                      fit: BoxFit.fill,
                      clipBehavior: Clip.hardEdge,
                    ),
                  ),
                ),

              ),
            ],
          ),
        ],
      ),
    );
  }
}