如何在 Flutter Z4E9F7F44562A881ZFE61E0DABFFE0AC02 中为 Json object 创建事件侦听器

Question

i would like to know how i can listen to json objects in my gridview so that i can use them for navigation logic.Forexample picking a category id of a gridview item and using it to display it's respective data or items in the next page.

Answer 1

You can fetch the list to be shown in GridView from the network.

getTags() async {
 var res = await Client().getAsync("yourURL");
 var decodedJson = jsonDecode(res.body);

 setState(() {
      tagList = decodedJson;
    });
 }

Now you can use GridView.builder and InkWell to navigate to another screen.

 GridView.builder(
                  gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
                    crossAxisCount: 2,
                    childAspectRatio: MediaQuery.of(context).size.width /
                        ((MediaQuery.of(context).size.height) / 2),
                  ),
                  itemCount: tagList.length,
                  itemBuilder: (BuildContext context, int index) {
                    Tag tag = (tagList)[index];

                    return InkWell(
                     onTap:(){
                      Navigator.push(
                       context,
                       MaterialPageRoute(builder: (context) => 
                         YourPageClass(yourId: tag.id)),
                       );
                     },
                     child: Container()


                   )
                  },
                ),

Here is the code for the Tag class.

class Tag {
    int id;
    Tag({this.id,});

    Tag.fromJson(Map<String, dynamic> json) {
     id = json['id'];
    }

    Map<String, dynamic> toJson() {
      final Map<String, dynamic> data = new Map<String, dynamic>();
      data['id'] = this.id;

      return data;
    }
   }

Answer 2

Final Output:

Full working code:

import 'package:flutter/material.dart';

/* This is the data that we are going to use to render the grid of products using Gridview.
As pointed out by Pranay, you can use the fetched data from a remote server. 
but for the sake of simplicity, I am using hardcoded data. 
*/

List data = [
  {
    "id": 1,
    "name": "Mix Pina Colada 1",
    "desc": "Ice Cream Bar - Oreo Cone 1",
    "image": "http://dummyimage.com/110x138.png/dddddd/000000",
    "price": 93,
    "quantity": 0,
  },
  {
    "id": 2,
    "name": "Cake - Bande Of Fruit",
    "desc": "Cheese - Cheddar With Claret",
    "image": "http://dummyimage.com/172x223.png/cc0000/ffffff",
    "price": 4,
    "quantity": 0,
  },
  {
    "id": 3,
    "name": "Lid Coffee Cup 8oz Blk",
    "desc": "Rosemary - Primerba, Paste",
    "image": "http://dummyimage.com/110x243.png/ff4444/ffffff",
    "price": 18,
    "quantity": 0,
  },
];

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'GridView Example'),
    );
  }
}

class MyHomePage extends StatelessWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;
  List products = data;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.amber,
      appBar: AppBar(
        title: Text(title),
      ),
      body: GridView.count(
        primary: false,
        padding: const EdgeInsets.all(20),
        crossAxisSpacing: 10,
        mainAxisSpacing: 10,
        crossAxisCount: 2,
        children: products.map((product) {
          print(product["name"]);
          return InkWell(
            onTap: () {
             /* Using Navigator we will navigate to DetailsScreen, 
             along with it we will also pass the product object which 
             will be used to render the product details of the clicked item 
             */
              Navigator.push(
                context,
                MaterialPageRoute(
                  builder: (context) => DetailsScreen(
                    product: product,
                  ),
                ),
              );
            },
            child: Container(
                color: Colors.white,
                padding: EdgeInsets.all(10),
                child: Text(product["name"])),
          );
        }).toList(),
      ),
    );
  }
}

/*
The following widget tasked the product object that we passed in 
Navigator, and displays the data of that particular product.
*/

class DetailsScreen extends StatelessWidget {
  final dynamic product;
  DetailsScreen({this.product});
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text(product["name"])),
      body: Column(
        children: [
          Image.network(
            product["image"],
            width: double.infinity,
            height: 200,
            color: Colors.amberAccent,
          ),
          Text("Name: " + product["name"]),
          Text("Description: " + product["desc"]),
          Text("Price: " + product["price"].toString()),
        ],
      ),
    );
  }
}