Flutter 在尝试从 php 后端获取数据时返回 null

Question

这是我的前端代码。 我对这里可能发生的事情感到非常沮丧。

我想从服务器端 php 代码收集数据到 flutter 应用程序。

负责此连接的函数位于 MyScaffold 类中的 Future _getPosts() 函数中。

class MyScaffold extends StatelessWidget{
  @override
  Widget build(BuildContext context){
  return Scaffold(
        appBar: AppBar(
          title: Text("ENPOWER DISCUSSION"),
          backgroundColor: Colors.green,
        ),
        drawer: Drawer(
        child: ListView(
          children: <Widget>[
            ListTile(
              title: Text("GENERAL FEEDS"),
              onTap:(){
                Navigator.of(context).pop(); //
              }
            ),
            ListTile(
              title: Text("ENROLLMENT"),
              onTap:(){
                Navigator.of(context).pop(); // Close Navigator
                //Call a new function here

                Navigator.push(
                  context,
                  MaterialPageRoute(builder: (context) => EnrollmentPage()),
                );                
              }              

            ),
            ListTile(
              title: Text("PAYMENT"),
              onTap:(){
                Navigator.of(context).pop(); // Close Navigator
                //Call a new function here

                Navigator.push(
                  context,
                  MaterialPageRoute(builder: (context) => PaymentPage()),
                );                
              }
            ),
            ListTile(
              title: Text("FAQ"),
              onTap:(){
                Navigator.of(context).pop(); // Close Navigator
                //Call a new function here
                Navigator.push(
                  context,
                  MaterialPageRoute(builder: (context) => FaqPage()),
                );
              }
            ),                                    
          ],
        ),
      ), 
      body: Container(
        child: FutureBuilder(
          future: _getPosts(),
          builder: (BuildContext context, AsyncSnapshot snapshot){
            print(snapshot.data);
            if(snapshot.data == null){
              return Container(
                child: Center(child: Text("Processing..."),),
              );
            }else{
              return ListView.builder(itemCount: snapshot.data.length,
                itemBuilder: (BuildContext context, int index){
                  return ListTile(
                    title: Text(snapshot.data[index].postTitle),
                  );
                },
              );
            }
          },
        ),
      ),       
      );

  }

  Future<List<Post>> _getPosts() async{
    var data = await http.get("www.empowermentopportunities.com/xxyyzz/admin_panel/backend/api_connector.php");
    var jsonData = json.decode(data.body);

    List<Post> posts = [];

    for(var p in jsonData){
      Post post = Post(p["post_id"], p["post_title"], p["post_content"], p["post_image_url"], p["post_date"]);
      posts.add(post);
    }

    print(posts.length);
    return posts;
  }

}


class Post{
  final int postId;
  final String postTitle;
  final String postContent;
  final String postImageurl;
  final String postDate;

  Post(this.postId, this.postTitle, this.postContent, this.postImageurl, this.postDate);
}
void main(){
  runApp(MaterialApp(
    title: 'My app',
    home: MyScaffold(),
  ));
}

这是服务器端php代码，其作用是从数据库中收集数据，然后将其压缩为JSON，然后再发送给前端调用者。

function fetch_gen_data($offset, $total){
    include "../db/connection.php";
    $data = array();

    $query = mysqli_query($con, "SELECT * FROM posts ORDER BY post_id DESC LIMIT $total OFFSET $offset")or die(mysqli_error($con));

    if(mysqli_num_rows($query)>0){

            while($row = mysqli_fetch_assoc($query)){
                $data[] = $row;



            }


    }
    return json_encode(json_encode($data));
}

然后我从另一个调用该函数

echo fetch_gen_data(0, 10);

Answer 1

我认为问题在于后端的双 json 编码。 如果您看到响应是字符串而不是 json。

只需通过浏览器访问 http://www.empowermentopportunities.com/xxyyzz/admin_panel/backend/api_connector.php ，您就会看到。

返回应该是return json_encode($data);