使用 GSON 和 Volley 在 Android 上显示 JSON 数据

Posted 2023-02-26

【中文标题】使用 GSON 和 Volley 在 Android 上显示 JSON 数据

【英文标题】：Display JSON data on Android using GSON and Volley

【发布时间】：2017-06-30 08:36:39

【问题描述】：

您好，我是 android 编程新手，正在努力学习它。我遵循this 教程，它工作正常，但是我不知道如何在列表视图中显示记录。

PostActivity.java 文件来自下面的教程，

package com.kylewbanks.gsonvolleytutorial;

    import android.app.Activity;
    import android.os.Bundle;
    import android.util.Log;
    import android.widget.ArrayAdapter;

    import com.android.volley.Request;
    import com.android.volley.RequestQueue;
    import com.android.volley.Response;
    import com.android.volley.VolleyError;
    import com.android.volley.toolbox.StringRequest;
    import com.android.volley.toolbox.Volley;
    import com.google.gson.Gson;
    import com.google.gson.GsonBuilder;

    import java.util.ArrayList;
    import java.util.Arrays;
    import java.util.List;

    import static android.R.id.list;

    public class PostActivity extends Activity 

        private static final String ENDPOINT = "https://kylewbanks.com/rest/posts.json";

        private RequestQueue requestQueue;
        private Gson gson;

        @Override
        protected void onCreate(Bundle savedInstanceState) 
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_post);

            requestQueue = Volley.newRequestQueue(getApplicationContext());
            GsonBuilder gsonBuilder = new GsonBuilder();
            gsonBuilder.setDateFormat("M/d/yy hh:mm a");
            gson = gsonBuilder.create();

            fetchPosts();
        

        private void fetchPosts() 
            StringRequest request = new StringRequest(Request.Method.GET, ENDPOINT, onPostsLoaded, onPostsError);

            requestQueue.add(request);
        

        private final Response.Listener<String> onPostsLoaded = new Response.Listener<String>() 
            @Override
            public void onResponse(String response) 
                //Log.i(PostActivity.class.getSimpleName(), response);

                List<Post> posts = Arrays.asList(gson.fromJson(response, Post[].class));
                //Log.i(PostActivity.class.getSimpleName(), posts.size() + " posts loaded.");

                List listview = (List) findViewById(R.id.postListView);

                for (Post post : posts) 
                    //Log.i(PostActivity.class.getSimpleName(), post.ID + ": " + post.title);
                
                ArrayAdapter adapter = new ArrayAdapter(this,R.layout.single_post_item, posts);
                listview.setAdapter(adapter);

            
        ;

        private final Response.ErrorListener onPostsError = new Response.ErrorListener() 
            @Override
            public void onErrorResponse(VolleyError error) 
                Log.e(PostActivity.class.getSimpleName(), error.toString());
            
        ;
    

Post.java

import java.util.Date;
import com.google.gson.annotations.SerializedName;

public class Post 

    @SerializedName("id")
    long ID;

    @SerializedName("date")
    Date dateCreated;

    String title;
    String author;
    String url;
    String body;

activity_post.xml

<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_
    android:layout_
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context=".PostActivity">

    <ListView
        android:layout_
        android:layout_
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:id="@+id/postListView"
        android:layout_alignParentBottom="true" />
</RelativeLayout>

single_post_item.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_
    android:layout_>

    <TextView
        android:text="TextView"
        android:layout_
        android:layout_
        android:id="@+id/textView" />
</LinearLayout>

更新错误 1：

:app:processDebugManifest
:app:processDebugResources
AGPBI: "kind":"error","text":"Error parsing XML: XML or text declaration not at start of entity","sources":["file":"C:\\Users\\xxx\\Downloads\\GSONVolleyTutorial-master\\GSONVolleyTutorial-master\\app\\src\\main\\res\\layout\\activity_post.xml","position":"startLine":0],"original":"","tool":"AAPT"
AGPBI: "kind":"error","text":"Error parsing XML: XML or text declaration not at start of entity","sources":["file":"C:\\Users\\xxx\\Downloads\\GSONVolleyTutorial-master\\GSONVolleyTutorial-master\\app\\src\\main\\res\\layout\\single_post_item.xml","position":"startLine":0],"original":"","tool":"AAPT"
C:\Users\xxx\Downloads\GSONVolleyTutorial-master\GSONVolleyTutorial-master\app\build\intermediates\res\merged\debug\layout\activity_post.xml:1: error: Error parsing XML: XML or text declaration not at start of entity

C:\Users\xxx\Downloads\GSONVolleyTutorial-master\GSONVolleyTutorial-master\app\build\intermediates\res\merged\debug\layout\single_post_item.xml:1: error: Error parsing XML: XML or text declaration not at start of entity

 FAILED

FAILURE: Build failed with an exception.

更新错误 2：

C:\Users\xxx\Downloads\GSONVolleyTutorial-master\GSONVolleyTutorial-master\app\src\main\java\com\kylewbanks\gsonvolleytutorial\PostActivity.java:70: error: no suitable constructor found for ArrayAdapter(<anonymous Listener<String>>,int,int,List<String>)
                ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,R.layout.single_post_item,R.id.textView, posts_strs);
                                               ^
    constructor ArrayAdapter.ArrayAdapter(Context,int,int,String[]) is not applicable
      (argument mismatch; <anonymous Listener<String>> cannot be converted to Context)
    constructor ArrayAdapter.ArrayAdapter(Context,int,int,List<String>) is not applicable
      (argument mismatch; <anonymous Listener<String>> cannot be converted to Context)
Note: Some messages have been simplified; recompile with -Xdiags:verbose to get full output
1 error

:app:compileDebugJavaWithJavac FAILED

FAILURE: Build failed with an exception.

【问题讨论】：

为什么是 Post[].class 而不是 Post.class？

可以添加single_post_item.xml的源码吗？

我添加了所有文件@GaëtanMaisse

我对 android 编程非常陌生，所以这就是我在教程中得到的 link@Nirel

【参考方案1】：

由于您的列表布局中只有一个TextView，因此您打算显示单个项目

1.) 创建一个String 数组列表并向其中添加元素

2.) 在创建适配器时提及@+id/textView" 作为第三个参数

ArrayAdapter(Context context, int resource, int textViewResourceId, List<T> objects)

public class PostActivity extends Activity 

    private static final String ENDPOINT = "https://kylewbanks.com/rest/posts.json";

    private RequestQueue requestQueue;
    private Gson gson;
    private List<String> posts_strs ;

    // keep it here for later use in other methods
    private List<Post> posts ;

    @Override
    protected void onCreate(Bundle savedInstanceState) 
        super.onCreate(savedInstanceState);
        // code

        // initialize list
        posts_strs = new ArrayList<String>();

        // code
    


    private final Response.Listener<String> onPostsLoaded = new Response.Listener<String>() 
        @Override
        public void onResponse(String response) 
            //Log.i(PostActivity.class.getSimpleName(), response);

            posts = Arrays.asList(gson.fromJson(response, Post[].class));
            //Log.i(PostActivity.class.getSimpleName(), posts.size() + " posts loaded.");

            List listview = (List) findViewById(R.id.postListView);

            for (Post post : posts) 
                 // add items to list
                 posts_strs.add( post.ID + ": " + post.title);
                //Log.i(PostActivity.class.getSimpleName(), post.ID + ": " + post.title);
            
            ArrayAdapter<String> adapter = new ArrayAdapter<String>(PostActivity.this,R.layout.single_post_item
                     ,R.id.textView, posts_strs);
            //   use the textview id posts_strs while creating adapter
            listview.setAdapter(adapter);

        
    ;
        // code

问题：

1.) 在XML 布局activity_post 和single_post_item 的顶部添加<?xml version="1.0" encoding="utf-8"?>

2.) 使用PostActivity.this 而不是this，因为this 将引用匿名Response.Listener<String> 类而不是PostActivity。

【讨论】：

尝试更新后的代码，如果有错误，请提供详细信息

你必须在适配器中使用posts_strs 我及时在我的代码中更新了这个，只需尝试当前代码，肯定可以工作

我尝试了更新的代码，但错误如下：C:\Users\xxx\Downloads\GSONVolleyTutorial-master\GSONVolleyTutorial-master\app\src\main\res\layout\activity_post.xml 和 C:\Users\xxx\Downloads\GSONVolleyTutorial-master\GSONVolleyTutorial-master\app\src\main\res\layout\single_post_item.xml @Pavneet Singh

在你的帖子最后发布完整的错误，这些行只是路径，有有用的错误细节

是的，感谢您提供当前代码，它运行良好，我需要做一些如何使用 POST 方法并将操作和 id 参数发送到接受 post 请求的服务器。例如，我需要发送 operation=show,id=1 来获取 id 为 1 的列表 @Pavneet Singh

【参考方案2】：

C:\Users\xxx\Downloads\GSONVolleyTutorial-master\GSONVolleyTutorial-master\app\src\main\java\com\kylewbanks\gsonvolleytutorial\PostActivity.java:70: error: no suitable constructor found for ArrayAdapter(<anonymous Listener<String>>,int,int,List<String>)
                ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,R.layout.single_post_item,R.id.textView, posts_strs);
                                               ^
    constructor ArrayAdapter.ArrayAdapter(Context,int,int,String[]) is not applicable
      (argument mismatch; <anonymous Listener<String>> cannot be converted to Context)
    constructor ArrayAdapter.ArrayAdapter(Context,int,int,List<String>) is not applicable
      (argument mismatch; <anonymous Listener<String>> cannot be converted to Context)

由于创建ArrayAdapter 的代码位于匿名内部类中，因此this 指的是该匿名类的实例。要访问包含匿名类的PostActivity 实例的this 指针，请改用PostActivity.this。