无法显示Json数据 [英] Unable to display Json data
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问题描述
我正在尝试显示json对象内部的json数组，但文本视图上未显示任何内容.我调试了一下，发现info.java类工作正常.如果我在info.java类中传递了简单的字符串值(在删除json解析后的java代码之后)，则它起作用了，但我无法传递json数据. Singleton.java
I am trying to display json array which is inside a json object but nothing is displaying on the text view. I debugged and found that info.java class is working fine. If i am passing the simple string value(after removing the json parsing java code) in the info.java class it's working but i am unable to pass json data.
Singleton.java
package com.example.osama.recyclerthug;
import android.content.Context;
import android.graphics.Bitmap;
import android.support.v4.util.LruCache;
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.toolbox.ImageLoader;
import com.android.volley.toolbox.Volley;
public class Singleton {
private static Singleton mInstance;
private RequestQueue mRequestQueue;
private ImageLoader mImageLoader;
private static Context mCtx;
private Singleton(Context context){
mCtx = context;
mRequestQueue =getRequestQueue();
mImageLoader = new ImageLoader(mRequestQueue,
new ImageLoader.ImageCache() {
private final LruCache<String, Bitmap>
cache = new LruCache<String, Bitmap>(20);
@Override
public Bitmap getBitmap(String url) {
return cache.get(url);
}
@Override
public void putBitmap(String url, Bitmap bitmap) {
cache.put(url, bitmap);
}
});
}
public static synchronized Singleton getInstance(Context context){
if (mInstance == null){
mInstance = new Singleton(context);
}
return mInstance;
}
public RequestQueue getRequestQueue(){
if (mRequestQueue == null){
mRequestQueue = Volley.newRequestQueue(mCtx.getApplicationContext());
}
return mRequestQueue;
}
public <T> void addToRequestQueue(Request<T> request){
getRequestQueue().add(request);
}
public ImageLoader getmImageLoader(){
return mImageLoader;
}
}
............................................... ........ ThugAdapter.java
................................................................... ThugAdapter.java
package com.example.osama.recyclerthug;
import android.net.Uri;
import android.support.annotation.NonNull;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;
import java.util.ArrayList;
public class ThugAdapter extends RecyclerView.Adapter<ThugAdapter.ThugHolder> {
ArrayList<Info> arrayList1;
public ThugAdapter(ArrayList<Info> arrayList){
this.arrayList1 = arrayList;
}
@NonNull
@Override
public ThugHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
LayoutInflater inflater = LayoutInflater.from(viewGroup.getContext());
View view = inflater.inflate(R.layout.appearance, viewGroup, false);
ThugHolder thugHolder = new ThugHolder(view);
return thugHolder;
}
@Override
public void onBindViewHolder(@NonNull ThugHolder thugHolder, int i) {
thugHolder.text.setText(arrayList1.get(i).getTxt1());
thugHolder.text2.setText(arrayList1.get(i).getTxt2());
/* thugHolder.image.setImageURI(arrayList.get(i).getImageUri());*/
}
@Override
public int getItemCount() {
return arrayList1.size();
}
public class ThugHolder extends RecyclerView.ViewHolder{
TextView text,text2;
ImageView image;
public ThugHolder(@NonNull View itemView) {
super(itemView);
text = itemView.findViewById(R.id.textView);
text2 = itemView.findViewById(R.id.textView2);
image = itemView.findViewById(R.id.imageView);
}
}
}
............................................... ............................. Info.java
............................................................................ Info.java
package com.example.osama.recyclerthug;
import android.net.Uri;
public class Info {
private String txt1,txt2;
// private Uri imageuri;
public Info(String txt1, String txt2/*, Uri imageuri*/){
this.setTxt1(txt1);
this.setTxt2(txt2);
/* this.setImageUri(imageuri);*/
}
public String getTxt1() {
return txt1;
}
public void setTxt1(String txt1) {
this.txt1 = txt1;
}
public String getTxt2() {
return txt2;
}
public void setTxt2(String txt2) {
this.txt2 = txt2;
}
/*public Uri getImageUri() {
return imageuri;
}
public void setImageUri(Uri imageuri) {
this.imageuri = imageuri;
}*/
}
............................................... ...... BackgroundTask.java
........................................................ BackgroundTask.java
package com.example.osama.recyclerthug;
import android.content.Context;
import android.net.Uri;
import android.util.Log;
import android.widget.Toast;
import com.android.volley.Request;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.JsonArrayRequest;
import com.android.volley.toolbox.JsonObjectRequest;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
public class BackgroundTask {
Context context;
ArrayList<Info> arrayList;
String json_url = "http://cc97cf60.ngrok.io/api/note/";
public BackgroundTask(Context context){
this.context = context;
}
public ArrayList<Info> getArrayList(){
arrayList = new ArrayList<>();
JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(Request.Method.GET, json_url, null,
new Response.Listener<JSONObject>() {
@Override
public void onResponse(JSONObject response) {
JSONArray jsonArray ;
try {
jsonArray = response.getJSONArray("objects");
int i;
for (i = 0; i < jsonArray.length(); i++){
JSONObject jsonObject = (JSONObject) jsonArray.get(i);
/* Uri b = Uri.parse(jsonObject.getString("image")); //Type casting string to uri*/
String a = jsonObject.getString("title");
String b = jsonObject.getString("body");
Info info = new Info(a,b);
arrayList.add(info);
}
} catch (JSONException e) {
e.printStackTrace();
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
}
});
Singleton.getInstance(context).addToRequestQueue(jsonObjectRequest);
return arrayList;
}
}
................................................... MainActivity.java
.............................................. MainActivity.java
package com.example.osama.recyclerthug;
import android.app.DownloadManager;
import android.net.Uri;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import com.android.volley.Request;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.JsonObjectRequest;
import org.json.JSONObject;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity {
RecyclerView recyclerView;
RecyclerView.LayoutManager layoutManager;
ThugAdapter thugAdapter;
BackgroundTask backgroundTask;
ArrayList<Info> arrayList;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
recyclerView = findViewById(R.id.recycler);
layoutManager = new LinearLayoutManager(this);
recyclerView.setLayoutManager(layoutManager);
recyclerView.setHasFixedSize(true);
backgroundTask = new BackgroundTask(this);
arrayList = new ArrayList<>();
arrayList= backgroundTask.getArrayList();
thugAdapter = new ThugAdapter(arrayList);
recyclerView.setAdapter(thugAdapter);
}
}
以下是json数据:
Below is the json data:
{
"meta": {
"limit": 20,
"next": null,
"offset": 0,
"previous": null,
"total_count": 2
},
"objects": [
{
"body": "Breaking News:\r\nOsama Abrar is Iron Man.",
"created_at": "2018-12-08T08:40:59.949776",
"id": 1,
"image": "https://wonderfulengineering.com/wp-content/uploads/2016/01/iron-man-wallpaper-6.jpg",
"resource_uri": "/api/note/1/",
"title": "Iron Man"
},
{
"body": "Will Iron Man aka Osama Abrar survive?",
"created_at": "2018-12-08T08:41:40.279677",
"id": 2,
"image": "https://marciokenobi.files.wordpress.com/2013/03/iron_man.jpg",
"resource_uri": "/api/note/2/",
"title": "End Game"
}
]
}
推荐答案
JSON解析是可以的，但是您不能像这样检索数据，因为您在异步模式下使用了Volley.这意味着您不能假设将请求放入队列后就可以检索到数据.也许队列很长，您的请求可以稍后发送.因此，当您尝试检索数据时，您已经发现arrayList为null，这是正常的.为了处理异步方式，您必须告诉Volley:在检索数据时告诉我".您可以使用侦听器来做到这一点.
JSON parsing is OK but you can't retrieve your data like this because you used Volley in asynchronous mode. It means that you can't assume that data will be retrieved as soon as you put the request in the queue. Maybe the queue is very long and your request can be sent later. So, when you tried to retrieve your data, you've seen that your arrayList is null, and it's normal. To deal with the asynchronous way, you have to tell Volley : "tell me when you've retrieved data". And you can do this with a listener.
这里是一个例子.
public interface Listener {
void onDataReceived(ArrayList<Info> list);
void onError(int error);
}
BackgroundTask
public class BackgroundTask {
Context context;
ArrayList<Info> arrayList;
Listener mListener; // listener to retrieve data
String json_url = "http://cc97cf60.ngrok.io/api/note/";
public BackgroundTask(Context context, Listener listener) {
this.context = context;
mListener = listener;
}
public void getArrayList() { // no return needed
arrayList = new ArrayList<>();
JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(Request.Method.GET, json_url, null,
new Response.Listener<JSONObject>() {
@Override
public void onResponse(JSONObject response) {
JSONArray jsonArray;
try {
jsonArray = response.getJSONArray("objects");
int i;
for (i = 0; i < jsonArray.length(); i++) {
JSONObject jsonObject = (JSONObject) jsonArray.get(i);
/* Uri b = Uri.parse(jsonObject.getString("image")); //Type casting string to uri*/
String a = jsonObject.getString("title");
String b = jsonObject.getString("body");
Info info = new Info(a, b);
arrayList.add(info);
}
} catch (JSONException e) {
e.printStackTrace();
}
// if listener has been set, send data
if (mListener != null) {
mListener.onDataReceived(arrayList);
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
// if listener has been set, send error
if (mListener != null) {
mListener.onError(error.networkResponse.statusCode);
}
}
});
Singleton.getInstance(context).addToRequestQueue(jsonObjectRequest);
}
}
在您的 MainActivity 中:
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
recyclerView = findViewById(R.id.recycler);
layoutManager = new LinearLayoutManager(this);
recyclerView.setLayoutManager(layoutManager);
recyclerView.setHasFixedSize(true);
backgroundTask = new BackgroundTask(this, new Listener() {
@Override
public void onDataReceived(ArrayList<Info> list) {
thugAdapter = new ThugAdapter(list);
recyclerView.setAdapter(thugAdapter);
}
@Override
public void onError(int error) {
}
});
backgroundTask.getArrayList();
}
那就是！
这篇关于无法显示Json数据的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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