解析 Json 数据并将其膨胀到 ListView

Question

大家好，我正在尝试解析 Json 数据并尝试将其显示到 ListView 中。自过去 8 小时以来一直在尝试此操作，但未能成功。基本上我不想为不同的值（JSONObjects）使用不同的 ArrayList。我想将值存储在对象中，并且使用数据模型并将该模型中的值获取到自定义 ArrayAdapter 中并将其膨胀到 ListView 中。

现在的问题：列表中没有显示任何内容。只是一个空白活动。

下面是我的代码。我没有粘贴 XML，因为这是非常简单的 ListView 和 1 个带有图像和 2 个文本视图的 list_item。

Volley3.Java

package com.droidacid.networkingdemo.http_using_volley;

import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.widget.ListView;
import com.android.volley.Request;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.JsonObjectRequest;
import com.droidacid.networkingdemo.L;
import com.droidacid.networkingdemo.R;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;


public class Volley3 extends Activity {

ListView lvVolley3;
//ArrayList<Volley3DataModel> videoArray = new ArrayList<Volley3DataModel>();
Volley3ListAdapter videoAdapter;
Volley3DataModel dataModel;
String feedUrl = "https://gdata.youtube.com/feeds/api/users/slidenerd/uploads?v=2&alt=jsonc&start-index=1&max-results=10";
Context context = this;
String videoTitle, videoUploadedAt, videoThumbnailURL;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.volley3);
    lvVolley3 = (ListView) findViewById(R.id.lvVolley3);


    callJson();
    lvVolley3.setAdapter(videoAdapter);
}

private void callJson() {
    JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(Request.Method.GET, feedUrl, null,
            new Response.Listener<JSONObject>() {
                @Override
                public void onResponse(JSONObject jsonObject) {
                    // We perform all the JSON operations in this method.
                    try {
                        // This gets a JsonArray which is inside a JsonObject
                        JSONArray jsonVideoArray = jsonObject.getJSONObject("data").getJSONArray("items");

                        for(int i = 0; i < jsonVideoArray.length(); i++) {
                            JSONObject jsonItems = jsonVideoArray.getJSONObject(i);
                            videoTitle = jsonItems.getString("title");

                            videoThumbnailURL = jsonItems.getJSONObject("thumbnail").getString("sqDefault");
                            videoUploadedAt = jsonItems.getString("uploaded");
                            //L.l("Titles : " + videoTitle + ". Url :  " + videoThumbnailURL + " Uploaded At : " + videoUploadedAt);
                            dataModel = new Volley3DataModel(videoTitle, videoThumbnailURL, videoUploadedAt);
                            //videoArray.add(dataModel);
                        }
                    } catch (JSONException e) {
                        L.l("I am a Json Exception : " + e.toString());
                    }
                }
            },
            new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError volleyError) {
                    L.l("Error happened hoooo : " + volleyError.toString());
                    L.t(context, "Error happened hoooo : " + volleyError.toString());
                }
            }
    );

    videoAdapter = new Volley3ListAdapter(this, dataModel);
    //Tell the videoAdapter that the List Data has been changed
    //Telling the Adapter that the data has been changed

    L.l("DataSet changing");
    videoAdapter.notifyDataSetChanged();
    VolleyApplication.getInstance().getRequestQueue().add(jsonObjectRequest);
}
}

Volley3DataModel.java

package com.droidacid.networkingdemo.http_using_volley;


public class Volley3DataModel {
private String title, url, updated;

Volley3DataModel(String title, String url, String updated) {
    this.title = title;
    this.url = url;
    this.updated = updated;
}

public String getTitle() {
    return title;
}

public String getUrl() {
    return url;
}

public String getUpdated() {
    return updated;
}
}

Volley3ListAdapter.java

package com.droidacid.networkingdemo.http_using_volley;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;

import com.droidacid.networkingdemo.L;
import com.droidacid.networkingdemo.R;
import com.squareup.picasso.Picasso;


public class Volley3ListAdapter extends ArrayAdapter<Volley3DataModel> {
ImageView ivThumb;
Volley3DataModel myData;
TextView tvTitle, tvUploaded;
Context context;
String title, url, uploaded;
//ArrayList<Volley3DataModel> myDataList;
public Volley3ListAdapter(Context context, Volley3DataModel dataModel) {
    super(context, R.layout.volley3_list_youtube_item);
    L.l("Volley3ListAdapter() constructor");
    this.context = context;
    this.myData = dataModel;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    L.l("I'm inside getView()");
    if(convertView == null) {
        L.l("ConvertView is null so inflating the convertView");
        //convertView = LayoutInflater.from(context).inflate(R.layout.volley3_list_youtube_item, parent, false);
        LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        convertView = inflater.inflate(R.layout.volley3_list_youtube_item, parent, false);
    }
    L.l("Assigning values to the views");
    ivThumb = (ImageView) convertView.findViewById(R.id.ivVolley3);
    tvTitle = (TextView) convertView.findViewById(R.id.tvTitleVolley3);
    tvUploaded = (TextView) convertView.findViewById(R.id.tvUploadedVolley3);


    L.l("Loading the data into the Views");
    Picasso.with(getContext()).load(myData.getUrl()).centerCrop().into(ivThumb);
    tvTitle.setText(myData.getTitle());
    tvUploaded.setText(myData.getUpdated());
    return convertView;
}
}

我知道有很多帖子与使用 JSON 将数据显示到 ListView 相关，但我的问题是将包含所有 3 个字符串值的对象传递到 ArrayLisy 或将值传递到模型并从那里获取值。只是想提高我使用模型、泛型和单个对象的技能。

提前致谢

Answer 1

将这些行移到 try 块的末尾。

原因：当dataModel 中没有数据时，您正在尝试创建适配器。网络调用返回json后才可用。

videoAdapter = new Volley3ListAdapter(this, dataModel);
//Tell the videoAdapter that the List Data has been changed
//Telling the Adapter that the data has been changed

L.l("DataSet changing");
videoAdapter.notifyDataSetChanged();

P.S. 您的代码的编写方式只会显示一项。您需要使用模型数组并将其传递给适配器。在适配器的getView 方法中使用位置变量来获取要在列表视图中呈现的正确值。