将来自 JSON 响应的数据放入适配器 (ListView) 时出错

Question

最近学习了ListView的使用，所以不是很熟练。我在将来自 JSON 响应的数据添加到 ListView 时遇到问题。当我将硬编码字符串添加到 ListView 时，它工作正常。但是在从 JSON 响应中放入数据时什么也不提供。这是我的 activity (SupportedAds.java)

public class SupportedAds extends AppCompatActivity {

String[] Title;
String[] Content;
ListView list;
Offers offer;
ArrayList<Offers> offers = new ArrayList<>();

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_supported_ads);
    list = findViewById(R.id.list);


/* Getting Supported Ads from the api*/
    RequestQueue queue = Volley.newRequestQueue(SupportedAds.this);
    final String URL_SUPPORTED_ADS = "http://lb-89089438.us-east-2.elb.amazonaws.com/api/offers";

    StringRequest postRequest = new StringRequest(Request.Method.POST, URL_SUPPORTED_ADS,
            new Response.Listener<String>()
            {
                @Override
                public void onResponse(String response) {
                    JSONArray jsonResponse;
                    String offerContent;
                    String offerTitle;
                    // response
                    Log.wtf("POST api/offers", response);
                    try {
                        jsonResponse = new JSONArray(response);
                        Title = new String[jsonResponse.length()];
                        Content = new String[jsonResponse.length()];

                        for(int i=0; i < jsonResponse.length(); i++)
                        {
                            JSONObject jsonobject = jsonResponse.getJSONObject(i);
                            offerContent  = jsonobject.getString("offercontent");
                            offerTitle = jsonobject.getString("offertitle");

                            offer = new Offers();
                            offer.setTitle(offerTitle);
                            offer.setContent(offerContent);
                            Log.e("Title", offerTitle); // shows correct values. No problem in JSON parsing or POST request
                            Log.e("Content", offerContent); // shows correct values. No problem in JSON parsing or POST request
                            offers.add(offer);
                        }

                    } catch (JSONException e) {
                        e.printStackTrace();
                    }
                }
            },
            new Response.ErrorListener()
            {
                @Override
                public void onErrorResponse(VolleyError error) {
                    // error
                    Log.d("POST api/offers", error.toString());
                }
            }
    ) {
        @Override
        protected Map<String, String> getParams()
        {
            return new HashMap<>();
        }
    };
    queue.add(postRequest);
/* Getting Supported Ads from the api*/

    /* If i use these hard coded values, it works fine */
    /*offer = new Offers();
    offer.setTitle("Ad1");
    offer.setContent("Advertisement #01 Description");
    offers.add(offer);

    offer = new Offers();
    offer.setTitle("Ad2");
    offer.setContent("Advertisement #02 Description");
    offers.add(offer);

    offer = new Offers();
    offer.setTitle("Ad3");
    offer.setContent("Advertisement #03 Description");
    offers.add(offer);*/

    list.setAdapter(new MyAdapter(getApplicationContext(), offers));

}

private class MyAdapter extends BaseAdapter {

    private Context context;
    private ArrayList<Offers> offers;

    public MyAdapter(Context context, ArrayList<Offers> offers) {
        this.context = context;
        this.offers = offers;
    }

    @Override
    public int getCount() {
        return offers.size();
    }

    @Override
    public Object getItem(int position) {
        return offers.get(position);
    }

    @Override
    public long getItemId(int position) {
        return 0;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        TwoLineListItem twoLineListItem;

        if (convertView == null) {
            LayoutInflater inflater = (LayoutInflater) context
                    .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            twoLineListItem = (TwoLineListItem) inflater.inflate(
                    android.R.layout.simple_list_item_2, null);
        } else {
            twoLineListItem = (TwoLineListItem) convertView;
        }

        TextView text1 = twoLineListItem.getText1();
        TextView text2 = twoLineListItem.getText2();

        text1.setText(offers.get(position).getTitle());
        text2.setText(offers.get(position).getContent());

        return twoLineListItem;
    }
}
}

当我尝试使用来自 JSON 响应的数据时（未显示任何数据 - 抱歉背景颜色）

当我使用硬编码字符串时（在这种情况下工作正常 - 抱歉背景颜色）

布局文件（activity_supported_ads.xml）

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:background="@color/lightgreen"
tools:context="com.fyp.mrisecondscreen.activity.SupportedAds">

<ListView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/list">

</ListView>

</RelativeLayout>

来自 POST 请求的响应（我确信我在 JSON 响应解析中没有问题，因为我使用 Log.e 来显示提取的值并且它们是正确的）

[
{
"offercontent": "Sample Description",
"offertitle": "Ad 1",

},
{
"offercontent": "42 inch TV",
"offertitle": "TV ",

},
{
"offercontent": "Coke Ad Offer description here",
"offertitle": "Coke",

},
{
"offercontent": "Cola Ad Offer description here",
"offertitle": "Cola Offer",

},
{
"offercontent": "Nestle Ad Offer description here",
"offertitle": "Nestle Cerelac Offer",
},
{
"offercontent": "New Year sale",
"offertitle": "Chocolate",

}
]

请帮帮我，我花了很多时间无法解决..

Answer 1

您的代码 list.setAdapter(new MyAdapter(getApplicationContext(), offers)); 在请求完成之前执行，因此没有数据可显示。此行应在 onResponse 方法内完成解析后执行。

将来自 JSON 响应的数据放入适配器 (ListView) 时出错

Error putting data from JSON response into Adapter (ListView)

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