Question

我正在尝试解析JSON提要并将其显示到自定义列表视图中，但我收到了NullPointerException。这里是我正在使用的代码，我使用了volley并解析了响应，它在一个简单的列表视图上正常工作，但是自定义列表视图存在问题。请任何人解决这个问题，将不胜感激。

public class News extends Activity {
    ListView lv;
    Context context;
    String uri = "http://lodhisamaj.16mb.com/jsongen.php";
    String[] newstitle;
    String[] newsdesc;

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    context = this;
    setContentView(R.layout.news);
    lv = (ListView) findViewById(R.id.newslist);
    Myadapter adapter = new Myadapter(this, newstitle, newsdesc);
    lv.setAdapter(adapter);
    RequestQueue rq = Volley.newRequestQueue(this);
    JsonObjectRequest jreq = new JsonObjectRequest(
            com.android.volley.Request.Method.GET, uri, null,
            new Response.Listener<JSONObject>() {
                @Override
                public void onResponse(JSONObject response) {
                    try {
                        JSONArray title = response.getJSONArray("data");

                        for (int i = 0; i < title.length(); i++) {
                            String xy = title.getJSONObject(i).getString(
                                    "Title");
                            String xy2 = title.getJSONObject(i).getString(
                                    "Meassage");
                            xy = newstitle[i];
                            xy2 = newsdesc[i];
                        }

                    } catch (JSONException e) {

                    }
                }
            }, new Response.ErrorListener() {

                @Override
                public void onErrorResponse(VolleyError error) {
                    Toast.makeText(context, error.toString(),
                            Toast.LENGTH_LONG).show();
                }
            });
    rq.add(jreq);
}}             


class Myadapter extends ArrayAdapter<String> {
    Context context;
    String[] titleArray;
    String[] descArray;

public Myadapter(Context c, String[] newstitle, String[] newsdesc) {
    super(c, R.layout.news_row, newstitle);
    this.context = c;
    this.titleArray = newstitle;
    this.descArray = newsdesc;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    LayoutInflater inflator = (LayoutInflater) context
            .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    View row = inflator.inflate(R.layout.news_row, parent, false);
    TextView myTitle = (TextView) row.findViewById(R.id.newstitle);
    TextView mydec = (TextView) row.findViewById(R.id.newsdec);
    myTitle.setText(titleArray[position]);
    mydec.setText(descArray[position]);
    return row;
}}

Answer 1

假设其他一切正常，您可以通过将String[]切换为ArrayList<String>来纠正NullPointerException（和IndexOutOfBoundsException）。

问题是这两行没有初始化String[]，所以它们将为null。

String[] newstitle;
String[] newsdesc;

此外，不确定这两行有意做什么......

xy = newstitle[i];
xy2 = newsdesc[i];

话虽如此，希望这对你有用。（未测试）

public class News extends Activity {
    ListView lv;
    Context context;
    String uri = "http://lodhisamaj.16mb.com/jsongen.php";
    ArrayList<String> newstitle;
    ArrayList<String> newsdesc;

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    context = this;
    setContentView(R.layout.news);

    // Initialize your lists so they are not null
    newstitle = new ArrayList<String>();
    newsdesc = new ArrayList<String>();

    lv = (ListView) findViewById(R.id.newslist);
    Myadapter adapter = new Myadapter(this, newstitle, newsdesc);
    lv.setAdapter(adapter);
    RequestQueue rq = Volley.newRequestQueue(this);
    JsonObjectRequest jreq = new JsonObjectRequest(
            com.android.volley.Request.Method.GET, uri, null,
            new Response.Listener<JSONObject>() {
                @Override
                public void onResponse(JSONObject response) {
                    try {
                        JSONArray title = response.getJSONArray("data");

                        for (int i = 0; i < title.length(); i++) {
                            String xy = title.getJSONObject(i).getString(
                                    "Title");
                            String xy2 = title.getJSONObject(i).getString(
                                    "Meassage");

                            // Add your strings to your lists
                            newstitle.add(xy);
                            newsdesc.add(xy2);
                        }

                    } catch (JSONException e) {
                         e.printStackTrace(); // never ignore your errors
                    }
                }
            }, new Response.ErrorListener() {

                @Override
                public void onErrorResponse(VolleyError error) {
                    Toast.makeText(context, error.toString(),
                            Toast.LENGTH_LONG).show();
                }
            });
    rq.add(jreq);
}}             


class Myadapter extends ArrayAdapter<String> {
    Context context;
    ArrayList<String> titleArray;
    ArrayList<String> descArray;

public Myadapter(Context c, ArrayList<String> newstitle, ArrayList<String> newsdesc) {
    super(c, R.layout.news_row, newstitle);
    this.context = c;
    this.titleArray = newstitle;
    this.descArray = newsdesc;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    LayoutInflater inflator = (LayoutInflater) context
            .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    View row = inflator.inflate(R.layout.news_row, parent, false);
    TextView myTitle = (TextView) row.findViewById(R.id.newstitle);
    TextView mydec = (TextView) row.findViewById(R.id.newsdec);
    myTitle.setText(titleArray.get(position));
    mydec.setText(descArray.get(position));
    return row;
}}

我试图解析JSON提要并将其显示到自定义列表视图，但我得到NullPointerException

1 个答案: