Question

我正在使用异步任务将json检索到baseadapter并最终将其显示到listview中。我无法做到这一点，我得到错误，我的应用程序崩溃。这是我的代码： MainActivity.java

    private String jsonString, url, username;
JSONArray JArray;
ImageView profileimg;
ListView lv;
BaseAdapterTest adapter;
private JSONArray questions;
JSONObject temp_obj;
ArrayList<String> test = new ArrayList<String>();
public static String Tag_profile_pic = "profile_pic";
public static String Tag_username = "username";

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.nnj);
    lv = (ListView) findViewById(R.id.listview);
           new GetJson().execute();


}

;

private class GetJson extends AsyncTask<Void, Void, Void> {
    @Override
    protected void onPreExecute() {
        super.onPreExecute();

    }


    @Override
    protected Void doInBackground(Void... params) {
        ServiceHandler http = new ServiceHandler();
        jsonString = http.makeServiceCall(url, ServiceHandler.GET,
                null);
        if (jsonString != null) {
            try {

                // Getting JSON Array node
                JArray = new JSONArray(jsonString);

                // looping through All Contacts
                for (int i = 0; i < JArray.length(); i++) {
                    temp_obj = JArray.getJSONObject(i);
                    JSONObject currentObject = new JSONObject();
                    currentObject.put("profile_pic", temp_obj.getString(Tag_profile_pic)
                            .toString());
                    currentObject.put("username", temp_obj.getString(Tag_username)
                            .toString());
                    JArray.put(currentObject);
                }

            } catch (JSONException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        } else {
            Log.d("TAG", "Empty");
        }
        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        // TODO Auto-generated method stub
        super.onPostExecute(result);
        Toast.makeText(getApplicationContext(), JArray + "", Toast.LENGTH_LONG).show();
        adapter = new BaseAdapterTest(MainActivity.this, JArray) {
            @Override
            public int getCount() {
                return 0;
            }

            @Override
            public Object getItem(int position) {
                return null;
            }

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

            @Override
            public View getView(int position, View convertView, ViewGroup parent) {
                return null;
            }
        };
        // Set the adapter to the ListView
        lv.setAdapter(adapter);
    }


}

}

和BaseAdapter.java的代码

public class BaseAdapterTest extends android.widget.BaseAdapter {

// Declare Variables
Context context;
LayoutInflater inflater;
Array JArray;


public BaseAdapterTest(MainActivity mainActivity, JSONArray JArray) {
}

@Override
public int getCount() {
    return getCount();
}

@Override
public Object getItem(int position) {
    return null;
}

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

public View getView(final int position, View convertView, ViewGroup parent) {
    // Declare Variables
    TextView username;
    ImageView profilepic;

    inflater = (LayoutInflater) context
            .getSystemService(Context.LAYOUT_INFLATER_SERVICE);

    View itemView = inflater.inflate(R.layout.listview, parent, false);
    // Locate the TextViews in listview_item.xml
    username = (TextView) itemView.findViewById(R.id.questionfeed_customelistview_txt_username);

    // Locate the ImageView in listview_item.xml
    profilepic = (ImageView) itemView.findViewById(R.id.questionfeed_customelistview_imgv_follow);

    itemView.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View arg0) {
            // Get the position
            Intent intent = new Intent(context, MainActivity.class);
            // Pass all data rank
            intent.putExtra("username", (MainActivity.Tag_username));
            // Pass all data flag
            intent.putExtra("profilepic",(MainActivity.Tag_profile_pic));
            // Start SingleItemView Class
            context.startActivity(intent);

        }
    });
    return itemView;
}

}

这是我的Logcat

04-02 15:49:31.871    2935-2935/com.cheerz.json E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.cheerz.json, PID: 2935
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
        at com.cheerz.json.MainActivity$GetJson.onPostExecute(MainActivity.java:115)
        at com.cheerz.json.MainActivity$GetJson.onPostExecute(MainActivity.java:47)
        at android.os.AsyncTask.finish(AsyncTask.java:632)
        at android.os.AsyncTask.access$600(AsyncTask.java:177)
        at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5312)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)

Answer 1

替换

JArray = new JSONArray(jsonString);

与

 JSONObject jsonobject = new JSONObject(jsonString);
 JArray = ((JSONObject) jsonobject).getJSONArray("key_name_of_your_array");

无法检索Json

1 个答案: