显示错误:尝试在空对象引用上调用接口方法'int java.util.List.size()' [英] Showing Error :Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
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问题描述
我正在创建一个在列表视图中显示联系人列表的应用程序.问题是我在运行应用程序时遇到以下错误,并且正在努力解决该问题:
I'm creating an app that display contact list in a listview.The problem is I'm getting the following error when I run my app and I'm struggling to fix it:
04-05 13:41:48.868 2488-2488/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.kksworld.jsonparsing, PID: 2488
java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
at android.widget.ArrayAdapter.getCount(ArrayAdapter.java:337)
at android.widget.ListView.setAdapter(ListView.java:491)
at com.kksworld.jsonparsing.MainActivity$JSONTask.onPostExecute(MainActivity.java:120)
at com.kksworld.jsonparsing.MainActivity$JSONTask.onPostExecute(MainActivity.java:48)
at android.os.AsyncTask.finish(AsyncTask.java:651)
at android.os.AsyncTask.-wrap1(AsyncTask.java)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:668)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
这是我的代码:
MainActivity.java
package com.kksworld.jsonparsing;
import android.content.Context;
import android.os.AsyncTask;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;
import com.kksworld.jsonparsing.models.ContactModel;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends AppCompatActivity {
private ListView listView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
listView = (ListView)findViewById(R.id.lvContacts)
}
public class JSONTask extends AsyncTask<String,String,List<ContactModel>>{
@Override
protected List<ContactModel> doInBackground(String... params) {
HttpURLConnection httpURLConnection = null;
BufferedReader bufferedReader = null;
try {
URL url = new URL(params[0]);
httpURLConnection = (HttpURLConnection) url.openConnection();
httpURLConnection.connect();
InputStream inputStream = httpURLConnection.getInputStream();
// Through this we can read the data line by line
bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
StringBuffer stringBuffer = new StringBuffer();
String line = "";
while ((line = bufferedReader.readLine()) != null) {
stringBuffer.append(line);
}
String finalJSON = stringBuffer.toString();
JSONArray mainArray = new JSONArray(finalJSON);
JSONObject parentObject = mainArray.getJSONObject(0);
JSONArray parentArray = parentObject.getJSONArray("contacts");
List<ContactModel> contactModelList = new ArrayList<>();
// For parsing a list of items you have to use for loop
for(int i=0;i<11;i++) {
JSONObject finalObject = parentArray.getJSONObject(i);
ContactModel contactModel = new ContactModel();
contactModel.setName(finalObject.getString("name"));
contactModel.setPhone(finalObject.getString("phone"));
contactModel.setEmail(finalObject.getString(("email")));
contactModel.setOfficePhone(finalObject.getString(("officePhone")));
contactModel.setLatitude((float) finalObject.getDouble("latitude"));
contactModel.setLongitude((float) finalObject.getDouble("longitude"));
// Adding the finalObject in the List
contactModelList.add(contactModel);
}
return contactModelList;
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (JSONException e) {
e.printStackTrace();
} finally {
if (httpURLConnection != null) {
httpURLConnection.disconnect();
try {
if (bufferedReader != null) {
bufferedReader.close();
}
}catch(IOException e){
e.printStackTrace();
}
}
}
return null;
}
// Value returned by doInBackGround will be passed here...
@Override
protected void onPostExecute(List<ContactModel> result) {
super.onPostExecute(result);
ContactAdapter contactAdapter = new ContactAdapter(getApplicationContext(),R.layout.row,result);
listView.setAdapter(contactAdapter);
}
}
public class ContactAdapter extends ArrayAdapter{
private List<ContactModel> contactModelList;
private int resource;
private LayoutInflater inflater;
public ContactAdapter(Context context, int resource, List<ContactModel> objects) {
super(context, resource, objects);
contactModelList=objects;
this.resource=resource;
inflater = (LayoutInflater) getSystemService(LAYOUT_INFLATER_SERVICE);
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if(convertView == null)
{
convertView = inflater.inflate(resource,null);
}
TextView textViewName;
TextView textViewEmail;
TextView textViewPhone;
TextView textViewOfficePhone;
textViewName = (TextView)convertView.findViewById(R.id.textViewInsertName);
textViewEmail= (TextView)convertView.findViewById(R.id.textViewInsertEmail);
textViewPhone= (TextView)convertView.findViewById(R.id.textViewInsertPhone);
textViewOfficePhone = (TextView)convertView.findViewById(R.id.textViewInsertOfficeNumber);
textViewName.setText(contactModelList.get(position).getName());
textViewEmail.setText(contactModelList.get(position).getEmail());
textViewPhone.setText(contactModelList.get(position).getPhone());
textViewOfficePhone.setText(contactModelList.get(position).getOfficePhone());
return convertView;
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_refresh) {
new JSONTask().execute("some_url");
return true;
}
return super.onOptionsItemSelected(item);
}
}
有人可以帮忙吗?
推荐答案
提取此行
List<ContactModel> contactModelList = new ArrayList<>();
在try块之前,使用return contactModelList;
before the try block and instead of return null;
use return contactModelList;
看起来解析失败,您将null
对象传递给onPostExecute()
.
Looks like your parsing fails and you pass a null
object to onPostExecute()
.
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