我正在尝试将JSON解析数据导入android。
我无法理解的错误是什么。
我是java和android的初学者。
这段代码并不难，你不会无聊。
我的错误和代码显示如下：
04-07 05:19:02.305: E/AndroidRuntime(19599): FATAL EXCEPTION: main
04-07 05:19:02.305: E/AndroidRuntime(19599): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.buet_parsing/com.example.buet_parsing.MainActivity}: java.lang.NullPointerException
04-07 05:19:02.305: E/AndroidRuntime(19599): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
04-07 05:19:02.305: E/AndroidRuntime(19599): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
04-07 05:19:02.305: E/AndroidRuntime(19599): at android.app.ActivityThread.access$600(ActivityThread.java:141)
04-07 05:19:02.305: E/AndroidRuntime(19599): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
04-07 05:19:02.305: E/AndroidRuntime(19599): at android.os.Handler.dispatchMessage(Handler.java:99)
04-07 05:19:02.305: E/AndroidRuntime(19599): at android.os.Looper.loop(Looper.java:137)
04-07 05:19:02.305: E/AndroidRuntime(19599): at android.app.ActivityThread.main(ActivityThread.java:5041)
04-07 05:19:02.305: E/AndroidRuntime(19599): at java.lang.reflect.Method.invokeNative(Native Method)
04-07 05:19:02.305: E/AndroidRuntime(19599): at java.lang.reflect.Method.invoke(Method.java:511)
04-07 05:19:02.305: E/AndroidRuntime(19599): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
04-07 05:19:02.305: E/AndroidRuntime(19599): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
04-07 05:19:02.305: E/AndroidRuntime(19599): at dalvik.system.NativeStart.main(Native Method)
04-07 05:19:02.305: E/AndroidRuntime(19599): Caused by: java.lang.NullPointerException
04-07 05:19:02.305: E/AndroidRuntime(19599): at android.widget.ArrayAdapter.getCount(ArrayAdapter.java:330)
04-07 05:19:02.305: E/AndroidRuntime(19599): at android.widget.ListView.setAdapter(ListView.java:462)
04-07 05:19:02.305: E/AndroidRuntime(19599): at com.example.buet_parsing.MainActivity.onCreate(MainActivity.java:46)
04-07 05:19:02.305: E/AndroidRuntime(19599): at android.app.Activity.performCreate(Activity.java:5104)
04-07 05:19:02.305: E/AndroidRuntime(19599): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
04-07 05:19:02.305: E/AndroidRuntime(19599): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
04-07 05:19:02.305: E/AndroidRuntime(19599): ... 11 more
04-07 05:19:11.135: I/Process(19599): Sending signal. PID: 19599 SIG: 9
package com.example.buet_parsing;
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;
import org.apache.http.HttpResponse;
import org.apache.http.HttpStatus;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONArray;
import org.json.JSONObject;
import org.w3c.dom.ls.LSInput;
import android.app.Activity;
import android.app.AlertDialog;
import android.app.ListActivity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.widget.Adapter;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.ProgressBar;
public class MainActivity extends Activity {
ListView lv;
CustomAdapter adapter;
String urlString="http://cricscore-api.appspot.com/csa";
ArrayList<ListIteam> allNews;
AlertDialog progressDialog;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
lv=(ListView)findViewById(R.id.list);
adapter=new CustomAdapter(this, allNews);
lv.setAdapter(adapter);
DownloadTask download=new DownloadTask();
Log.v(getClass().getSimpleName(), "Loading data.......");
AlertDialog.Builder builder=new AlertDialog.Builder(this);
builder.setMessage("Loading data..");
builder.setView(new ProgressBar(this));
progressDialog=builder.create();
progressDialog.show();
download.execute();
}
class DownloadTask extends AsyncTask<Void, Void, String>{
@Override
protected String doInBackground(Void... params) {
String result=null;
try {
HttpClient client=new DefaultHttpClient();
HttpGet get=new HttpGet(urlString);
HttpResponse response=client.execute(get);
if(response.getStatusLine().getStatusCode()==HttpStatus.SC_OK){
InputStream in=response.getEntity().getContent();
BufferedReader reader=new BufferedReader(new InputStreamReader(in));
String line=reader.readLine();
Log.v(getClass().getSimpleName(), line);
return line;
}
} catch (Exception e) {
e.printStackTrace();
return null;
}
return result;
}
@Override
protected void onPostExecute(String result) {
progressDialog.dismiss();
try {
JSONArray array=new JSONArray(result);
for (int i = 0; i < result.length(); i++) {
JSONObject object=array.getJSONObject(i);
String team1=object.getString("t1");
String team2=object.getString("t2");
ListIteam ls=new ListIteam(team1, team2);
allNews.add(ls);
adapter.notifyDataSetChanged();
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
package com.example.buet_parsing;
import java.util.ArrayList;
import java.util.List;
import android.app.Activity;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;
public class CustomAdapter extends ArrayAdapter<ListIteam>{
Activity context;
ArrayList<ListIteam> ls;
public CustomAdapter(Activity context, ArrayList<ListIteam> ls) {
super(context, R.layout.adapter_layout, ls);
this.context=context;
this.ls=ls;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View view=convertView;
LayoutInflater inflat=context.getLayoutInflater();
view=inflat.inflate(R.layout.adapter_layout, null, false);
TextView txtTeam1=(TextView)view.findViewById(R.id.team1);
TextView txtTeam2=(TextView)view.findViewById(R.id.team2);
ListIteam l=ls.get(position);
txtTeam1.setText(l.getTeam1());
txtTeam2.setText(l.getTeam2());
return view;
}
}
package com.example.buet_parsing;
public class ListIteam {
String team1;
String team2;
public ListIteam(String team1, String team2) {
super();
this.team1 = team1;
this.team2 = team2;
}
public String getTeam1() {
return team1;
}
public void setTeam1(String team1) {
this.team1 = team1;
}
public String getTeam2() {
return team2;
}
public void setTeam2(String team2) {
this.team2 = team2;
}
@Override
public String toString() {
return "ListIteam [team1=" + team1 + ", team2=" + team2 + "]";
}
}
答案 0 :(得分：1)
在展开ListActivity时，您需要一个ID为@android:id/list
你的错误堆栈也说
04-07 03:01:28.856: E/AndroidRuntime(2305): Caused by: java.lang.RuntimeException: Your content must have a ListView whose id attribute is 'android.R.id.list'
答案 1 :(得分：1)
在执行DownloadTask之前你做错了你已经设置了你的适配器，所以你总是得到NullPinterException
adapter=new CustomAdapter(this, allNews);
lv.setAdapter(adapter);
因此，您必须从onCreate()方法中移除此内容，并在onPostExecute()的{{1}}方法中进行设置。像，
DownloadTask此外，您刚刚声明了全局变量 @Override
protected void onPostExecute(String result) {
// TODO Auto-generated method stub
super.onPostExecute(result);
adapter=new CustomAdapter(this, allNews);
lv.setAdapter(adapter);
}
;没有初始化它。所以在ArrayList<ListIteam> allNews方法上初始化它。像
onCreate()答案 2 :(得分：1)
allNews为null，因此初始化allNews
替换ArrayList<ListIteam> allNews=new ArrayList<ListIteam>;