我刚刚发布了昨天，但现在我试图获取我的数据并将其放入ListView而不是TextView。应用程序在显示listview活动后崩溃。如果有人对此有任何线索，将非常感谢帮助。
继承活动代码：
package com.example.Accomplist;
import android.app.Activity;
import android.app.ListActivity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.RemoteException;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpUriRequest;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.util.EntityUtils;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.IOException;
/**
* Created with IntelliJ IDEA.
* User: DESAI_628IL
* Date: 3/1/13
* Time: 7:34 PM
* To change this template use File | Settings | File Templates.
*/
public class MainScreen extends ListActivity{
JSONObject jsonObj= null;
String[] eventArr= new String[10];
int i=0;
// HttpClient client;
// url to make request
String[] urlArr = new String[10];//"http://accomplist.herokuapp.com/api/v1/sharedevent/1/?format=json";
//Following comment block is example of json object from above url
{
/*
{
"date":"2013-01-17T12:48:24.326859",
"event":{
"description":"I want to find work that I love so that I never have to work a day in my life.",
"id":3,
"resource_uri":"/api/v1/event/3/",
"title":{
"id":3,
"listitem":"Get a Job I Enjoy",
"resource_uri":"/api/v1/title/3/"
},
"user":{
"date_joined":"2013-01-17T12:40:17.115755",
"email":"sourabhdesai@gmail.com",
"first_name":"",
"id":3,
"is_active":true,
"is_staff":false,
"is_superuser":false,
"last_login":"2013-02-02T15:51:11.622505",
"last_name":"",
"password":"pbkdf2_sha256$10000$ETuiYJXQjvez$5yHd5IPaQpS0SvlissO/JydwXUHhMYDgadY7uyTyWg0=",
"resource_uri":"/api/v1/user/3/",
"username":"sourabhd"
}
},
"id":2,
"resource_uri":"/api/v1/sharedevent/2/",
"votes":7
}
*/
}
private static final String TAG_EVENT="event"; //A JSON object within the JSON object that will be returned by JSONParse()
private static final String TAG_DESCRIPTION="description"; //A JSON tag within the JSON object EVENT
private static String eventString="Yo";
protected void onCreate(Bundle savedInstanceState) {
for(int b=0; b<urlArr.length; b++) {
urlArr[b]= "http://accomplist.herokuapp.com/api/v1/sharedevent/"+(b+1)+"/?format=json";
}
super.onCreate(savedInstanceState);
setContentView(R.layout.main_screen);
ListView eventsList= getListView();
new JSONParse().execute(urlArr[0],urlArr[1],urlArr[2],urlArr[3],urlArr[4],urlArr[5],urlArr[6],urlArr[7],urlArr[8]);
}
private class JSONParse extends AsyncTask<String, Void, String> {
HttpClient client=new DefaultHttpClient();
@Override
protected String doInBackground(String... jsonurl) {
// StringBuilder url= new StringBuilder(String.valueOf(jsonurl));
HttpUriRequest request= new HttpGet("http://accomplist.herokuapp.com/api/v1/sharedevent/2/?format=json");
HttpResponse r= null;
try {
r = client.execute(request);
} catch (ClientProtocolException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
} catch (IOException e) {
e.printStackTrace(); //To change body of catch statement use File | Settings | File Templates.
}
int status= r.getStatusLine().getStatusCode();
if (status==200){
HttpEntity e=r.getEntity();
String data= null;
try {
data = EntityUtils.toString(e);
} catch (IOException e1) {
e1.printStackTrace(); //To change body of catch statement use File | Settings | File Templates.
}
try {
jsonObj = new JSONObject(data);
} catch (JSONException e1) {
e1.printStackTrace(); //To change body of catch statement use File | Settings | File Templates.
}
try {
JSONObject eventJson= jsonObj.getJSONObject(TAG_EVENT);
eventString= eventJson.getString(TAG_DESCRIPTION);
}
catch (JSONException e1) {
eventString="Couldn't Parse Data";
}
return eventString;
}
else{
return eventString;
}
}
protected void onProgressUpdate() {
Toast loadingToast= Toast.makeText(getApplicationContext(), "Loading", Toast.LENGTH_LONG);
loadingToast.show();
}
protected void onPostExecute(String result) {
eventString=result;
eventArr[i]=eventString;
i++;
MainScreen.this.setListAdapter(new ArrayAdapter<String>(MainScreen.this,
android.R.layout.simple_list_item_1,eventArr));
}
}
}
继承LogCat错误消息：
02-26 15:57:21.692: WARN/InputMethodManagerService(324): Got RemoteException sending setActive(false) notification to pid 5900 uid 10048
02-26 15:57:31.964: WARN/dalvikvm(5918): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
02-26 15:57:32.042: ERROR/AndroidRuntime(5918): FATAL EXCEPTION: main
java.lang.NullPointerException
at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:394)
at android.widget.ArrayAdapter.getView(ArrayAdapter.java:362)
at android.widget.AbsListView.obtainView(AbsListView.java:2143)
at android.widget.ListView.measureHeightOfChildren(ListView.java:1246)
at android.widget.ListView.onMeasure(ListView.java:1158)
at android.view.View.measure(View.java:15518)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4825)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
at android.view.View.measure(View.java:15518)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4825)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
at android.view.View.measure(View.java:15518)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:847)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
at android.view.View.measure(View.java:15518)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4825)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2176)
at android.view.View.measure(View.java:15518)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1874)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1089)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1265)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:989)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4351)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:749)
at android.view.Choreographer.doCallbacks(Choreographer.java:562)
at android.view.Choreographer.doFrame(Choreographer.java:532)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:735)
at android.os.Handler.handleCallback(Handler.java:725)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:5041)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
at dalvik.system.NativeStart.main(Native Method)
答案 0 :(得分：1)
首先，这一行
eventsList= getListView();
应该在onCreate()内。但是将ListView eventsList声明为字段变量，因为您只是在onCreate()
这是NPE来自ListView的来源，因为它从您Layout获得setContentView()，直到您拨打inflate或{{1}它带有inflater。因此，对getListView()的调用也需要在setContentView()
ListView
android:id="@android:id/list" Layout UI
我建议通过ListActivity Docs，因为在你理解它们之前它们可能是一件棘手的事情。我还建议观看Turbo Charge your UI，我相信我通过@Sam了解到了这一点。这个有点旧，但仍然有很多好的信息。它涉及ListView的不同部分，但提供了有关更有效地使用Caused by: java.lang.RuntimeException: Your content must have a ListView whose id attribute is 'android.R.id.list'
的良好信息。
修改
正如它在这里所说：
ListView这就是为什么我最初在我的答案中添加了这一行：）
您还需要
中android:id="@android:id/list"Layout在<ListView android:id="@android:id/list" //this is the important part android:layout_width="match_parent" android:layout_height="match_parent" android:background="#00FF00" android:layout_weight="1" android:drawSelectorOnTop="false"/>
{{1}}
答案 1 :(得分：0)
使用MainScreen上下文为ListView设置适配器，因为您在ListActivity活动中将MainScreen扩展为：
protected void onPostExecute(String result) {
eventString=result;
eventArr[i]=eventString;
i++;
MainScreen.this.setListAdapter(new ArrayAdapter<String>(MainScreen.this,
android.R.layout.simple_list_item_1,eventArr));
}