我想用json值填充listview。我能够获得所有json值，但是 我不知道问题是什么。
在我的logcat中，它显示NullPointerException，不幸的是我的活动停止了。
Suggesstion plz ......
我的java
public class Certify_Absent_List extends Activity {
private static ListView listview;
private static List<String> list;
private String teachername,date;
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
//setContentView(R.layout.);
listview=(ListView) findViewById(R.id.listView1);
list=new ArrayList<String>();
teachername=getIntent().getExtras().getString("teachername");
date=getIntent().getExtras().getString("today");
new Absent_list_bg_task().execute();
}
private class Absent_list_bg_task extends AsyncTask<String,Void,String>
{
protected String doInBackground(String... params) {
try{
String link="http://192.168.1.11:81/schoolapp/absent_list.php";
String data = URLEncoder.encode("teachername", "UTF-8")
+ "=" + URLEncoder.encode("teacher1", "UTF-8");
data += "&" + URLEncoder.encode("date", "UTF-8")
+ "=" + URLEncoder.encode("2013-01-01", "UTF-8");
/* String data = URLEncoder.encode("teachername ", "UTF-8")
+ "=" + URLEncoder.encode("teacher1", "UTF-8");
data += "&" + URLEncoder.encode("date", "UTF-8")
+ "=" + URLEncoder.encode("2013-01-01", "UTF-8");*/
URL url = new URL(link);
URLConnection conn = url.openConnection();
conn.setDoOutput(true);
OutputStreamWriter wr = new OutputStreamWriter
(conn.getOutputStream());
wr.write( data );
wr.flush();
BufferedReader reader = new BufferedReader
(new InputStreamReader(conn.getInputStream()));
StringBuilder sb = new StringBuilder();
String line = null;
// Read Server Response
while((line = reader.readLine()) != null)
{
sb.append(line);
break;
}
return sb.toString();
}catch(Exception e){
return new String("Exception: " + e.getMessage());
}
}
@Override
protected void onPostExecute(String result)
{
ArrayAdapter<String> adapter = null;
JSONArray arr = null;
JSONObject obj = null;
Toast.makeText(Certify_Absent_List.this,result, Toast.LENGTH_LONG).show();
if(result.equals("wrong"))
{
Toast.makeText(Certify_Absent_List.this,"Invalid username or password.", Toast.LENGTH_LONG).show();
}
else
{
Toast.makeText(Certify_Absent_List.this,result, Toast.LENGTH_LONG).show();
try {
arr=new JSONArray(result);
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
for(int i=0;i<arr.length();i++)
{
try {
obj=arr.getJSONObject(i);
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
try {
list.add(obj.getString("ChildName"));
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Toast.makeText(Certify_Absent_List.this,list.get(i).toString(), Toast.LENGTH_LONG).show();
}
}
adapter=new ArrayAdapter<String>(Certify_Absent_List.this, android.R.layout.simple_list_item_1, list);
//adapter.notifyDataSetChanged();
listview.setAdapter(adapter);
}
}
}
Json输出
[{"ChildName":""},{"ChildName":"childname1"},{"ChildName":"childname7"},{"ChildName":"childname11"},{"ChildName":"childname11"},{"ChildName":"childname11"}]
logcat的：
03-21 07:35:29.128: E/AndroidRuntime(1443): java.lang.NullPointerException
03-21 07:35:29.128: E/AndroidRuntime(1443): at com.example.certify_teacher_login.Certify_Absent_List$Absent_list_bg_task.onPostExecute(Certify_Absent_List.java:121)
03-21 07:35:29.128: E/AndroidRuntime(1443): at com.example.certify_teacher_login.Certify_Absent_List$Absent_list_bg_task.onPostExecute(Certify_Absent_List.java:1)
03-21 07:35:29.128: E/AndroidRuntime(1443): at android.os.AsyncTask.finish(AsyncTask.java:632)
03-21 07:35:29.128: E/AndroidRuntime(1443): at android.os.AsyncTask.access$600(AsyncTask.java:177)
03-21 07:35:29.128: E/AndroidRuntime(1443): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
03-21 07:35:29.128: E/AndroidRuntime(1443): at android.os.Handler.dispatchMessage(Handler.java:102)
03-21 07:35:29.128: E/AndroidRuntime(1443): at android.os.Looper.loop(Looper.java:137)
03-21 07:35:29.128: E/AndroidRuntime(1443): at android.app.ActivityThread.main(ActivityThread.java:4998)
03-21 07:35:29.128: E/AndroidRuntime(1443): at java.lang.reflect.Method.invokeNative(Native Method)
03-21 07:35:29.128: E/AndroidRuntime(1443): at java.lang.reflect.Method.invoke(Method.java:515)
03-21 07:35:29.128: E/AndroidRuntime(1443): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
03-21 07:35:29.128: E/AndroidRuntime(1443): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
03-21 07:35:29.128: E/AndroidRuntime(1443): at dalvik.system.NativeStart.main(Native Method)
答案 0 :(得分：2)
修改 在你的onCreate中你需要取消注释：
//setContentView(R.layout.);
并添加要加载的布局（listView1所在的位置）。
setContentView(R.layout.your_layout_name);
之后，使用以下命令加载listView：
listview = (ListView) findViewById(R.id.your_list_view_id);
其他：永远不要private static ListView listview;这会导致应用程序内存泄漏，不要对视图保持静态引用，如果执行中有多个活动，可能会导致崩溃。
答案 1 :(得分：0)
尝试使用以下代码。
JSONArray jarray;
jarray= new JSONArray(result);//result is your response from webservice
String []name= new String[jarray.length()];
for(int f=0;f<jarray.length();f++){
JSONObject jobj = jarray.getJSONObject(f);
name[f]= jobj.getString("Childname");
}
for(int a=0;a<jarray.length();a++){
items.add(new EntryItem(name[a]);//items is your listview and Enrty Item is your POJO class.
}
adapter = new EntryAdapter(contact.this,items);//Entry adapter is your adapter class.
lv.setAdapter(adapter);
答案 2 :(得分：0)
//setContentView(R.layout.);
为什么该行被评论？您不会扩展ListActivity或使用片段。除非是输入错误，否则它无法正常工作！