首先，我开发了一个 Activity，其中解析 json 输出并将其显示在列表中。效果很好。然后，我将代码从 Activity 转换为 Fragment，如下所示。现在，当执行 AsyncTask 时，我得到一个 NullPointerException。
没有 AsyncTask 它也能工作。这就是为什么我在网上发表评论，
task.execute();。
数据来自服务器，因此使用AsyncTask是必要的。
有人可以帮我解决这个问题吗？
public class FragmentLoadtransferAddon extends SherlockFragment {
ProgressBar webservicePG;
ListAdapter adapter ;
ListView lv;
String empid=null;
ArrayList<HashMap<String, String>> dataList ;
HashMap<String, String> map;
private static final String TAG_ITEMNAME = "ItemCode";
private static final String TAG_QTY = "Quantity";
public FragmentLoadtransferAddon() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.loadtransferaddon, container, false);
dataList = new ArrayList<HashMap<String, String>>();
lv=(ListView) rootView.findViewById(R.id.loadtransfer_form_addon_ListView);
webservicePG = (ProgressBar) rootView.findViewById(R.id.daystart_form_progressBar1);
adapter = new SimpleAdapter(getActivity(), dataList,
R.layout.rawcurrentstock,
new String[] { TAG_ITEMNAME, TAG_QTY}, new int[] {
R.id.rawcurrentsock_form_productname,R.id.rawcurrentsock_form_productqty});
//
return rootView;
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onActivityCreated(savedInstanceState);
AsyncCallWS task = new AsyncCallWS();
// // Call execute
// task.execute();
String json = AddonWebService.invokeDaystartWS(empid,
"GetLoadItems");
if (json != null) {
try {
if (json.contains("<!--"))
json = json.substring(0, json.indexOf("<!--"));
Log.d("Response according to Gettabledata after :: ", " "
+ json);
jsonObj.getJSONArray("Table");
JSONArray tarray = new JSONArray(json);
Log.d("tarraytable: ",
" " + tarray);
for (int i = 0; i < tarray.length(); i++) {
JSONObject jsonChildNode = tarray.getJSONObject(i);
String name = jsonChildNode.getString(TAG_ITEMNAME);
String qty = jsonChildNode.getString(TAG_QTY);
// creating new HashMap
map = new HashMap<String, String>();
// adding each child node to HashMap key => value
map.put(TAG_ITEMNAME, name);
map.put(TAG_QTY, qty);
dataList.add(map);
}
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
} else {
Log.e("JSON Data", "Didn't receive any data from server!");
}
lv.setAdapter(adapter);
}
private class AsyncCallWS extends AsyncTask<String, Void, Void> {
@Override
protected void onPreExecute() {
webservicePG.setVisibility(View.VISIBLE);
super.onPreExecute();
}
@Override
protected Void doInBackground(String... params) {
String json = AddonWebService.invokeDaystartWS(empid,
"GetLoadItems");
if (json != null) {
try {
if (json.contains("<!--"))
json = json.substring(0, json.indexOf("<!--"));
Log.d("Response according to Gettabledata after :: ", " "
+ json);
JSONArray tarray = new JSONArray(json);
Log.d("tarraytable: ",
" " + tarray);
for (int i = 0; i < tarray.length(); i++) {
JSONObject jsonChildNode = tarray.getJSONObject(i);
String name = jsonChildNode.getString(TAG_ITEMNAME);
String qty = jsonChildNode.getString(TAG_QTY);
// creating new HashMap
map = new HashMap<String, String>();
// adding each child node to HashMap key => value
map.put(TAG_ITEMNAME, name);
map.put(TAG_QTY, qty);
dataList.add(map);
}
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
} else {
Log.e("JSON Data", "Didn't receive any data from server!");
}
return null;
}
@Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
webservicePG.setVisibility(View.GONE);
lv.setAdapter(adapter);
}
}
日志猫
03-17 12:17:17.087: E/AndroidRuntime(342): java.lang.NullPointerException
03-17 12:17:17.087: E/AndroidRuntime(342): at com.winwrench.pos.fragments.FragmentLoadtransferAddon$AsyncCallWS.onPreExecute(FragmentLoadtransferAddon.java:110)
03-17 12:17:17.087: E/AndroidRuntime(342): at android.os.AsyncTask.execute(AsyncTask.java:391)
03-17 12:17:17.087: E/AndroidRuntime(342): at com.winwrench.pos.fragments.FragmentLoadtransferAddon.onActivityCreated(FragmentLoadtransferAddon.java:59)
03-17 12:17:17.087: E/AndroidRuntime(342): at android.support.v4.app.Fragment.performActivityCreated(Fragment.java:1508)
03-17 12:17:17.087: E/AndroidRuntime(342): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:947)
03-17 12:17:17.087: E/AndroidRuntime(342): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)
03-17 12:17:17.087: E/AndroidRuntime(342): at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
03-17 12:17:17.087: E/AndroidRuntime(342): at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1467)
03-17 12:17:17.087: E/AndroidRuntime(342): at android.support.v4.app.Fragment.performStart(Fragment.java:1521)
03-17 12:17:17.087: E/AndroidRuntime(342): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:957)
03-17 12:17:17.087: E/AndroidRuntime(342): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)
03-17 12:17:17.087: E/AndroidRuntime(342): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1086)
03-17 12:17:17.087: E/AndroidRuntime(342): at android.support.v4.app.FragmentManagerImpl.dispatchStart(FragmentManager.java:1889)
03-17 12:17:17.087: E/AndroidRuntime(342): at android.support.v4.app.Fragment.performStart(Fragment.java:1530)
03-17 12:17:17.087: E/AndroidRuntime(342): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:957)
03-17 12:17:17.087: E/AndroidRuntime(342): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)
03-17 12:17:17.087: E/AndroidRuntime(342): at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
03-17 12:17:17.087: E/AndroidRuntime(342): at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1467)
03-17 12:17:17.087: E/AndroidRuntime(342): at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:440)
03-17 12:17:17.087: E/AndroidRuntime(342): at android.os.Handler.handleCallback(Handler.java:587)
03-17 12:17:17.087: E/AndroidRuntime(342): at android.os.Handler.dispatchMessage(Handler.java:92)
03-17 12:17:17.087: E/AndroidRuntime(342): at android.os.Looper.loop(Looper.java:123)
03-17 12:17:17.087: E/AndroidRuntime(342): at android.app.ActivityThread.main(ActivityThread.java:3683)
03-17 12:17:17.087: E/AndroidRuntime(342): at java.lang.reflect.Method.invokeNative(Native Method)
03-17 12:17:17.087: E/AndroidRuntime(342): at java.lang.reflect.Method.invoke(Method.java:507)
03-17 12:17:17.087: E/AndroidRuntime(342): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
03-17 12:17:17.087: E/AndroidRuntime(342): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
03-17 12:17:17.087: E/AndroidRuntime(342): at dalvik.system.NativeStart.main(Native Method)
最佳答案
NPE 发生在代码的以下行:
webservicePG.setVisibility(View.VISIBLE);
您在以下行启动 webservicePG:
webservicePG = (ProgressBar) rootView.findViewById(R.id.daystart_form_progressBar1);
因此，请确保 loadtransferaddon.xml 内有 id = daystart_form_progressBar1(区分大小写)
关于android - 在 Android Fragment 中实现 AsyncTask，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/22450603/