我试图在android中的服务器上显示可扩展列表视图中的数据。我正在尝试在AsyncTask中实现hashmap。请参阅以下代码。
private class HttpAsyncTaskReports extends AsyncTask<String, Void, String> {
private ProgressDialog dialog;
public HttpAsyncTaskReports(ExpandableActivity activity) {
dialog = new ProgressDialog(activity);
}
@Override
protected String doInBackground(String... urls) {
return GET(urls[0]);
}
@Override
protected void onPreExecute() {
// Removes all markers, overlays, and polylines from the map.
dialog.setMessage("Loading reports, please wait.");
dialog.show();
}
@Override
protected void onPostExecute(String result) {
if (dialog.isShowing()) {
dialog.dismiss();
}
listDataHeader = new ArrayList<String>();
listDataChild = new HashMap<String, List<String>>();
// Header, Child data
List<String> top250 = new ArrayList<String>();
top250.add("The Shawshank Redemption");
top250.add("The Godfather");
try {
JSONArray jArray = new JSONArray(result);
JSONObject jsonobject = jArray.getJSONObject(0);
JSONArray jsonAssets = jsonobject.getJSONArray("last_data");
Log.d("LASTLATLONG", result);
for (i = 0; i < jsonAssets.length(); i++) {
JSONObject nlmJsonObject = jsonAssets.getJSONObject(i);
JSONObject lastData_JsonObject = nlmJsonObject.getJSONObject("last_data");
JSONObject lastData_timeJsonObject = lastData_JsonObject.getJSONObject("time");
// JSONObject lastData_dateJsonObject = lastData_timeJsonObject.getJSONObject("$date");
// JSONObject lastData_speedJsonObject = lastData_JsonObject.getJSONObject("speed");
// Adding child data
listDataHeader.add(lastData_timeJsonObject.getString("$date"));
listDataChild.put(listDataHeader.get(i), top250);
}
} catch (JSONException e) {
e.printStackTrace();
Toast.makeText(getApplicationContext(), "Server Error :( Please wait!", Toast.LENGTH_LONG).show();
}
}
}
这是ExpandableListAdapter类
public class ExpandableListAdapter extends BaseExpandableListAdapter {
private Context _context;
private List<String> _listDataHeader; // header titles
// child data in format of header title, child title
private HashMap<String, List<String>> _listDataChild;
public ExpandableListAdapter(Context context, List<String> listDataHeader,
HashMap<String, List<String>> listChildData) {
this._context = context;
this._listDataHeader = listDataHeader;
this._listDataChild = listChildData;
}
@Override
public Object getChild(int groupPosition, int childPosititon) {
return this._listDataChild.get(this._listDataHeader.get(groupPosition))
.get(childPosititon);
}
@Override
public long getChildId(int groupPosition, int childPosition) {
return childPosition;
}
@Override
public View getChildView(int groupPosition, final int childPosition,
boolean isLastChild, View convertView, ViewGroup parent) {
final String childText = (String) getChild(groupPosition, childPosition);
if (convertView == null) {
LayoutInflater infalInflater = (LayoutInflater) this._context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = infalInflater.inflate(R.layout.list_item, null);
}
TextView txtListChild = (TextView) convertView
.findViewById(R.id.lblListItem);
txtListChild.setText(childText);
return convertView;
}
@Override
public int getChildrenCount(int groupPosition) {
return this._listDataChild.get(this._listDataHeader.get(groupPosition))
.size();
}
@Override
public Object getGroup(int groupPosition) {
return this._listDataHeader.get(groupPosition);
}
@Override
public int getGroupCount() {
return this._listDataHeader.size();
}
@Override
public long getGroupId(int groupPosition) {
return groupPosition;
}
@Override
public View getGroupView(int groupPosition, boolean isExpanded,
View convertView, ViewGroup parent) {
String headerTitle = (String) getGroup(groupPosition);
if (convertView == null) {
LayoutInflater infalInflater = (LayoutInflater) this._context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = infalInflater.inflate(R.layout.list_group, null);
}
TextView lblListHeader = (TextView) convertView
.findViewById(R.id.lblListHeader);
lblListHeader.setTypeface(null, Typeface.BOLD);
lblListHeader.setText(headerTitle);
return convertView;
}
@Override
public boolean hasStableIds() {
return false;
}
@Override
public boolean isChildSelectable(int groupPosition, int childPosition) {
return true;
}
}
这是错误......
java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3124)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3233)
at android.app.ActivityThread.access$1000(ActivityThread.java:197)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1656)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:6856)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1404)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1199)
Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
at gps.finder.com.findermaterial.ExpandableListAdapter.getGroupCount(ExpandableListAdapter.java:75)
at android.widget.ExpandableListConnector.getCount(ExpandableListConnector.java:397)
at android.widget.ListView.setAdapter(ListView.java:502)
at android.widget.ExpandableListView.setAdapter(ExpandableListView.java:604)
at gps.finder.com.findermaterial.ExpandableActivity.onCreate(ExpandableActivity.java:102)
at android.app.Activity.performCreate(Activity.java:6550)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1120)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3077)
有人能告诉我该如何解决这个问题？
如果我使用类似下面的函数列出数据，它会成功运行。
private void prepareListData() {
listDataHeader = new ArrayList<String>();
listDataChild = new HashMap<String, List<String>>();
// Adding child data
listDataHeader.add("Top 50");
listDataHeader.add("Now Showing");
listDataHeader.add("Coming Soon..");
// Adding child data
List<String> top250 = new ArrayList<String>();
top250.add("The Shawshank Redemption");
top250.add("The Godfather");
top250.add("The Godfather: Part II");
top250.add("Pulp Fiction");
top250.add("The Good, the Bad and the Ugly");
top250.add("The Dark Knight");
top250.add("12 Angry Men");
List<String> nowShowing = new ArrayList<String>();
nowShowing.add("The Conjuring");
nowShowing.add("Despicable Me 2");
nowShowing.add("Turbo");
nowShowing.add("Grown Ups 2");
nowShowing.add("Red 2");
nowShowing.add("The Wolverine");
List<String> comingSoon = new ArrayList<String>();
comingSoon.add("2 Guns");
comingSoon.add("The Smurfs 2");
comingSoon.add("The Spectacular Now");
comingSoon.add("The Canyons");
comingSoon.add("Europa Report");
listDataChild.put(listDataHeader.get(0), top250); // Header, Child data
listDataChild.put(listDataHeader.get(1), nowShowing);
listDataChild.put(listDataHeader.get(2), comingSoon);
}
但我需要使用从服务器检索的数据来实现hashmap。
感谢您的建议。提前谢谢。