Android 片段中的NullPointerException';s OnCreateView()
我在Fragement的OnCreateView()方法中得到一个NullPointerException。我试过好几种方法,但错误不断出现。我认为错误来自listview 这是我的代码:Android 片段中的NullPointerException';s OnCreateView(),android,json,listview,fragment,Android,Json,Listview,Fragment,我在Fragement的OnCreateView()方法中得到一个NullPointerException。我试过好几种方法,但错误不断出现。我认为错误来自listview 这是我的代码: package com.imptmd.charliemacdonald.desleutelaar; import android.app.ProgressDialog; import android.content.Intent; import android.os.AsyncTask; imp
package com.imptmd.charliemacdonald.desleutelaar;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.app.ListFragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.TextView;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.HashMap;
public class SlotenFragment extends ListFragment {
private ProgressDialog nDialog;
// URL to get contacts JSON
private static String url = "http://charlenemacdonald.com/sloten.json";
// JSON Node names
private static final String TAG_SLOTEN = "slotenlijst";
private static final String TAG_SLOT = "Slot";
// contacts JSONArray
JSONArray sloten= null;
// Hashmap for ListView
ArrayList<HashMap<String, String>> slotenLijst;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
final View rootView = inflater.inflate(R.layout.fragment_sloten, container, false);
slotenLijst = new ArrayList<HashMap<String, String>>();
ListView lv = (ListView) getView().findViewById(android.R.id.list);
// Listview on item click listener
lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
// getting values from selected ListItem
String Slot = ((TextView) rootView.findViewById(R.id.textviewslotnaam))
.getText().toString();
// Starting single contact activity
Intent in = new Intent(getActivity().getApplicationContext(),
SlotInfoScherm1.class);
in.putExtra(TAG_SLOT, Slot);
startActivity(in);
}
});
return rootView;
// Calling async task to get json
}
/**
* Async task class to get json by making HTTP call
* */
private class GetSloten extends AsyncTask<Void, Void, Void> {
@Override
protected void onPreExecute() {
super.onPreExecute();
// Showing progress dialog
nDialog = new ProgressDialog(getActivity());
nDialog.setMessage("Even geduld a.u.b., studenten worden geladen...");
nDialog.setCancelable(false);
nDialog.show();
}
@Override
protected Void doInBackground(Void... arg0) {
// Creating service handler class instance
ServiceHandler sh = new ServiceHandler();
// Making a request to url and getting response
String jsonStr = sh.makeServiceCall(url, ServiceHandler.GET);
Log.d("Response: ", "> " + jsonStr);
if (jsonStr != null) {
try {
JSONObject jsonObj = new JSONObject(jsonStr);
// Getting JSON Array node
sloten = jsonObj.getJSONArray(TAG_SLOTEN);
// looping through All Contacts
for (int i = 0; i < sloten.length(); i++) {
JSONObject c = sloten.getJSONObject(i);
String Slot = c.getString(TAG_SLOT);
// tmp hashmap for single contact
HashMap<String, String> sloten = new HashMap<String, String>();
// adding each child node to HashMap key => value
sloten.put(TAG_SLOT, Slot);
// adding contact to contact list
slotenLijst.add(sloten);
}
} catch (JSONException e) {
e.printStackTrace();
}
} else {
Log.e("ServiceHandler", "Couldn't get any data from the url");
}
return null;
}
@Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
// Dismiss the progress dialog
if (nDialog.isShowing())
nDialog.dismiss();
/**
* Updating parsed JSON data into ListView
* */
ListAdapter adapter = new SimpleAdapter(getActivity(), slotenLijst,
R.layout.sloten_info, new String[] { TAG_SLOT}, new int[] { R.id.textviewslotnaam});
setListAdapter(adapter);
}
}
}
package com.imptmd.charliemacdonald.desleutelaar;
导入android.app.ProgressDialog;
导入android.content.Intent;
导入android.os.AsyncTask;
导入android.os.Bundle;
导入android.support.v4.app.ListFragment;
导入android.util.Log;
导入android.view.LayoutInflater;
导入android.view.view;
导入android.view.ViewGroup;
导入android.widget.AdapterView;
导入android.widget.ListAdapter;
导入android.widget.ListView;
导入android.widget.simpledapter;
导入android.widget.TextView;
导入org.json.JSONArray;
导入org.json.JSONException;
导入org.json.JSONObject;
导入java.util.ArrayList;
导入java.util.HashMap;
公共类SlotenFragment扩展了ListFragment{
私人住宅;
//获取联系人JSON的URL
专用静态字符串url=”http://charlenemacdonald.com/sloten.json";
//JSON节点名称
私有静态最终字符串标记\u SLOTEN=“slotenlijst”;
私有静态最终字符串标记\u SLOT=“SLOT”;
//联系JSONArray
JSONArray sloten=null;
//ListView的Hashmap
ArrayList slotenLijst;
@凌驾
创建视图上的公共视图(布局、充气机、视图组容器、,
Bundle savedInstanceState){
最终视图根视图=充气机。充气(R.layout.fragment\u sloten,容器,假);
slotenLijst=newarraylist();
ListView lv=(ListView)getView().findViewById(android.R.id.list);
//单击项目上的Listview侦听器
lv.setOnItemClickListener(新的AdapterView.OnItemClickListener(){
@凌驾
public void onItemClick(AdapterView父级、视图、,
内部位置,长id){
//从选定的ListItem获取值
字符串槽=((TextView)rootView.findViewById(R.id.textviewslotnaam))
.getText().toString();
//启动单一联系人活动
意向输入=新意向(getActivity().getApplicationContext(),
SlotInfoScherm1.class);
in.putExtra(标签槽、槽);
星触觉(in);
}
});
返回rootView;
//调用异步任务以获取json
}
/**
*异步任务类通过HTTP调用获取json
* */
私有类GetSloten扩展异步任务{
@凌驾
受保护的void onPreExecute(){
super.onPreExecute();
//显示进度对话框
nDialog=newprogressdialog(getActivity());
nDialog.setMessage(“甚至geduld a.u.b.,studenten worden geladen…”);
nDialog.setCancelable(假);
nDialog.show();
}
@凌驾
受保护的Void doInBackground(Void…arg0){
//创建服务处理程序类实例
ServiceHandler sh=新的ServiceHandler();
//向url发出请求并获得响应
字符串jsonStr=sh.makeServiceCall(url,ServiceHandler.GET);
Log.d(“响应:”、“>”+jsonStr);
if(jsonStr!=null){
试一试{
JSONObject jsonObj=新的JSONObject(jsonStr);
//获取JSON数组节点
sloten=jsonObj.getJSONArray(TAG_sloten);
//通过所有触点循环
for(int i=0;ivalue
插槽。放置(标记插槽,插槽);
//将联系人添加到联系人列表
slotenLijst.add(sloten);
}
}捕获(JSONException e){
e、 printStackTrace();
}
}否则{
Log.e(“ServiceHandler”,“无法从url获取任何数据”);
}
返回null;
}
@凌驾
受保护的void onPostExecute(void结果){
super.onPostExecute(结果);
//关闭进度对话框
if(nDialog.isShowing())
nDialog.discouse();
/**
*将解析的JSON数据更新到ListView中
* */
ListAdapter=new SimpleAdapter(getActivity(),slotenLijst,
R.layout.sloten_info,新字符串[]{TAG_SLOT},新int[]{R.id.textviewslotnaam});
setListAdapter(适配器);
}
}
}
提前谢谢 在onCreateView()方法中,替换
ListView lv = (ListView) getView().findViewById(android.R.id.list);
与
在onCreateView()
返回之前,不能调用getView()
方法,因为getView()
实际上返回了由onCreateView()
在rootView
上调用findViewById()
创建的视图,而不是在活动上
刚才膨胀的视图层次结构还不是活动视图层次结构的一部分。多次询问getView()在onCreateView中返回null
ListView lv = (ListView) rootView.findViewById(android.R.id.list);