请仔细阅读以下代码并帮助我。来自url的数据正在被解析，但我无法填入列表视图。
public class HomeFragment extends Fragment {
View rootView = null;
private ListView myListView;
private String[] strListView;
private String[] categ;
private TextView catName;
private CustomAdapter myAdapter;
private DownloadJson downloadJson;
private int i;
private AsyncTask task;
private Thread thread;
public HomeFragment()
{
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setHasOptionsMenu(true);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
rootView = inflater.inflate(R.layout.fragment_home, container, false);
myListView = (ListView) rootView.findViewById(R.id.listview);
new DownloadJson().execute();
// Inflate the layout for this fragment
return rootView;
}
这是callCustomAdapter功能：
public void callCustomAdaper( Context context)
{
myAdapter = new CustomAdapter(context);
myListView.setAdapter(myAdapter);
myListView.setOnItemClickListener(new android.widget.AdapterView.OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
Log.v("Module Item Trigger", "Module item was triggerted");
/* Fragment customMapFragmentMapFragment = new MessagesFragment();
FragmentManager fragmentManager = getActivity().getSupportFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.container, customMapFragmentMapFragment)
.addToBackStack(null)
.commit();*/
}
});
}
这个类是json解析器：
class DownloadJson extends AsyncTask {
Activity context;
ListView myListView;
private ProgressDialog dialog = new ProgressDialog(getActivity());
public DownloadJson(Activity context, ListView myListView) {
this.myListView = myListView;
this.context = context;
}
public DownloadJson() {
}
@Override
protected void onPreExecute() {
this.dialog.setMessage("Please wait");
this.dialog.show();
}
@Override
protected void onCancelled() {
super.onCancelled();
}
@Override
protected Object doInBackground(Object[] params) {
String result = null;
InputStream isr = null;
String imageId = null;
String ip = "http://ganarajsshetti.tk/mobileapp/selectjson.php/";
try {
HttpClient httpClient = new DefaultHttpClient();
HttpGet httpGet = new HttpGet(ip);
HttpResponse httpResponse = httpClient.execute(httpGet);
HttpEntity httpEntity = httpResponse.getEntity();
isr = httpEntity.getContent();
} catch (Exception e) {
Log.e("log_tag", "Error in http Connection" + e.toString());
}
// converting response to string
try {
BufferedReader br = new BufferedReader(new InputStreamReader(isr));
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = br.readLine()) != null) {
sb.append(line + "\n");
}
isr.close();
result = sb.toString();
} catch (Exception e) {
Log.e("log_tag", "Error in Converting Data" + e.toString());
}
// parse JSON data
try {
JSONArray jsonArray = new JSONArray(result);
strListView = new String[jsonArray.length()];
for (int i = 0; i < jsonArray.length(); i++) {
JSONArray json_data = jsonArray.getJSONArray(i);
for (int j =0; j< json_data.length();j++) {
strListView[i] = json_data.getString(j);
System.out.println("--------------" + json_data.getString(0));
}
Log.e("ACK_tag", "DATA" + strListView[i]);
}
} catch (Exception e) {
Log.e("log_tag", "Error in parsing Data" + e.toString());
}
return null;
}
@Override
protected void onPostExecute(Object o) {
// ArrayAdapter objAdapter = new ArrayAdapter<String>(context,R.layout.list_item,R.id.Category,strListView);
if (dialog.isShowing()) {
dialog.dismiss();
}
callCustomAdaper(context);
}
}
这是扩展基本适配器的customAdapter：
public class CustomAdapter extends BaseAdapter {
private Context context;
public CustomAdapter(Context context) {
this.context = context;
}
@Override
public int getCount() {
return strListView.length;
}
@Override
public Object getItem(int i) {
return strListView[i];
}
@Override
public long getItemId(int i) {
return i;
}
@Override
public View getView(int i, View convertview, ViewGroup viewGroup) {
View row= null;
if(convertview == null) {
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
row = inflater.inflate(R.layout.list_item, viewGroup, false);
}
else{
row= convertview;
}
catName=(TextView) row.findViewById(R.id.Category);
catName.setText(categ[i]);
return row;
}
public String[] getValues()
{
return strListView;
}
}
这些是我的Xml文件：
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context="info.androidhive.materialdesign.activity.HomeFragment">
<ListView
android:id="@+id/listview"
android:layout_width="wrap_content"
android:layout_height="wrap_content">
</ListView>
</RelativeLayout>
这是其他xml：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent"
android:padding="10dp"
android:paddingLeft="10dp"
android:paddingRight="10dp">
<TextView
android:id="@+id/Category"
android:layout_width="50dp"
android:layout_height="50dp"
android:gravity="center_horizontal"
android:textStyle="bold"/>
</LinearLayout>
这就是我得到的错误：
java.lang.NullPointerException：尝试调用虚方法＆＃39; java.lang.Object android.content.Context.getSystemService（java.lang.String）＆＃39;在null对象引用上 在info.androidhive.materialdesign.activity.HomeFragment $ CustomAdapter.getView（HomeFragment.java:248）
答案 0 :(得分：0)
您正在使用错误的构造函数（空的）创建DownloadJson
答案 1 :(得分：0)
您的上下文传递给适配器时出现问题。在您的片段中，您正在调用new DownloadJson().execute();因此您不会向AsyncTask发送上下文，因此无法将其发送到适配器。您应该使用另一个构造函数new DownloadJson(getActivity(), myListView).execute();
还有一件事你不应该将Activity保存为上下文。当您不需要时，您正在泄漏活动将其保留在内存中。在AsyncTask中使用private Context context;，并将此上下文设为getActivity().getApplicationContext();