I’ve an app that populates an ArrayList from a webservice. The webservice is called from an AsyncTask. The ArrayList is populated when i test it in the onPostExecute. The ArrayList is defined as an instance variable. Why when AsyncTask finishes is the arrayList populated but when i test the instance variable itself after, it’s null. It seems like Async is not setting the values properly.
Once Async has finished i am passing the ArrayList to an arrayAdapter, but my listView is empty.
Tests: in onPostExecute
Log.e(TAG, "array from WS = " + array.size()); // returns 4
tests: in onCreate
Log.e(TAG, "checking to see if array is null " + array.size()); // returns 0
package com.carefreegroup;
public class GetRotaDetails extends NfcBaseActivity implements OnItemClickListener
{
ArrayList<ArrayList<String>> array;
MySimpleArrayAdapter arrayAdapter;
Intent intent;
private static final String TAG = GetRotaDetails.class.getSimpleName();
ListView listView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
array = new ArrayList<ArrayList<String>>();
nfcscannerapplication = (NfcScannerApplication) getApplication();
intent = this.getIntent();
setContentView(R.layout.getrotadetailslayout);
listView = (ListView) findViewById(R.id.getrotadetailslistview);
//set titlebar to carer's name
Cursor cursorCarerName = nfcscannerapplication.loginValidate.queryAllFromCarer();
cursorCarerName.moveToLast();
String carerTitleName = cursorCarerName.getString(cursorCarerName
.getColumnIndex(LoginValidate.C_CARER_NAME));
setTitle(carerTitleName + " is currently logged in");
callID = intent.getStringExtra("callIDExtra");
Log.e(TAG, "callID = " + callID);
String[] params = { callID };
AsyncGetRotaDetails agrd = new AsyncGetRotaDetails();
agrd.execute(params);
Log.e(TAG, "checking to see if array is null " + array.size());
if (arrayAdapter == null){
MySimpleArrayAdapter arrayAdapter = new MySimpleArrayAdapter(this, array);
listView.setAdapter(arrayAdapter);
}
listView.setAdapter(arrayAdapter);
listView.setOnItemClickListener(this);
}// end of onCreate
@Override
protected void onResume() {
super.onResume();
}
private class AsyncGetRotaDetails extends AsyncTask<String, Void, String> {
ProgressDialog progressDialog;
String rotaDetails = null;
@Override
protected void onPreExecute() {
progressDialog = ProgressDialog
.show(GetRotaDetails.this, "Connecting to Server",
" retrieving rota details...", true);
};
@Override
protected String doInBackground(String... params) {
try {
Log.e(TAG, "inside doInBackground");
rotaDetails = nfcscannerapplication.loginWebservice.getRotaDetail(params[0]);
} catch (Exception e) {
e.printStackTrace();
}
return rotaDetails;
}
@Override
protected void onPostExecute(String xmlResult) {
super.onPostExecute(xmlResult);
if (progressDialog != null)
progressDialog.dismiss();
if (rotaDetails != null) {
RetrieveExtraDetails red = new RetrieveExtraDetails();
array = red.getExtraDetails(xmlResult);
Log.e(TAG, "array from WS = " + array.size());
} else {
AlertDialog alertDialog = new AlertDialog.Builder(
GetRotaDetails.this).create();
alertDialog.setTitle("Signal/Server Test");
alertDialog.setMessage("No Phone Signal or Server Problem");
alertDialog.setButton("OK",
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,
int which) {
onStart();
}
});
alertDialog.show();
}
}// end of postExecute
}//end of Async
private class MySimpleArrayAdapter extends ArrayAdapter<String> {
private final Context context;
private final ArrayList<?> list;
public MySimpleArrayAdapter(Context context, ArrayList<?> list) {
super(context, R.layout.getrotadetailsrow);
Log.e(TAG, "inside adapter constructor");
this.context = context;
this.list = list;
}// end of constructor
@Override
public View getView(int position, View convertView, ViewGroup parent) {
LayoutInflater inflater = (LayoutInflater) context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View rowView = inflater.inflate(R.layout.getrotadetailsrow, parent,
false);
TextView recTypeID = (TextView) rowView
.findViewById(R.id.rectypeid);
TextView recType = (TextView) rowView
.findViewById(R.id.rectype);
TextView name = (TextView) rowView
.findViewById(R.id.name);
TextView relationship = (TextView) rowView
.findViewById(R.id.relationship);
TextView address = (TextView) rowView
.findViewById(R.id.address);
TextView postCode = (TextView) rowView
.findViewById(R.id.postcode);
TextView telNo = (TextView) rowView
.findViewById(R.id.telno);
TextView keySafe = (TextView) rowView
.findViewById(R.id.keysafe);
TextView notes = (TextView) rowView
.findViewById(R.id.notes);
TextView meds = (TextView) rowView
.findViewById(R.id.meds);
String record = list.get(position).toString();
Log.e(TAG, "record = " + record);
recTypeID.setText(record);
return super.getView(position, convertView, parent);
}
}
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
// TODO Auto-generated method stub
}
}
Make your ListView a field in the class and
Use
in onPostExecute(String result) method
but what i recommend is:
Use a loading spinner until the data is fetched and adapter is set, otherwise the behavior is the Activity shows up as empty and after 3-5 secs suddenly the whole list appears, which is a bad UX.
Usually we use Async Tasks without any loading spinner when the data being fetched is a small part of the UI, not a ListView which is a major component of the UI.
and don’t check the length of the Array in onCreate(). It will always be 0. Because the code flow will be :
1. Create Array
2. Check its length in onCreate //0 as nothing is added yet
3. Add data to the Array in background
4. Check its length in onPostExecute(String result) //actual length