I know it's simple question, but in
ArrayList<ArrayList<String>> collection;
ArrayList<String> listOfSomething;
collection= new ArrayList<ArrayList<String>>();
listOfSomething = new ArrayList<String>();
listOfSomething.Add("first");
listOfSomething.Add("second");
collection.Add(listOfSomething);
listOfSomething.Clear();
listOfSomething.Add("first");
collection.Add(listOfSomething);
I want to take String from ArrayList of ArrayList, and I don't know how to do that. For example I go
ArrayList<String> myList = collection.get(0);
String s = myList.get(0);
and it works! but:
private List<S> valuesS;
private List<Z> valuesZ;
ArrayList<ArrayList<String>> listOfS;
ArrayList<String> listOfZ;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Zdatasource = new ZDataSource(this);
Zdatasource.open();
valuesZ = Zdatasource.getAllZ();
Sdatasource = new SDataSource(this);
Sdatasource.open();
valuesS = Sdatasource.getAllS();
List<Map<String, String>> groupData
= new ArrayList<Map<String, String>>();
List<List<Map<String, String>>> childData
= new ArrayList<List<Map<String, String>>>();
listOfS = new ArrayList<ArrayList<String>>();
listOfZ = new ArrayList<String>();
for (S i : valuesS) { // S is class
for (Z j : valuesZ) { // Z is class
if(j.getNumerS().equals(i.getNumerS())) {
listOfZ.add(j.getNumerZ());
}
else
{
//listOfZ.add("nothing");
}
}
listOfS.add(listOfZ);
if(!listOf.isEmpty()) listOfZ.clear();
}
@Override
public boolean onChildClick(ExpandableListView parent, View v, int groupPosition,
int childPosition, long id) {
try
{
ArrayList<String> myList = listOfS.get(groupPosition);
String s = myList.get(childPosition);
PrintToast("group "+Integer.toString(groupPosition)+", child "+Integer.toString(childPosition) + " , "+ s);
}
catch(Exception e)
{
Log.e("FS", e.toString());
}
return true;
}
return me java.lang.IndexOutOfBoundsException: Invalid index 1, size is 0 when I click on item which really should exist. I didn't show code which generate ListView, but I can tell you that my listOfS contains 3 items: first is Null listOfZ, second listOfZ got 2 elements, third listOfZ got 1 element.
listOfSomething.Clear();
listOfSomething.Add("first");
collection.Add(listOfSomething);
You are clearing the list here and adding one element ("first"), the 1st reference of listOfSomething
is updated as well sonce both reference the same object, so when you access the second element myList.get(1)
(which does not exist anymore) you get the null.
Notice both collection.Add(listOfSomething);
save two references to the same arraylist object.
You need to create two different instances for two elements:
ArrayList<ArrayList<String>> collection = new ArrayList<ArrayList<String>>();
ArrayList<String> listOfSomething1 = new ArrayList<String>();
listOfSomething1.Add("first");
listOfSomething1.Add("second");
ArrayList<String> listOfSomething2 = new ArrayList<String>();
listOfSomething2.Add("first");
collection.Add(listOfSomething1);
collection.Add(listOfSomething2);
Because the second element is null after you clear the list.
Use:
String s = myList.get(0);
And remember, index 0 is the first element.
The right way to iterate on a list inside list is:
//iterate on the general list
for(int i = 0 ; i < collection.size() ; i++) {
ArrayList<String> currentList = collection.get(i);
//now iterate on the current list
for (int j = 0; j < currentList.size(); j++) {
String s = currentList.get(1);
}
}
A cleaner way of iterating the lists is:
// initialise the collection
collection = new ArrayList<ArrayList<String>>();
// iterate
for (ArrayList<String> innerList : collection) {
for (String string : innerList) {
// do stuff with string
}
}
Source: Stackoverflow.com