如何解决ArrayIndexOutOfBoundsException

Question

I am trying to access all the data from database "listOfFolder" table "folder" and want to store the data in a string array folders[] but i am getting how to resolve ArrayIndexOutOfBoundsException.

try{

  mydb = openOrCreateDatabase("listOfFolder", MODE_WORLD_WRITEABLE, null);  

    } catch (Exception e) {
        // TODO: handle exception
        e.printStackTrace();
      }

int count = 0;
String folders[] = null;
Cursor folderCursor = mydb.query("folder", null, null, null, null, null, null); 
while(folderCursor.moveToNext()) {

  folders[count] = folderCursor.getString(folderCursor.getColumnIndex("name"));
                    count++;
}

ListView list = (ListView)findViewById(R.id.lv);
ArrayAdapter<String> adapter = new ArrayAdapter<String>(DropboxActivity.this, android.R.layout.simple_list_item_1,folders);
list.setAdapter(adapter);
setContentView(R.layout.listoffolder);

Answer 1

Here's your problem:

String folders[] = null;

What did you expect to happen?

This code is a bad idea, because you have no idea how large a set the query will bring back. You have to call new to allocate a large enough array.

I'd prefer a collection like a List if it's available to you. Check this one out, too.

Answer 2

Change

String folders[] = null;
Cursor folderCursor = mydb.query("folder", null, null, null, null, null, null); 
while(folderCursor.moveToNext()){
    folders[count] = folderCursor.getString(folderCursor.getColumnIndex("name"));
    count++;
}

to

Cursor folderCursor = mydb.query("folder", null, null, null, null, null, null);
if (folderCursor.moveToFirst()) {
    String folders[] = new String[folderCursor.getCount()];
    do {
        folders[count] = folderCursor.getString(folderCursor.getColumnIndex("name"));
        count++;
    } while(folderCursor.moveToNext());
}

Answer 3

Like this:

ArrayList<datatypehere> namehere=new ArrayList<datatypehere>();

Then you can add elements to the list by:

String example1 = "this is a string";
namehere.add(example1);

Theres quite abit on lists in the JavaDocs and Java Tutorials if you search for them.