Android Wizard

Fast Scroll List View

Posted on 13. Jun, 2010 by Admin in Beginner

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >

<ListView
android:id="@+id/myListView"
android:layout_width="fill_parent"
 android:layout_height="fill_parent">
</ListView>

</LinearLayout>

package ch.egsolutions.tutorial;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Random;
import java.util.Set;

import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.util.Log;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.SectionIndexer;

public class AlphabetIndexer extends Activity {
     ListView myListView;
     ArrayList<String> elements;

     @Override
     public void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.main);

          // elements
          String s = "QWERTZUIOPASDFGHJKLYXCVBNM";
          Random r = new Random();
          elements = new ArrayList<String>();
          for (int i = 0; i < 300; i++) {

               elements.add(s.substring(r.nextInt(s.length())));

          }
          Collections.sort(elements); // Must be sorted!

          // listview
          myListView = (ListView) findViewById(R.id.myListView);
          myListView.setFastScrollEnabled(true);
          MyIndexerAdapter<String> adapter = new MyIndexerAdapter<String>(
                    getApplicationContext(), android.R.layout.simple_list_item_1,
                    elements);
          myListView.setAdapter(adapter);

     }

     class MyIndexerAdapter<T> extends ArrayAdapter<T> implements SectionIndexer {

          ArrayList<String> myElements;
          HashMap<String, Integer> alphaIndexer;

          String[] sections;

          public MyIndexerAdapter(Context context, int textViewResourceId,
                    List<T> objects) {
               super(context, textViewResourceId, objects);
               myElements = (ArrayList<String>) objects;
               // here is the tricky stuff
               alphaIndexer = new HashMap<String, Integer>();
               // in this hashmap we will store here the positions for
               // the sections

               int size = elements.size();
               for (int i = size - 1; i >= 0; i--) {
                    String element = elements.get(i);
                    alphaIndexer.put(element.substring(0, 1), i);
               //We store the first letter of the word, and its index.
               //The Hashmap will replace the value for identical keys are putted in
               }

               // now we have an hashmap containing for each first-letter
               // sections(key), the index(value) in where this sections begins

               // we have now to build the sections(letters to be displayed)
               // array .it must contains the keys, and must (I do so...) be
               // ordered alphabetically

               Set<String> keys = alphaIndexer.keySet(); // set of letters ...sets
               // cannot be sorted...

               Iterator<String> it = keys.iterator();
               ArrayList<String> keyList = new ArrayList<String>(); // list can be
               // sorted

               while (it.hasNext()) {
                    String key = it.next();
                    keyList.add(key);
               }

               Collections.sort(keyList);

               sections = new String[keyList.size()]; // simple conversion to an
               // array of object
               keyList.toArray(sections);

               // ooOO00K !

          }

          @Override
          public int getPositionForSection(int section) {
               // Log.v("getPositionForSection", ""+section);
               String letter = sections[section];

               return alphaIndexer.get(letter);
          }

          @Override
          public int getSectionForPosition(int position) {

               // you will notice it will be never called (right?)
               Log.v("getSectionForPosition", "called");
               return 0;
          }

          @Override
          public Object[] getSections() {

               return sections; // to string will be called each object, to display
               // the letter
          }

     }
}

Tags: fast scroll, ListView