SectionIndexer示例

This small tutorial will show you how to create a ListView, enable fast scrolling, and create a alphabetical section list that displays the letter as you quickly scroll the list.

这个简单的教程会教你创建一个ListView，实现快速滑动，并且创建一个按字母排序的分类的列表。当你快速滑动的时候，就会显示一个字母，表示当前滚动的位置。

First lets create a layout file with a ListView in it list this

首先创建一个存在ListView的布局文件

代码如下：

 <?xml version="1.0" encoding="utf-8"?>

 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
                 android:layout_width="fill_parent"
                 android:layout_height="fill_parent"
                 android:background="@drawable/background">

     <ListView
             android:id="@+id/thelist"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:scrollbars="vertical"
             android:fadingEdge="vertical"
             android:cacheColorHint="#00000000"
             android:fastScrollEnabled="true"
             android:padding="2dp">
     </ListView>
 </LinearLayout>

Notice I am putting a background image on the layout and setting the ListView to be transparent with the cacheColorHint. I also set fastScrollEnabled to true. Now I have a store object to store the attributes about a store.

请注意我为整个布局设置了一个背景图片，用cacheColorHint属性吧Listview设置为透明。我也把fastScrollEnabled 属性设置为true了。 接下来我用一个store对象存储了一些关于store的属性。

public class Store {

    public int id;
    public String name;
    public String direction;
    public int floor;
    public String address;
    public String category;
    public String phone;
}

Finally we need to create the Activity. We will assign a custom ArrayAdapter to the list and the custom ArrayAdapter will implement SectionIndexer
最后，我们需要创建一个Activity。我们需要指派一个实现了SectionIndexer接口的自定义的ArrayAdapter给这个ListView。

/**
* The Store List Activity
*/
public class StoreListActivity extends Activity {
    private DBAdapter db;

    private LinkedList<Store> storeList = new LinkedList<Store>();
    private StoreListAdaptor storeListAdaptor;

    private ListView list;

    /**
     * Called when the activity is first created.
     */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.storelist);

        list = (ListView) findViewById(R.id.thelist);

        // populate the store list
        storeList = db.getAllStoresOrderByName(storeList);

        // create an adaptor with the store list
        storeListAdaptor = new StoreListAdaptor(this,storeList);

        // assign the listview an adaptor
        list.setAdapter(storeListAdaptor);

    }

    /**
     * The List row creator
     */
    class StoreListAdaptor extends ArrayAdapter<Store> implements SectionIndexer{

        HashMap<String, Integer> alphaIndexer;
        String[] sections;

        public StoreListAdaptor(Context context, LinkedList<Store> items) {
            super(context, R.layout.storerow, items);

            alphaIndexer = new HashMap<String, Integer>();
            int size = items.size();

            for (int x = 0; x < size; x++) {
                Store s = items.get(x);

                // get the first letter of the store
                String ch =  s.name.substring(0, 1);
                // convert to uppercase otherwise lowercase a -z will be sorted after upper A-Z
                ch = ch.toUpperCase();

                // HashMap will prevent duplicates
                alphaIndexer.put(ch, x);
            }

            Set<String> sectionLetters = alphaIndexer.keySet();

            // create a list from the set to sort
            ArrayList<String> sectionList = new ArrayList<String>(sectionLetters); 

            Collections.sort(sectionList);

            sections = new String[sectionList.size()];

            sectionList.toArray(sections);
        }

       public View getView(int position, View convertView, ViewGroup parent) {
            // expand your row xml if you are using custom xml per row
       } 

       public int getPositionForSection(int section) {
           return alphaIndexer.get(sections[section]);
       }

       public int getSectionForPosition(int position) {
           return 1;
       }

       public Object[] getSections() {
            return sections;
       }
    }
}