Android学习系列(15)--App列表之游标ListView(索引ListView)
游标ListView,提供索引标签,使用户能够快速定位列表项。
也可以叫索引ListView,有的人称也为Tweaked ListView,可能更形象些吧。
一看图啥都懂了:
1.游标(Fast scroll thumb)
就是右边的那个拖动的方块,这个非常的简单:
<ListView android:id="@+id/tweaked_list" android:layout_width="fill_parent" android:layout_height="wrap_content" android:fastScrollEnabled="true"/>
也可以用在java后台书写:
tweakedListView.setFastScrollEnabled(true);
在数据量有一定大的时候,滑动列表,就会出现右边的所谓的"游标"了。
简单,这也是我为什么私下里喜欢自己写控件,但是工作中却喜欢用通用控件。
我们看下源代码,其实就是启用FastScroller对象:
//启用FastScroller对象 public void setFastScrollEnabled(boolean enabled) { mFastScrollEnabled = enabled; if (enabled) { if (mFastScroller == null) { mFastScroller = new FastScroller(getContext(), this); } } else { if (mFastScroller != null) { mFastScroller.stop(); mFastScroller = null; } } }
2.字母索引
在Android学习系列(10)--App列表之拖拽ListView(上)中我们使用了一种WindowManager在ListView中添加一些自定义影像,这种方法我觉得一定是可行的。
但是,android系统给我们提供了一个更简单的方法:使用AlphabetIndexer。
AlphabetIndexer,实现了SectionIndexer接口,是adapter的一个辅助类,辅助实现在快滑时,显示索引字母。
使用字母索引的话,必须保证数据列表是按字母顺序排序,以便AlphabetIndexerh采用二分查找法快速定位。
/** * Cursor表示数据游标 * sortedColumnIndex数据集合中的第几列 * alphabet字母列表,用的最多的是"ABCDEFGHIJKLMNOPQRSTUVWXYZ" **/ public AlphabetIndexer(Cursor cursor, int sortedColumnIndex, CharSequence alphabet) {}
用到3个方法:
//这三个方法,实现了索引数据和列表数据的对应和定位 public int getPositionForSection(int section) {} public int getSectionForPosition(int position) {} public Object[] getSections() {}
3.游标Cursor的实现
Cursor接口的实现,有两种选择:
(1).直接使用数据库查询返回的cursor
(2).自定义实现Cursor接口的新类
第一种方式很简单,查询一下数据库返回Cursor即可。
这里我们以第二种方式实践,伪装一个Cursor,主要是实现3个方法:
(1).getCount()
(2). moveToPosition()
(3). getString()
/** * 伪装一个Cursor供AlphabetIndexer作数据索引源 */ private class IndexCursor implements Cursor{ private ListAdapter adapter; private int position; private Map<String, String> map; public IndexCursor(ListAdapter adapter){ this.adapter = adapter; } @Override public int getCount() {return this.adapter.getCount();} /** * 取得索引字母,这个方法非常重要,根据实际情况具体处理 */ @SuppressWarnings("unchecked") @Override public String getString(int columnIndex) { map = (HashMap<String, String>)adapter.getItem(position); return map.get(key).substring(0,1); } @Override public boolean moveToPosition(int position) { if(position<-1||position>getCount()){ return false; } this.position = position; //如果不满意位置有点向上偏的话,下面这几行代码是修复定位索引值为顶部项值的问题 //if(position+2>getCount()){ // this.position = position; //}else{ // this.position = position + 2; //} return true; } @Override public void close() {} @Override public void copyStringToBuffer(int arg0, CharArrayBuffer arg1) {} @Override public void deactivate() {} @Override public byte[] getBlob(int arg0) {return null;} @Override public int getColumnCount() {return 0;} @Override public int getColumnIndex(String columnName) {return 0;} @Override public int getColumnIndexOrThrow(String columnName) throws IllegalArgumentException {return 0;} @Override public String getColumnName(int columnIndex) {return null;} @Override public String[] getColumnNames() {return null;} @Override public double getDouble(int columnIndex) {return 0;} @Override public Bundle getExtras() {return null;} @Override public float getFloat(int columnIndex) {return 0;} @Override public int getInt(int columnIndex) {return 0;} @Override public long getLong(int columnIndex) {return 0;} @Override public int getPosition() {return position;} @Override public short getShort(int columnIndex) {return 0;} @Override public boolean getWantsAllOnMoveCalls() {return false;} @Override public boolean isAfterLast() {return false;} @Override public boolean isBeforeFirst() {return false;} @Override public boolean isClosed() {return false;} @Override public boolean isFirst() {return false;} @Override public boolean isLast() {return false;} @Override public boolean isNull(int columnIndex) {return false;} @Override public boolean move(int offset) {return false;} @Override public boolean moveToFirst() {return false;} @Override public boolean moveToLast() {return false;} @Override public boolean moveToNext() {return false;} @Override public boolean moveToPrevious() {return false;} @Override public void registerContentObserver(ContentObserver observer) {} @Override public void registerDataSetObserver(DataSetObserver observer) {} @Override public boolean requery() {return false;} @Override public Bundle respond(Bundle extras) {return null;} @Override public void setNotificationUri(ContentResolver cr, Uri uri) {} @Override public void unregisterContentObserver(ContentObserver observer) {} @Override public void unregisterDataSetObserver(DataSetObserver observer) {} }
这个类的实例就可作为AlphaIndexer的构造函数第一个参数数据游标。
4.自定义Adapter的实现
使用前面介绍的东西,我们来实现最终的IndexAdapter:
class IndexAdapter extends SimpleAdapter implements SectionIndexer{ private AlphabetIndexer alphabetIndexer; public IndexAdapter(Context context,List<? extends Map<String, ?>> data, int resource,String[] from, int[] to) { super(context, data, resource, from, to); //设置数据游标 //设置索引字母列表 alphabetIndexer = new AlphabetIndexer(new IndexCursor(this), 0, "ABCDEFGHIJKLMNOPQRSTUVWXYZ"); } @Override public Object[] getSections() { return alphabetIndexer.getSections(); } @Override public int getPositionForSection(int section) { return alphabetIndexer.getPositionForSection(section); } @Override public int getSectionForPosition(int position) { return alphabetIndexer.getSectionForPosition(position); } }
5.跑起来
提供样本数据如下:
public List<Map<String, String>> getData(){ List<Map<String, String>> itemList = new ArrayList<Map<String, String>>(); String alphas = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; Map<String, String> map = null; for(char c:alphas.toCharArray()){ for(int i=0; i<10; i++){ map = new HashMap<String, String>(); map.put("itemText", ""+c+i); itemList.add(map); } } return itemList; }
子项的布局文件:
<?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="50dip" android:gravity="center_vertical" > <TextView android:id="@+id/tweaked_item_text" android:layout_width="fill_parent" android:layout_height="wrap_content" /> </LinearLayout>
使用并运行:
protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.tweake_list); tweakedListView = (ListView)findViewById(R.id.tweaked_list); //获取数据 List<Map<String, String>> itemList = getData(); ListAdapter adapter = new IndexAdapter(this, itemList, R.layout.tweake_list_item, new String[]{"itemText"}, new int[]{R.id.tweaked_item_text}); tweakedListView.setAdapter(adapter); }
效果如下:
6.小结
这种索引效果,在大数据量列表显示中非常的实用,是android开发必备常识。
本文只是一个简单的sample,实际工作中肯定会需要进一步扩展定义:
(1).对于复杂类型的处理,可根据Map<String,?>扩展自定义实体类,再通过adapter转换使用即可。
(2).对于索引字母列表,可动态设置,举个例子,你的列表只有ABCD四个字母,如果索引字母列表还是设置“ABCDEFGHIJKLMNOPQRSTUVWXYZ”就不合适了,会有个索引偏位的问题。
(3).对于复杂界面的显示,可重写adapter的getView方法自定义视图。
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