伪装游标

伪装游标挺实用的，不用在数据库中查询也可以使用游标

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) {}
        
   }

如ListView的索引用到的 

AlphabetIndexer alphabetIndexer = new AlphabetIndexer(new IndexCursor(this), 0, "ABCDEFGHIJKLMNOPQRSTUVWXYZ");

就可以使用伪装游标从自己数据源获取，不一定先查询数据库了。