[安卓]Cursor用法

Cursor用于数据库的查询读取，

主要方法：moveToFist moveToNext moveToPrevious getCount getColumnIndex getColumnIndexOrThrow

getColumnName getColumnNames moveToPosition getPosition

Cursor每次只读表中一行数据，读完后用moveToNext方法读下一行。

数据库转换成对象的方法如下：

private People[] ConvertToPeople(Cursor cursor){
        int resultCounts = cursor.getCount();//总共的数据量
        if(resultCounts == 0 || !cursor.moveToFirst()){//指针移动到第一条数据不成功
            return null;
        }
        People[] peoples = new People[resultCounts];//
        for(int i=0;i<resultCounts;i++){
            peoples[i] = new People();
            peoples[i].ID = cursor.getInt(0);//获取每行数据的ID
            peoples[i].Name = cursor.getString(cursor.getColumnIndex(KEY_NAME));//获取对应数据行的KEY的String
            peoples[i].Age = cursor.getInt(cursor.getColumnIndex(KEY_AGE));//获取对应数据行的KEY的int
            peoples[i].Height = cursor.getInt(cursor.getColumnIndex(KEY_HEIGHT));//获取对应数据行的KEY的int
            cursor.moveToNext();
        }
        return peoples;//返回对象
    }

private SQLiteDatabase db;
//数据库插入数据
public long insert(People people){
        ContentValues newValue = new ContentValues();
        newValue.put(KEY_NAME,people.Name);
        newValue.put(KEY_AGE,people.Age);
        newValue.put(KEY_HEIGHT,people.Height);
        return db.insert(DB_TABLE,null,newValue);
    }
    //数据库删除所有数据
    public long deleteAllData(){
        return db.delete(DB_TABLE, null, null);
    }
//数据库删除指定id的数据    
public long deleteOneData(long id){
        return db.delete(DB_TABLE, KEY_ID + "="+ id,null);
    }
//查询表中所有数据    
public People[] queryAllData(){
        Cursor results = db.query(DB_TABLE,new String[] { KEY_ID,KEY_NAME,KEY_AGE,KEY_HEIGHT},null,null,null,null,null);
        return ConvertToPeople(results);
    }
//查询表中指定id的数据    
public People[] queryOneDta(long id){
        Cursor results = db.query(DB_TABLE,new String[] {KEY_ID, KEY_NAME, KEY_AGE, KEY_HEIGHT},KEY_ID+"="+id,null,null,null,null);
        return ConvertToPeople(results);
    }
//更新表中数据    
public long updateOneData(long id, People people){
        ContentValues updateValues = new ContentValues();
        updateValues.put(KEY_NAME,people.Name);
        updateValues.put(KEY_AGE,people.Age);
        updateValues.put(KEY_HEIGHT,people.Height);
        return db.update(DB_TABLE,updateValues, KEY_ID + "=" + id,null);
    }