记录转化为有层次结构的树状列表的通用算法

转载：http://www.cnblogs.com/ejiyuan/archive/2007/11/27/973765.html

 

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问题说明:

在获取数据库记录数据的时候, 通常返回的ArrayList集合, 没有了层次关系. 如果每次根据PID重新到数据库获取记录, 可以做到, 但有以下几个缺点:

1. 访问数据库记录次数随着记录的增多而增多

2. 由于需要多次访问数据库, 因此访问速度受影响

3. 需要数据库访问层的支持, 并对记录进行转化, 耦合性太强

4. 通用性不好, 每次需要一个新的类型列表, 就需要

解决方法:

我根据原有的树状结构算法代码, 编写一个通用的算法, 利用反射原理, 递归的对数据进行筛选.

这样只需要访问数据库一次, 然后就在内存中遍历, 而且适合于所有具有(PID, ID, Name)属性的实体类集合的排序.

 

如我需要生成设备类型实体类集合的树状结构时候, 代码如下:

 

ArrayList equipTypelist = equipmentType.GetAll(); equipTypelist = CollectionHelper.GetTreeItems(equipTypelist); this.ddlEquipmentTypes.DataSource = equipTypelist; this.ddlEquipmentTypes.DataTextField = "Name"; this.ddlEquipmentTypes.DataValueField = "ID"; this.ddlEquipmentTypes.DataBind(); this.ddlEquipmentType.Items.Insert(0, new ListItem("(全部)", "0"));

 

public class CollectionHelper { private static ArrayList Fill(int pID, int level, ArrayList list) { ArrayList returnList = new ArrayList(); foreach(object obj in list) { int typePID = (int)ReflectionUtil.GetProperty(obj, "PID"); int typeID = (int)ReflectionUtil.GetProperty(obj, "ID"); string typeName = ReflectionUtil.GetProperty(obj, "Name") as string; if(pID == typePID) { string newName = new string('-', level * 4) + typeName; ReflectionUtil.SetProperty(obj, "Name", newName); returnList.Add(obj); returnList.AddRange(Fill(typeID, level+1, list)); } } return returnList; } /**//// <summary> /// 生成有层次结构的列表 /// </summary> /// <param name="list">具有Name,ID,PID成员的任何集合</param> /// <returns></returns> public static ArrayList GetTreeItems(ArrayList list) { return Fill(-1, 0, list); } }

 

public sealed class ReflectionUtil { private ReflectionUtil() { } public static BindingFlags bf = BindingFlags.DeclaredOnly | BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static; public static void SetProperty(object obj, string name, object value) { PropertyInfo fi = obj.GetType().GetProperty(name, bf); fi.SetValue(obj, value,null); } public static object GetProperty(object obj, string name) { PropertyInfo fi = obj.GetType().GetProperty(name, bf); return fi.GetValue(obj,null); }}

 

 

效果图如下