VB.NET：处理多个下拉列表

Question

I have this confusion in my mind whenever I have to deal with many dropdownlist (ddl). My question is actually is there any best practice or in-built functions or some work around to deal with such situation. I have given below a scenario as a test case. Lets say I have 4 ddl which are dependent upon the selection of the previous ones.

ddlContinent   ddlCountry   ddlCity   ddlCurrency
NorthAmerica   USA          Mumbai    Indian Rupee
Europe         Canada       Colombo   Sri Lanka Rupee
Asia           England      Paris     USD
[All]          India        London    Candian Dollar
               France       Chicago   GBP
               Sri Lanka    Toronto
               [All]        New Delhi
                            [All]  

Case1: If someone selects ddlContinent [All] and ddlCountry India; the ddlCity should be Mumbai and New Delhi Case2: If ddlContinent is Asia and ddlCountry is [All] then ddlCity should be Mumbai, New Delhi and Colombo

And so on..

The nightmare is that we need to code all the possible if-then conditions for the whole set of possibilities.

Above all, when the actual final output has to be displayed in a Table Object based on the above ddl selections, there again we have to code all the possible if-then conditions.

Is there a short-cut.

Note: The above is a ASP.NET Web Application

Thanks in advance.

Answer 1

well i resolved it using one custom class maybe exists better approach but here we go

Rules

 each ddl have one level
 top level affect to lower ddl

Tools

 one stored procedure 

Sketch

public class DdlLevel
{
  private DropDownList _ddl;
  private IRepository _repository;      
  private int _level;
  private string _displayField;
  private string _valueField;

  public DdlLevel(DropDownList ddl,int level, IRepository repository, string displayField, string valueField ){
    _ddl = ddl;
    _level = level;
    _repository = repository;
    _displayField = displayField; 
    _valueField = valueField;
  }

  public void Refresh(UserOptions userOptions){
    if userOptions.DdlLevelRaiseRefresh > _level){
    DataTable data = _repository.GetTablaFilter(userOptions)
    _dll.DataSource = data;
    _dll.DataTextField = _displayField;
    _dll.DataValueField = _valueField;
    _dll.DataBind();
    if (_dll.Item.Count > 0) _dll.SelectedIndex = 0; 
   }
  }
}   

in the page do some how

private IList<DdlLevel> _ddlRefresh;

page_load(){
  _dllRefresh = DllLevelInit();
}

IList<DdlLevel> DllLevelInit(){
  IList<DdlLevel> list = new List<DdlLevel>();
  list.add(new DdlLevel(firstdll,9,new yourRepository(...),"fieldtodisplay","fieldtostore");
  list.add(new DdlLevel(seconddll,8,new yourRepository(...),"fieldtodisplay","fieldtostore");
  ...
  return list;
}

now on each ddl put the same function(in this case Filter) for SelectedIndexChanged event

protected void Filter(Object sender, EventArgs e){
    UserOptions options = GetCurrentValuesOfDll(sender);
    for each DdlLevel ddl in _ddlRefresh
       dld.Refresh(options);
}

private UserOptions GetCurrentValuesOfDll(Object sender){
 UserOptions o = new UserOptions;   
    o.DdlLevelRaiseRefresh = GetLevelOfCurrentDdl(sender)
    o.DdlCompany = null;
    If Not (ddlCompany.SelectedValue = "All" Or ddlCompany.SelectedValue = "") Then
        o.DdlCompany = CType(ddlCompany.SelectedValue, Integer)
    End If
   ...
  return o;
}

private int GetLevelOfCurrentDdl(Object sender){
 int level = 0;
 switch(sender.ID){
   case "ddlCompany";
        return 9;
  ...
 }
 return level;
}

the sp is some how

create stored procedure DllFilterOnMyPage(useroption1, useroption2...)
as
 set nocount on

 if (dllLevel > 8) select 'All' as DisplayField, -0 as ValueToStore union select * from yourtable 
 if (dllLevel > 7) select 'All' as DisplayField, -0 as ValueToStore union select * from yourtable
 ...