如何将会话变量数组的值无效为null

问题描述

美好的一天.

在这里，我正在开发具有五个DropDownList控件(级联)的应用程序，该功能具有在没有子树可用时自动隐藏的功能，以及将"SelectedItem" ID存储到五个会话变量的功能，到目前为止，很好，但是当我触发上层(例如，第二个DDL及其在Session ["s3"]中在DDL3中有子树)的DDL选择时，如果新结果没有生成子树，它将隐藏第三个DDL(i' (很高兴)，但其Session值未更改为null，请尝试满足我的要求，请检查我的代码

Hi, good day.

Here i''m developing a application with five DropDownList Controls (cascading), with functionality to hide automatically when no sub-tree is availabe, along with that i''m storing "SelectedItem" IDs to five session variables, upto now everything is fine, but when i trigger selectionevent of upper(say 2nd DDL which is having a subtree in DDL3 along with Session["s3"]) DDL selection, if the new result doen''t generate a subtree it hides 3rd DDL (i''m happy) but its Session value is not changing to null, here give a try to readch my requirement, please check my code

// Global variables with private acess level
string _L1, _L2, _L3, _L4, _L5;

string[] Values;

_L1 = _L2 = _L3 = _L4 = _L5 = null; // in PageLOading (!Page.IsPostback)

public void HideRemainingDDLs(DropDownList _ddlname)
{
// _ddlname is the name of DropDownList, which doesn''t have a sub-tree, in our case DDL2


 //
_L1 = Session["L1ID"] == null ? null : Session["L1ID"].ToString();
_L2 = Session["L2ID"] == null ? null : Session["L2ID"].ToString();
_L3 = Session["L3ID"] == null ? null : Session["L3ID"].ToString();
_L4 = Session["L4ID"] == null ? null : Session["L4ID"].ToString();
_L5 = Session["L5ID"] == null ? null : Session["L5ID"].ToString();

UpdatePanel up = (UpdatePanel)TagEditor;

Values = new string[5] { _L1, _L2, _L3, _L4, _L5 }; // Storing Session Variable as a string array

if (up.HasControls())
{
foreach (Control subCtrl in up.Controls[0].Controls)
{
if (subCtrl is DropDownList) // Check only if the Controls is a DropDownList
{
DropDownList ddl = subCtrl as DropDownList;
if (ddl.Visible == true) // Check only visible controls
{
if (ddl != null && ddl.TabIndex > _ddlname.TabIndex) // DDL TabIndex starts from 0
{
int i = ddl.TabIndex;
Values[i] = null;
ddl.Visible = false; // Hide the current DDL
ddl.Items.Clear(); // remove all items in the DDL
}
}
}
}
}
}


Example DDL SelectedIndexChanged Event

protected void DDLSubL1_SelectedIndexChanged(object sender, EventArgs e)
{
if (populate("PopulateL2Subjects", DDLSubL2, DDLSubL1, out _subject1)) // method to retive data from DB, returns bool value.
{
DDLSubL2.Visible = true;
}
else
{
HideRemainingDDLs(DDLSubL1); // Method which is implemented above
DDLSubL2.Items.Add("Select chapter");
}
// set the value irrespective of new list.
Session["L1ID"]= _subject1;
} 

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