Achieve level two drop-down box linkage

1. Realize the linkage of level two drop-down box.

Function: Implementation Click the Grade drop-down box to load the corresponding account drop-down box.

First step: Load the data in the Grade drop-down box first.

01. Write a method in the Gradedal layer (data access layer) to query all grade information.

/// <summary>        ///get grade information from the database/// </summary>        /// <returns>Collection of list: Grade number, Grade name</returns>         PublicList<grade>Selectgradeinfo () {List<Grade> list =NewList<grade>(); stringsql ="SELECT * from Grade"; DataTable DT=sqlhelper.executedatatable (SQL); foreach(DataRow Iteminchdt. Rows) {//an item represents a row objectGrade Grade =NewGrade (); Grade. Gradeid= Convert.ToInt32 (item["Gradeid"]); Grade. Gradename=item["Gradename"].               ToString (); List.           ADD (grade); }           returnlist; }

02. The method of invoking the data access layer at the GRADEBLL layer (the Business logic layer) is returned to the UI layer for invocation.

  Public classGRADEBLL {gradedal gd=NewGradedal (); /// <summary>        ///get grade information from the database/// </summary>        /// <returns>Collection of list: Grade number, Grade name</returns>        PublicList<grade>Selectgradeinfo () {returnGD.       Selectgradeinfo (); }        }

03. At the UI layer (presentation layer) Call the GRADEBLL layer method, receive it with the list<grade> type, bind to the drop-down box, and implement the binding of the Grade drop-down box.

//load the Grade drop-down box method, make a call in the Load event         Public voidLoadingcbograde () {//method of calling the BLL layer, receiving it with the list collectionlist<grade> list =GB.            Selectgradeinfo (); //The binding displays the value. Cbograde. DisplayMember ="Gradename"; //binds hidden values. Cbograde. ValueMember ="Gradeid"; //Binding Data SourcesCbograde. DataSource =list; }

Step two: In the Grade drop-down box, the SelectedIndexChanged (event triggered when the property value changes) loads the corresponding account information for that grade by calling the BLL layer method.

01. Write a method on the Subjectdal layer to query the grade's hidden value (that is, the grade number) according to the selected grade, and return a collection of subject objects.

  /// <summary>       ///search for subjects under this grade based on the selected grade number/// </summary>       /// <returns>collection of Account objects</returns>        PublicList<subject> Selectsubjectinfos (intID) {//Query account information based on grade number           stringsql ="Select Subjectid,subjectname from subject where [email protected]"; SqlParameter SP=NewSqlParameter ("@gradeid", id); DataTable DT=sqlhelper.executedatatable (SQL,SP); List<Subject> list =NewList<subject>(); foreach(DataRow Iteminchdt. Rows) {Subject Subject=NewSubject (); Subject. Subjectid= Convert.ToInt32 (item["Subjectid"]); Subject. Subjectname= item["Subjectname"].               ToString (); List.           ADD (subject); }           returnlist; }

02. The method of invoking the data access layer at the SUBJECTBLL layer is returned to the UI layer to invoke.

   /// <summary>       /// Search for subjects       under this grade based on the selected grade number /// </summary>       /// <returns> collection of Account objects </returns>         Public List<subject> Selectsubjectinfos (int  ID)        {            return  SD. Selectsubjectinfos (ID);        }

03. Call the SUBJECTBLL layer method in the SelectedIndexChanged (event triggered when the property value changes) in the Grade drop-down box

 //Instantiate SUBJECTBLLSUBJECTBLL SB =NewSUBJECTBLL (); //Grade drop-down box property change value triggered event        Private voidCbograde_selectedindexchanged (Objectsender, EventArgs e) {           //Get Grade number            intId=Convert.ToInt32 (Cbograde.            SelectedValue); //a method called the BLL layer is received with a collection of subject typesList<subject> list=sb.            Selectsubjectinfos (ID); //add an item all in the Account down box. List. Insert (0,NewSubject {subjectid=-1, subjectname="All" }); //empty drop-down box dataCbosubject. DataSource =NULL; //Binding Display ValuesCbosubject. DisplayMember ="Subjectname"; //binding hidden ValuesCbosubject. ValueMember ="Subjectid"; //Binding Data SourcesCbosubject. DataSource =list; }

Achieve level two drop-down box linkage