Exercise: WinForm Three-level linkage (Chinese administrative divisions)

usingSystem;usingSystem.Collections.Generic;usingSystem.Linq;usingSystem.Text;namespacethree-level linkage. model{classChina {Private stringCode;  Public stringCode {Get{returnCode;} Set{Code =value;} }        Private stringname;  Public stringName {Get{returnname;} Set{name =value;} }        Private stringParentcode;  Public stringParentcode {Get{returnParentcode;} Set{Parentcode =value;} }    }}

entity class

usingSystem;usingSystem.Collections.Generic;usingSystem.Linq;usingSystem.Text;usingSystem.Data.SqlClient;namespacethree-level linkage. dataconnection{classDataConnection {Private Static stringConnstr="server=; database=mydb; user=sa; Pwd=ray ;";  Public StaticSqlConnection Conn {Get{return NewSqlConnection (CONNSTR);} }    }}

Data Connection Class

usingSystem;usingSystem.Collections.Generic;usingSystem.Linq;usingSystem.Text;usingSystem.Data.SqlClient;namespacethree-level linkage. dataoperation{classChinadata {PrivateSqlConnection _conn; PrivateSqlCommand _cmd; PrivateSqlDataReader _dr;  PublicChinadata () {_conn=DataConnection.DataConnection.Conn; _cmd=_conn.        CreateCommand (); }        //return region information based on parent code         PublicList<model.china> Select (stringPcode) {_cmd.commandtext="Select *from chinastates where [email protected]"; _cmd.            Parameters.clear (); _cmd. Parameters.addwithvalue ("@pcode", Pcode); _conn.            Open (); _DR=_cmd.            ExecuteReader (); List<Model.China> list =NewList<model.china>(); if(_DR. HasRows) { while(_DR. Read ()) {Model.china data=NewModel.china (); Data. Code= _dr[0].                    ToString (); Data. Name= _dr[1].                    ToString (); Data. Parentcode= _dr[2].                    ToString (); List.                ADD (data); }} _conn.            Close (); returnlist; }    }}

Data Manipulation Classes

Visual Interface Operation:

Background code:

usingSystem;usingSystem.Collections.Generic;usingSystem.ComponentModel;usingSystem.Data;usingSystem.Drawing;usingSystem.Linq;usingSystem.Text;usingSystem.Windows.Forms;namespacethree-level linkage { Public Partial classForm1:form { PublicForm1 () {InitializeComponent (); } dataoperation.chinadata CDA=NewDataoperation.chinadata (); //ways to fill the province         Public voidFillsheng () {List<Model.China> list = cda. Select ("0001"); Cmbsheng.datasource=list; Cmbsheng.displaymember="Name"; Cmbsheng.valuemember="Code"; }        //methods of filling the city         Public voidFillshi () {List<Model.China> list =CDA.            Select (CmbSheng.SelectedValue.ToString ()); Cmbshi.datasource=list; Cmbshi.displaymember="Name"; Cmbshi.valuemember="Code"; }        //methods for populating the area         Public voidFillqu () {List<Model.China> list =CDA.            Select (CmbShi.SelectedValue.ToString ()); Cmbqu.datasource=list; Cmbqu.displaymember="Name"; Cmbqu.valuemember="Code"; }        //Page One load run three methods        Private voidForm1_Load (Objectsender, EventArgs e)            {Fillsheng ();            Fillshi ();        Fillqu (); }        //Fill City drop-down list        Private voidCmbsheng_selectionchangecommitted (Objectsender, EventArgs e)            {Fillshi ();        Fillqu (); }        //Drop -down list of populated areas        Private voidCmbshi_selectionchangecommitted (Objectsender, EventArgs e)        {Fillqu (); }    }}

Exercise: WinForm Three-level linkage (Chinese administrative divisions)